Plz Note :
This Page Discusses Various Types Of Cisco Networking Questions And Answers. We Request To The Students, Please Go Through All The Articles (Notes) That Are We Posted In This Web Site And Identify All The CISCO IOS Commands In The Lab Practice Before Going To Access This Page. Thank You!
◙ - ➤ Cisco Routing And Switching (PART – 1 With 501 Questions & Answers):
Some Topics That You Might Want To Pursue On Your Own That We Did Not Cover In This Article Are Listed Here. The Work Described In This Article Is Mainly Focused On The Field Of “IP ROUTING, IP ADDRESSES, RIP, EIGRP, OSPF, BGP, IS-IS”.
On A Very Small Computer Network, It Is Feasible To Use Simple Broadcast Or Sequential Mechanisms For Moving Data From Point To Point. An Ethernet Local Area Network (LAN) Is Essentially A Broadcast Network. In Larger, More Complex Networks, Data Must Be Directed Specifically To The Intended Destination. Routers Direct Network Data Messages, Or Packets, Based On Internal Addresses And Tables Of Routes, Or Known Destinations That Serve Certain Addresses. Directing Data Between Portions Of A Network Is The Primary Purpose Of A Router. Most Large Computer Networks Use The TCP/IP Protocol Suite.
A LOCAL AREA NETWORK Is Composed Of A Relatively Small Number Of Hosts Connected Over A Relatively Small Physical Area. “Relatively Small” Is The Important Phrase Here. To Give Some Meaning To The Term “Relatively,” Consider That A 10 Base T Ethernet (10 Megabit Per Second Using Twisted Pair Cabling) Has A Usual Maximum Of 1024 Stations Over A Maximum Cable Distance Of 2500 Meters. For Instance, A Typical Office LAN, Using 100 baset Ethernet, Might Have 100 Computers (And Printers) Attached To A Switch Or Set Of Hubs.
AN ETHERNET LOCAL AREA NETWORK (LAN) Is Essentially A (Logical) Bus Based Broadcast Network; Though The Physical Implementation May Use Hubs (With A Physical Star Topology). As One Would Expect, Broadcast LANs Must Deal With Collisions; Either By Preventing Them Or Detecting Them And Taking Appropriate Action. Token Based LANs Avoid Collisions By Only Allowing One Host At Time To Transmit (The Host That Currently Has The Token May Transmit).
Standards That Relate To LANs Are Primarily The IEEE 802.X Series. For Instance, 802.3 Is The Media Access Control (MAC) Standard For CSMA/CD (The Ethernet Standard); While 802.5 Is The MAC Standard For Token Ring. Just Above The MAC Level Is The Logical Link Control (802.2) Standard And Above That It The High Level Interface (802.1) Standard. Within A LAN, Addressing Is Done With A MAC Address. Between LANs Using TCP/IP, Addressing Is Done Using IP Addresses.
MEDIA: One Of The First Things Done When Setting Up A Network Of Routers, Switches, And Host Devices Is The Creation Of Connections Between The Devices. This Connection Is Done Via Media. The Media Can Be Either Bounded (Cables) Or Unbounded (Wireless).
When Data Is Transmitted Across Media, Operations Are Occurring At The Network Interface Layer. This Layer Includes Both The Physical Implementation (Cable Type, Wireless Frequency, Connectors, And So On) And The Communication Method Employed By The Media (Ethernet, 802.11, Frame Relay, PPP).
Media Is Usually Used To Connect Infrastructure Devices Such As Switches And Routers. Moreover, The Management Of Infrastructure Devices Is Typically Done Via Wire, And Not Wirelessly In Accordance With Security Best Practices.
NETWORK DATA MESSAGES: From A LAN And Convert Them Into Packets Suitable For Transmission Beyond The LAN On A Wide Area Network (WAN). The Goal Is Almost Always To Get These Packets To Another LAN And Ultimately To The Correct Host On That LAN. Part Of The “Conversion” Process Is To Add A Packet Header. Other Routers Will Generally Only Look At A Packet’s Header Information, Not At The Contents Or Data In The Packet.
PURPOSE OF A ROUTER: In Larger, More Complex Computer Networks, Data Must Be Directed More Carefully. In Almost All Cases, Large Networks Are Actually Composed Of A Collection Of LANs That Are Interconnected Or “Internetworked”. This Is Where Routers Come In. Routers Take
ROUTERS HAVE BEEN KNOWN BY SEVERAL NAMES. Back In Ancient Times When What Is Now The Internet Was Called The ARPANET, Routers Were Called IMPs, For Interface Message Processors. More Recently, Routers Were Called Gateways; Remnants Of This Nomenclature Can Still Be Found In Terms Such As Border Gateway Protocol (BGP) And Interior Gateway Routing Protocol (IGRP). In The Open System Interconnection (OSI) World, Routers Are Known As Intermediate Systems (IS).
Also Make Decisions About Where To Send These Packets, Based On: The Addresses Contained Within The Packet Headers And A Table Of Routes Maintained Within The Router.
Updating These Routing Tables And Forwarding Data Packets Between Portions Of A Network Are Two Of The Primary Tasks Of A Router.
Building Packets And Unwrapping Packets Are Additional Router Functions Performed By The First And Last Routers, Respectively, That A Message Passes Through.
IN ADDITION To Directing Packets, A Router May Be Responsible For Filtering Traffic, Allowing Some Packets To Pass Through And Rejecting Others. Filtering Can Be A Very Important Function Of Routers; It Allows Them To Help Protect Computers And Other Network Components. It Is Also Possible That At The Destination End A Router May Have To Break Large Packets Up To Accommodate The Size Limits Of The Destination LAN.
ROUTE TABLES: As Mentioned, One Of Tasks Of A Router Is To Maintain Route Tables Which Are Used To Decide Where A Packet Is To Go And Thus Which Interface It Should Be Sent Out. In The Past These Tables Were Built And Updated By Hand And This Is Referred To As Static Routing. In Dynamic Routing, The Router Learns About Where Various Addresses Are Relative To Itself And Builds Up Route Tables Based On This Information.
SPECIAL PURPOSE ROUTER: What Are Some Of The Motivations For Using A Dedicated, Purpose-Built Router Rather Than A General Purpose Machine With A “Standard” Operating System (OS)? A Special Purpose Router Can Have Much Higher Performance Than A General Purpose Computer With Routing Functionality Tacked Onto It. Also, One Can Potentially Add More Network Connections To A Machine Designed For That Purpose, Because It Can Be Designed To Support More Interface Card Slots. Thus, A Special Purpose Device Will Probably Be A Lower Cost Solution For A Given Level Of Functionality. But There Are Also A Number Of Security Benefits To A Special Purpose Router; In General, Consolidating Network Routing And Related Functions On A Dedicated Devices Restricts Access To And Limits The Exposure Of Those Critical Functions.
Like CISCO’S INTERNETWORK OPERATING SYSTEM (IOS) Can Be Smaller, Better Understood, And More Thoroughly Tested Than A General Purpose OS ( IOS Will Be Used In This Guide To Refer The Router’s Operating System And Associated Software, But Hardware Other Than Cisco Would Run Similar Software) .
AN INTERIOR ROUTER Forwards Traffic Between Two Or More Local Networks Within An Organization Or Enterprise. The Networks Connected By An Interior Router Often Share The Same Security Policy, And The Level Of Trust Between Them Is Usually High. If An Enterprise Has Many Interior Routers, They Will Usually Employ An Interior Gateway Protocol To Manage Routes. Interior Routers May Impose Some Restrictions On The Traffic They Forward Between Networks.
A BACKBONE OR EXTERIOR ROUTER Is One That Forwards Traffic Between Different Enterprises (Sometimes Called Different ‘Autonomous Systems’). The Traffic Between The Different Networks That Make Up The Internet Is Directed By Backbone Routers. The Level Of Trust Between The Networks Connected By A Backbone Router Is Usually Very Low. Typically, Backbone Routers Are Designed And Configured To Forward Traffic As Quickly As Possible, Without Imposing Any Restrictions On It. The Primary Security Goals For A Backbone Router Are To Ensure That The Management And Operation Of The Router Are Conducted Only By Authorized Parties, And To Protect The Integrity Of The Routing Information It Uses To Forward Traffic. Backbone Routers Typically Employ Exterior Gateway Protocols To Manage Routes.
A BORDER ROUTER Forwards Traffic Between An Enterprise And Exterior Networks. The Key Aspect Of A Border Router Is That It Forms Part Of The Boundary Between The Trusted Internal Networks Of An Enterprise, And Untrusted External Networks (E.G. The Internet). It Can Help To Secure The Perimeter Of An Enterprise Network By Enforcing Restrictions On The Traffic That It Controls. A Border Router May Employ Routing Protocols, Or It May Depend Entirely On Static Routes.
It Has A Central Processor Unit (CPU), Various Kinds Of Memory, And Connections To Other Devices. The CPU, Also Called The Central Processor Or Route Processor, Provides High-Level Services For Management, Logging, Routing, And Control. It Loads The Configuration Of The Router During Boot-Up, And Manages The Operation Of The Interfaces. When Traffic Is Being Forwarded From One Network To Another, It Usually Does Not Touch The CPU; Instead, The Packets Travel Across The Routing Fabric From The Incoming Interface To The Appropriate Destination Interface. Only Management And Control Traffic For The Router Travel To Or From The CPU. This Can Be Important, Because The Bandwidth Of The Channel To The CPU May Be Far Smaller Than The Bandwidth Of The Interfaces.
There Are Typically A Number Of Types Of Memory In A Router Possibly Including: RAM, NVRAM, Flash, And ROM (PROM, EEPROM). These Are Listed Roughly In Order Of Volatility. The Mix Of Types And The Amount Of Each Type Are Determined On The Basis Of: Volatility, Ease Of Reprogramming, Cost, Access Speed, And Other Factors. ROM Is Used To Store A Router’s Bootstrap Software. Non-Volatile RAM (NVRAM) Is Used To Store The Startup Configuration That The IOS Reads When The Router Boots. Flash Memory Stores The IOS (Or Other Router OS), And If There Is Enough Flash It May Store More Than One Version Of IOS.
Interfaces Provide The Physical Connections From A Router To Networks. Interface Types Include Ethernet, Fast Ethernet, Gigibit-Ethernet, Token Ring, FDDI, Low-Speed Serial, Fast Serial, HSSI, ISDN BRI, Etc. Each Interface Is Named And Numbered. Interface Cards Fit Into Slots In A Router, And An External Cable Of The Appropriate Type Is Connected To The Card. In Addition To A Number Of Interfaces, Almost All Routers Have A Console Port Providing An Asynchronous Serial Connection (RS-232). Also, Most Routers Have An Auxiliary Port, Which Is Frequently Used For Connecting A Modem For Router Management.
Router Will Run A Control Program Or Operating System (OS). Each Router Vendor Supplies Their Own Router OS. In The Case Of Cisco Routers, They Run Cisco’s Internetwork Operating System (IOS). It Is The IOS That Interprets The Access Control List (ACL) Settings And Other Commands To The Router.
The Startup Or Backup Configuration Is Stored In NVRAM. It Is Executed When The Router Boots. As Part Of The Boot Process A Copy Of This Configuration Is Loaded Into RAM. Changes Made To A Running Configuration Are Usually Made Only In RAM And Generally Take Effect Immediately. If Changes To A Configuration Are Written To The Startup Configuration, Then They Will Also Take Effect On Reboot. Changes Made Only To The Running Configuration Will Be Lost Upon Reboot.
An Operational Router Will Have A Large Number Of Processes Executing To Support The Services And Protocols That The Router Must Support. All Routers Support A Variety Of Commands That Display Information About What Processes Are Running And What Resources, Such As CPU Time And Memory, They Are Consuming. Unneeded Services And Facilities Should Be Disabled To Avoid Wasting CPU And Memory Resources, And To Avoid Giving Attackers Additional Potential Avenues For Attack.
Each Router Should Have A Unique Name To Identify It, And Each Interface Should Have Unique Network Addresses Associated With It. Basic Security Settings Should Be Established On Any Router Before It Is Connected To An Operational Network.
If One Is Dealing Only With A Local Area Network (LAN), There Is Generally No Need For Routing, Routers, TCP/IP, Or IP Addresses. Within A LAN Everything Will Be Handled By Media Access Control (MAC) Addresses And By A LAN Protocol Such As Ethernet. At This Level, Most Protocols Are Defined By Institute Of Electrical And Electronics Engineers (IEEE) Standards. For Instance, IEEE 802.3 Is The Ethernet (CSMA/CD) Standard, 802.4 Is Token Bus, And 802.5 Is Token Ring. Above The MAC Standards, But Still Within The OSI Data Link Layer, Is The IEEE 802.2 Logical Link Control Standard.
What Is Important To Keep In Mind Is That MAC Addresses Are Used Within A LAN. Each Device On The LAN Will Have A Something Like A Network Interface Card (NIC) Which Has A Unique MAC Address.
Ethernet MAC Addresses Are 48 Bits Long. They Are Assigned By The Device (Or Interface Card) Manufacturer. Each Address Is Unique And Fixed To A Particular Piece Of Hardware. (On Some Newer Devices It Is Possible To Change Them But Normally This Should Not Be Done.) As Stated Previously, MAC Addresses Are Used Within A LAN By Layer Two (Data Link) Protocols. Traditionally, 24 Bits Uniquely Identify The Manufacturer And 24 Bits Act As A Serial Number To Uniquely Identify The Unit. Some Manufacturers Have Had More Than One Identification Number (More Than One Block Of Serial Numbers). Also, Due To Mergers And Acquisitions The Manufacturer Identification Is Not As “Clean” As It Once Was. Still, All Network Interface Devices Have Globally Unique Addresses Unless Their Proms Have Been Rewritten.
Under The Current IP Version 4 Standard, IP Addresses Are 32 Bits Long. They Are Used By Layer Three Devices Such As Routers. Unlike MAC Addresses, IP Addresses Are Hierarchical. IP Version 4 (IPv4) Uses 32-Bit Numbers That Combine A Network Address And Host Address. IP Addresses Are Written In Four Decimal Fields Separated By Periods. Each Number Represents A Byte. The Far Right Bits Are The Network Address Because All Hosts On This Network Have Addresses That Start With That Pattern. The Left Bits Are The Host Address Because Each Host Has A Different Value. A Sample IP Address Might Look Like 192.168.1.5/24.
IP ADDRESS AND CLASS FACTS: IP ADDRESSES ALLOW HOSTS TO PARTICIPATE ON IP BASED NETWORKS. AN IP ADDRESS:
✓ Is A 32-Bit Binary Number Represented As Four Octets (Four 8-Bit Values). Each Octet Is Separated By A Period.
✓ IP Addresses Can Be Represented In One Of Two Ways:
◙ - ➤ Decimal (For Example 131.107.2.200). In Decimal Notation, Each Octet Must Be Between 0 And 255.
◙ - ➤ Binary (For Example 10000011.01101011.00000010.11001000). In Binary Notation,Each Octet Is An 8-Digit Number.
✓ The IP Address Includes Both The Network And The Host Address.
✓ Each IP Address Has An Implied Address Class That Can Be Used To Infer The Network Portion Of The Address.
✓ The Subnet Mask Is A 32-Bit Number That Is Associated With Each IP Address That Identifies The Network Portion Of The Address. In Binary Form, The Subnet Mask Is Always A Series Of 1's Followed By A Series Of 0's (1's And 0's Are Never Mixed In Sequence In The Mask). A Simple Mask Might Be 255.255.255.0.
IP ADDRESSES HAVE A DEFAULT CLASS. THE ADDRESS CLASS IDENTIFIES THE RANGE OF IP ADDRESSES AND A DEFAULT SUBNET MASK USED FOR THE RANGE ;
◙ CLASS A Address Range: 1.0.0.0 to 126.255.255.255, First Octet Range 1-126 (00000001--01111110 binary), Default Subnet Mask 255.0.0.0
◙ CLASS B Address Range: 128.0.0.0 to 191.255.255.255, First Octet Range 128-191(10000000--10111111 binary) Default Subnet Mask 255.255.0.0
◙ CLASS C Address Range: 192.0.0.0 to 223.255.255.255, First Octet Range 192-223 (11000000--11011111 binary) Default Subnet Mask 255.255.255.0
◙ CLASS D Address Range: 224.0.0.0 to 239.255.255.255, First Octet Range 224-239 (11100000--11101111 binary) Default Subnet Mask N/A
◙ CLASS E Address Range: 240.0.0.0 to 255.255.255.255, First Octet Range 240-255 (11110000--11111111 binary) Default Subnet MaskN/A
WHEN USING THE DEFAULT SUBNET MASK FOR AN IP ADDRESS, YOU HAVE THE FOLLOWING NUMBER OF SUBNET ADDRESSES AND HOSTS PER SUBNET:
◙ - ➤ There Are Only 126 Class A Network Ids (Most Of These Addresses Are Already Assigned) Each Class A Address Gives You 16,777,214 Hosts Per Network.
◙ - ➤ There Are 16,384 Class B Network Ids. Each Class B Address Gives You 65,534 Hosts Per Network.
◙ - ➤ There Are 2,097,152 Class C Network Ids. Each Class C Address Gives You 254 Hosts Per Network.
◙ - ➤ Class D Addresses Are Used For Multicast Groups Rather Than Network And Host Ids.
◙ - ➤ Class E Addresses Are Reserved For Experimental Use.
THE FOLLOWING ADDRESS RANGES HAVE BEEN RESERVED FOR PRIVATE USE:
◙ - ➤ 10.0.0.0 To 10.255.255.255
◙ - ➤ 172.16.0.0 To 172.31.255.255
◙ - ➤ 192.168.0.0 To 192.168.255.255
Use Addresses In These Ranges For Your Private Networks. Routers Connected To The Internet Typically Filter Messages Within These Ranges And Prevent Them From Being Propagated To The Internet.
LOCAL HOST ADDRESS: Addresses In The 127.0.0.0 Range Are Reserved For The Local Host (In Other Words "This"Host Or The Host You're Currently Working At). The Most Commonly-Used Address Is 127.0.0.1 Which Is The Loopback Address.
BROADCAST ADDRESS: The Last Address In The Range Is Used As The Broadcast Address And Is Used To Send Messages To All Hosts On The Network. In Binary Form, The Broadcast Address Has All 1's In The Host Portion Of The Address.
FOR EXAMPLE, ASSUMING THE DEFAULT SUBNET MASKS ARE USED:
◙ - ➤ 115.255.255.255 Is The Broadcast Address For Network 115.0.0.0
◙ - ➤ 154.90.255.255 Is The Broadcast Address For Network 154.90.0.0
◙ - ➤ 221.65.244.255 Is The Broadcast Address For Network 221.65.244.0
TWO OTHER FORMATS YOU MIGHT SEE FOR THE BROADCAST ADDRESS:
◙ - ➤ The Broadcast Address Might Also Be Designated By Setting Each Of The Network Address Bits To 0. For Example, 0.0.255.255 Is The Broadcast Address Of A Class B Address. This Designation Means "The Broadcast Address For This Network."
◙ - ➤ 255.255.255.255 Indicates A Broadcast Message Intended For All Hosts On This Network.
The Open Systems Interconnection (OSI) Reference Model (ISO 7498) Defines A Seven-Layer Model Of Data Communication With Physical Transport At The Lower Layer And Application Protocols At The Upper Layers.
Each Layer Provides A Set Of Functions To The Layer Above And, In Turn, Relies On The Functions Provided By The Layer Below. Although Messages Can Only Pass Vertically Through The Stack From Layer To Layer, From A Logical Point Of View, Each Layer Communicates Directly With Its Peer Layer On Other Nodes.
THE SEVEN LAYERS ARE:
◙ - ➤ Layer 7: Application Layer - > Deals with Network Applications Such As Terminal Emulation and File Transfer
◙ - ➤ Layer 6: Presentation Layer - > Deals With Formatting, Encryption, And Compression Of Data.
◙ - ➤ Layer 5: Session Layer - > Deals With Setup And Management Of Sessions Between Applications.
◙ - ➤ Layer 4: Transport Layer - > Deals With End To End Error Recovery And Delivery Of Complete Messages.
◙ - ➤ Layer 3: Network Layer - > Deals With Transmission Of Packets And Establishing Connections.
◙ - ➤ Layer 2: Data Link Layer - > Framing Of Units Of Information And Error Checking
◙ - ➤ Layer 1: Physical Layer - > Deals With Transmission Of A Bit Stream And Definition Of Physical Link.
Groups Of Protocols (Called Protocol Suites Or Protocol Stacks) Are Designed To Interact And Be Used Together. The TCP/IP Protocol Suite Is Used On The Internet And On Most Networks. Nearly All Computers Today Use TCP/IP Protocols For Communication Because It Is Highly Scalable And Routable. The Layers Of The DOD Model Are As Follows:
◙ - ➤ The Application Layer (Also Called The Process Layer) Corresponds To The Session, Presentation, And Application Layers Of The OSI Model.
◙ - ➤ The Host-To-Host Layer Is Comparable To The Transport Layer Of The OSI Model And Is Responsible For Error Checking And Reliable Packet Delivery. Here, The Data Stream Is Broken Into Segments That Must Be Assigned Sequence Numbers So That The Segments Can Be Reassembled Correctly On The Remote Side After They Are Transported.
◙ - ➤ The Internet Layer Is Comparable To The Network Layer Of The OSI Model. It Is Responsible For Moving Packets Through A Network. This Involves Addressing Of Hosts And Making Routing Decisions To Identify How The Packet Transverses The Network.
◙ - ➤ The Network Access Layer Corresponds To The Functions Of The Physical And Data Link Layers Of The OSI Model. It Is Responsible For Describing The Physical Layout Of The Network And How Messages Are Formatted On The Transmission Medium. Sometimes This Layer Is Divided Into The Network Access And The Physical Layer.
Note: The TCP/IP Model Focuses Specifically On The Functions In The Internet Layer And The Host-To-Host Layer.
DEVICE COMMUNICATION:
Data Encapsulation Facts, Encapsulation Is The Process Of Breaking A Message Into Packets, Adding Control And Other Information, And Transmitting The Message Through The Transmission Media.
THE FOLLOWING FIVE-STEP DATA ENCAPSULATION PROCESS:
◙ - ➤ 1. Upper Layers Prepare The Data To Be Sent Through The Network.
◙ - ➤ 2. The Transport Layer Breaks The Data Into Pieces Called Segments, Adding Sequencing And Control Information.
◙ - ➤ 3. The Network Layer Converts The Segments Into Packets, Adding Logical Network And Device Addresses.
◙ - ➤ 4. The Data Link Layer Converts The Packets Into Frames, Adding Physical Device Addressing Information.
◙ - ➤ 5. The Physical Layer Converts The Frames Into Bits For Transmission Across The Transmission Media.
THE FOLLOWING SHORT DESCRIPTIONS CAN HELP YOU REMEMBER THE STEPS OF THE DATA ENCAPSULATION PROCESS:
◙ - ➤ Upper Layers -- > Data
◙ - ➤ Transport Layer -- >Segments
◙ - ➤ Network Layer -- > Packets Containing Logical Addresses
◙ - ➤ Data Link Layer -- > Framing That Adds Physical Addresses
◙ - ➤ Physical Layer -- > Bits
Devices On A LAN Must Also Be Uniquely And Individually Identified Or They, Like Humans Sharing The Same Name, Will Receive Data Not Intended For Them. When Data Is To Be Delivered On A LAN, It Is Encapsulated Within An Entity Called A Frame, A Kind Of Binary Envelope. Think Of Data Encapsulation As Being The Digital Equivalent Of Placing A Letter Inside An Envelope. A Destination Address And A Return (Source) Address Are Written On The Outside Of The Envelope. Without A Destination Address, The Postal Service Would Have No Idea Where To Deliver The Letter. Likewise, When A Frame Is Placed On A Data Link, All Devices Attached To The Link "See" The Frame; Therefore, Some Mechanism Must Indicate Which Device Should Pick Up The Frame And Read The Enclosed Data.
Is A Specialized Network That Enables Fast, Reliable Access Among Servers And External Storage Resources.
WHICH Two Primary Port Authentication Protocols Are Used With VSANs?
Tips: (Virtual Storage Area Network (VSAN) Is A Collection Of Ports From A Set Of Connected Fibre Channel Switches, That Form A Virtual Fabric. Ports Within A Single Switch Can Be Partitioned Into Multiple VSANs, Despite Sharing Hardware Resources. Conversely, Multiple Switches Can Join A Number Of Ports To Form A Single VSAN. VSANs Were Designed By Cisco Systems, Modelled After The Virtual Local Area Network (VLAN) Concept In Ethernet Networking, Applied To A Storage Area Network. In October 2004, The Technical Committee T11 Of The International Committee For Information Technology Standards Approved VSAN Technology To Become A Standard Of The American National Standards Institute (ANSI)).
CHAP And DHCHAP Two primary port authentication protocols when working with VSANs:
CHALLENGE HANDSHAKE AUTHENTICATION PROTOCOL (CHAP):
CHAP Is The Mandatory Protocol For iSCCI (Internet Small Computer System Interface, An Internet Protocol (IP)-Based Storage Networking Standard For Linking Data Storage Facilities), As Chosen By The Internet Engineering Task Force (IETF). CHAP Is Based On Shared Secrets.
Diffie-HELLMAN CHALLENGE HANDSHAKE AUTHENTICATION PROTOCOL (DHCHAP):
DHCHAP May Be Used To Authenticate Devices Connecting To A Fibre Channel Switch. By Using Fibre Channel Authentication, You Allow Only Trusted Devices To Be Added To A Fabric. This Prevents Unauthorized Devices From Accessing The Fibre Channel Switch.
1. PRIMARY PURPOSE OF A LAN?
Answer: The Primary Purpose Of A Local-Area Network Is To Allow Resource Sharing. The Resources May Be Devices, Applications, Or Information. Examples Of Shared Resources Are Files, Databases, E-Mail, Modems, And Printers.
2. PROTOCOL?
Answer: A Protocol Is An Agreed-Upon Set Of Rules. In Data Communications, The Rules Usually Govern A Procedure Or A Format.
3. PURPOSE OF A MAC PROTOCOL?
Answer: A Media Access Control Protocol Defines How A Given LAN Medium Is Shared, How LAN Devices Connected To The Medium Are Identified, And How Frames Transmitted Onto The Medium Are Formatted.
4. FRAME?
Answer: A Frame Is A Digital "Envelope" That Provides The Information Necessary For The Delivery Of Data Across A Data Link. Typical Components Of A Frame Are Identifiers (Addresses) Of The Source And Destination Devices On The Data Link, An Indicator Of The Type Of Data Enclosed In The Frame, And Error-Checking Information.
5. WHAT FEATURE IS COMMON TO ALL FRAME TYPES?
Answer: A Feature Common To All Frame Types Is A Format For Identifying Devices On The Data Link.
6. MAC ADDRESS / MAC IDENTIFIER?
Answer: A Media Access Control Address Or Identifier Is A Means By Which Individual Devices Connected To A Data Link Are Uniquely Identified For The Purpose Of Delivering Data.
7. WHY IS A MAC ADDRESS NOT A TRUE ADDRESS?
Answer: An Address Specifies A Location. A MAC Address Is Not A True Address Because It Is Permanently Associated With The Interface Of A Specific Device And Moves Whenever The Device Moves. A MAC Identifies The Device, Not The Location Of The Device.
8. WHAT ARE THE THREE SOURCES OF SIGNAL DEGRADATION ON A DATA LINK?
Answer: The Three Sources Of Signal Degradation On A Data Link Are Attenuation, Interference, And Distortion.
Attenuation Is A Function Of The Resistance Of The Medium.
Interference Is A Function Of Noise Entering The Medium.
Distortion Is A Function Of The Reactive Characteristics Of The Medium, Which React Differently To Different Frequency Components Of The Signal.
9. PURPOSE OF A REPEATER?
Answer: A Repeater Is A Device That Extends The Useful Range Of A Physical Medium By Reading A Degraded Signal And Producing A "Clean" Copy Of The Signal.
10. PURPOSE OF A BRIDGE?
Answer: A Bridge Is A Device That Increases The Capacity Of A LAN. A Bridge Divides The Data Link Into Segments, Forwarding Only Traffic That Is Generated On One Segment And Is Destined For Another Segment. By Controlling And Limiting The Traffic On A Data Link, More Devices May Be Attached To The LAN.
11. WHAT MAKES A TRANSPARENT BRIDGE TRANSPARENT?
Answer: A Transparent Bridge "Listens Promiscuously" On Each Of Its Ports. That Is, It Examines All Frames On All Media To Which It Is Attached. It Records The Source MAC Identifiers Of The Frames, And The Ports On Which It Learns The Identifiers, In A Bridging Table.
It Can Then Refer To The Table When Deciding Whether To Filter Or Forward A Frame. The Bridge Is Transparent Because It Performs This Learning Function Independently Of The Devices That Originate The Frames. The End Devices Themselves Have No Knowledge Of The Bridge.
12. DIFFERENCES BETWEEN LANS AND WANS:
Answer: Three Fundamental Differences Between Local-Area And Wide-Area Networks Are:
LANs Are Limited To A Small Geographic Area, Such As A Single Building Or Small Campus.
WANs Cover A Large Geographic Area, From Citywide To Worldwide.
LANs Usually Consist Entirely Of Privately Owned Components. Some Components Of A WAN, Such As A Packet Switching Network Or Point-To-Point Serial Links, Are Usually Leased From A Service Provider.
A LAN Provides High Bandwidth At A Relatively Cheap Price. The Bandwidth Across A WAN Is Significantly More Expensive.
13. WHAT IS THE PURPOSE OF A BROADCAST MAC IDENTIFIER? WHAT IS THE BROADCAST MAC IDENTIFIER, IN HEX AND IN BINARY?
Answer: A Broadcast MAC Identifier, When Used As The Destination Address Of A Frame, Signifies That The Data Is For All Devices Attached To The Data Link. In Binary, The Broadcast MAC Identifier Is All Ones. In Hex, It Is Ffff.Ffff.Ffff.
14. PRIMARY SIMILARITY AND DIFFERENCE BETWEEN A BRIDGE AND A ROUTER?
Answer: The Primary Similarity Between A Bridge And A Router Is That Both Devices Increase The Number Of Hosts That May Be Interconnected Into A Common Communications Network.
The Difference Is That A Bridge Works By Interconnecting Separate Segments Of A Single Network, Whereas A Router Interconnects Separate Networks.
15. WHAT IS A PACKET? WHAT IS THE PRIMARY SIMILARITY AND DIFFERENCE BETWEEN A FRAME AND A PACKET?
Answer: A Packet Is The Means By Which Data Is Transported From One Network To Another.
The Similarity Between A Frame And A Packet Is That They Both Encapsulate Data And Provide An Addressing Scheme For Delivering The Data.
The Difference Between A Frame And A Packet Is That The Frame Delivers Data Between Two Devices Sharing A Common Data Link, Whereas A Packet Delivers Data Across A Logical Pathway, Or Route, Spanning Multiple Data Links.
16. AS A PACKET PROGRESSES ACROSS AN INTERNETWORK, DOES THE SOURCE ADDRESS CHANGE?
Answer: Neither The Source Nor The Destination Address Of A Packet Changes As It Progresses From The Source Of The Packet To The Destination.
17. WHAT IS A NETWORK ADDRESS? WHAT IS THE PURPOSE OF EACH PART OF A NETWORK ADDRESS? Answer: Network Addresses Are The Addresses Used In Packets. Each Network Address Has A Network Part, Which Identifies A Particular Data Link, And A Host Or Node Part, Which Identifies A Specific Device On The Data Link Identified By The Network Part.
18. PRIMARY DIFFERENCE BETWEEN A NETWORK ADDRESS AND A DATA LINK IDENTIFIER?
Answer: A Packet Identifies A Device From The Perspective Of The Entire Internetwork. A Frame Identifies A Device From The Perspective Of A Single Data Link. Because The Connection Between Two Devices Across An Internetwork Is A Logical Path, A Network Address Is A Logical Address. Because The Connection Between Two Devices Across A Data Link Is A Physical Path, A Data Link Identifier Is A Physical Address.
19. OPEN SYSTEMS INTERCONNECTION (OSI) SEVEN LAYER AND PURPOSE OF EACH LAYER?
Answer:
LAYER 7: Application Layer - ➤ Deals With Services Such As Email And File Transfer.
LAYER 6: Presentation Layer - ➤ Deals With Formatting, Encryption, And Compression Of Data.
LAYER 5: Session Layer- ➤ Deals With Setup And Management Of Sessions Between Applications.
Layer 4: Transport Layer - ➤ Deals With End To End Error Recovery And Delivery Of Complete Messages.
LAYER 3: Network Layer - ➤ Deals With Transmission Of Packets And Establishing Connections.
LAYER 2: Data Link Layer -- ➤ Deals With Transmission Of Packets On One Given Physical Link. How The Medium Is Accessed And Shared, How Devices On The Medium Are Identified, And How Data Is Framed Before Being Transmitted On The Medium.
LAYER 1: Physical Layer - ➤ Deals With Transmission Of A Bit Stream And Definition Of Physical Link.
Also The Five Layers Of The TCP/IP Protocol Suite Are The Following:
✓ Physical Layer - > The Physical Layer Contains The Protocols Of The Physical Medium.
✓ Data-Link Layer - > The Data Link Layer Contains The Protocols That Control The Physical Layer: How The Medium Is Accessed And Shared, How Devices On The Medium Are Identified, And How Data Is Framed Before Being Transmitted On The Medium.
✓ Internet (Or IP) Layer - > The Internet Layer Contains The Protocols That Define The Logical Grouping Of Data Links Into A Network And The Communication Across That Network.
✓ Host-To-Host Layer - > The Host-To-Host Layer Contains The Protocols That Define And Control The Logical, End-To-End Paths Across The Network.
✓ Application Layer - > The Application Layer Corresponds To The OSI Session, Presentation, And Application Layers.
20. MOST COMMON IP VERSION PRESENTLY IN USE?
Answer: The Most Common IP Version Now In Use Is Version 4(IPv4).
21. WHAT IS FRAGMENTATION? WHAT FIELDS OF THE IP HEADER ARE USED FOR FRAGMENTATION?
Answer: Routers Perform Fragmentation When A Packet Is Longer Than The Maximum Packet Length (Maximum Transmission Unit, Or MTU) Supported By A Data Link Onto Which The Packet Must Be Transmitted.
The Data Within The Packet Will Be Broken Into Fragments, And Each Fragment Will Be Encapsulated In Its Own Packet. The Receiver Uses The Identifier And Fragment Offset Fields And The MF Bit Of The Flags Field To Reassemble The Fragments.
22. PURPOSE OF THE TTL FIELD IN THE IP HEADER? HOW DOES THE TTL PROCESS WORK?
Answer: The TIME TO LIVE (TTL) Field Prevents "Lost" Packets From Being Passed Endlessly Through The IP Internetwork. The Field Contains An 8-Bit Integer That Is Set By The Originator Of The Packet.
Each Router Through Which The Packet Passes Will Decrement The Integer By One. If A Router Decrements The TTL To Zero, It Will Discard The Packet And Send An ICMP "Time Exceeded" Error Message To The Packet's Source Address.
23. WHAT IS THE FIRST OCTET RULE?
Answer: The First Octet Rule Determines The Class Of An IP Address As Follows:
Class A: The First Bit Of The First Octet Is Always 0.
Class B: The First Two Bits Of The First Octet Are Always 10.
Class C: The First Three Bits Of The First Octet Are Always 110.
Class D: The First Four Bits Of The First Octet Are Always 1110.
Class E: The First Four Bits Of The First Octet Are Always 1111.
24. HOW ARE CLASS A, B, AND C IP ADDRESSES RECOGNIZED IN DOTTED DECIMAL? HOW ARE THEY RECOGNIZED IN BINARY?
Answer: The A, B, C IP Addresses Are Recognized In Dotted Decimal And Binary As Follows:
Class Binary Range Of First Octet Decimal Range Of First Octet
A 0000000 - 01111110 1 - 126
B 10000000 - 10111111 128 - 191
C 11000000 - 11011111 192- 223
25. AN ADDRESS MASK, AND HOW DOES IT WORK?
Answer: An IP Address Mask Identifies The Network Part Of An IP Address. Each One In The 32-Bit Mask Marks The Corresponding Bit In The IP Address As A Network Bit. A Zero In The Mask Marks The Corresponding Bit In The IP Address As A Host Bit. A Boolean AND Is Performed In All 32 Bits Of The Address And The Mask; In The Result, All Network Bits Of The Mask Will Be Repeated, And All Host Bits Will Be Changed To Zero.
26. WHAT IS A SUBNET? WHY ARE SUBNETS USED IN IP ENVIRONMENTS?
Answer: A Subnet Is A Sub Grouping Of A Class A, B, Or C IP Address. Without Subnetting, The Network Part Of A Major Class A, B, Or C IP Address Can Only Identify A Single Data Link. Subnetting Uses Some Of The Host Bits Of A Major IP Address As Network Bits, Allowing The Single Major Address To Be "Subdivided" Into Multiple Network Addresses.
27. WHY CAN'T A SUBNET OF ALL ZEROS OR ALL ONES BE USED IN A CLASSFUL ROUTING ENVIRONMENT?
Answer: A Classful Routing Protocol Has No Way To Differentiate Between The All-Zeroes Subnet And The Major IP Address, And Between The All-Ones Subnet And The All-Hosts, All-Subnets Broadcast Address Of The Major IP Address.
28. WHAT IS ARP?
Answer: Address Resolution Protocol (ARP), Is A Function That Maps The IP Addresses Of Interfaces On A Data Link To Their Corresponding MAC Identifiers.
29. WHAT IS PROXY ARP?
Answer: Proxy ARP Is A Function Of An IP Router. If The Router Hears An ARP Request, And The Destination Network Or Subnet Is In The Router's Routing Table, And The Table Indicates That The Destination Is Reachable Via A Different Router Interface Than The One On Which The ARP Request Was Received, The Router Will Respond To The ARP Request With Its Own MAC Address.
30. WHAT IS A REDIRECT?
Answer: A Redirect Is An IP Router Function. If A Device Has Sent A Packet To The Router And The Router Must Forward The Packet To A Next-Hop Router On The Same Data Link, The Router Will Send A Redirect To The Originating Device. The Redirect Will Inform The Device That It Can Reach The Next-Hop Router Directly.
31. WHAT IS THE ESSENTIAL DIFFERENCE BETWEEN TCP AND UDP?
Answer:
TCP, Or Transmission Control Protocol, Provides A Connection-Oriented Service Over The Connectionless Internet Layer.
UDP, Or User Datagram Service, Provides A Connectionless Service.
32. WHAT MECHANISMS DOES TCP USE TO PROVIDE CONNECTION-ORIENTED SERVICE?
Answer: Correct Sequencing Is Accomplished With Sequence Numbers. Reliability Is Accomplished By Using Checksums, Acknowledgments, Timers, And Retransmissions. Flow Control Is Accomplished By Windowing.
33. INSTEAD OF ARP, NOVELL NETWARE USES A NETWORK ADDRESS THAT INCLUDES A DEVICE'S MAC ADDRESS AS THE HOST PORTION. WHY CAN'T IP DO THIS?
Answer: A MAC Identifier Is A Fixed-Length Binary Integer. If IP Used MAC Identifiers As The Host Part Of The IP Address, Subnetting Would Not Be Possible Because There Would Be No Flexibility In Using Some Of The Host Bits As Network Bits.
34. Netware Has A Transport Layer Service Similar To TCP Called Sequenced Packet Exchange (SPX), But No Service Similar To UDP. Applications Requiring Connectionless Service Directly Access The Connectionless IPX At The Network Layer. --- WHAT PURPOSE DOES UDP SERVE BY PROVIDING A CONNECTIONLESS SERVICE ON TOP OF WHAT IS ALREADY A CONNECTIONLESS SERVICE?
Answer: The Only Purpose Of The UDP Header Is To Add Fields For The Source And Destination Port Numbers.
35. WHAT INFORMATION MUST BE STORED IN THE ROUTE TABLE?
Answer: At A Minimum, Each Entry Of The Routing Table Must Include A Destination Address And The Address Of A Next-Hop Router Or An Indication That The Destination Address Is Directly Connected.
36. WHAT DOES IT MEAN WHEN A ROUTE TABLE SAYS THAT AN ADDRESS IS VARIABLY SUBNETTED?
Answer: Variably Subnetted Means That The Router Knows Of More Than One Subnet Mask For Subnets Of The Same Major IP Address.
37. WHAT ARE DISCONTIGUOUS SUBNETS?
Answer: Discontiguous Subnets Are Two Or More Subnets Of A Major IP Network Address That Are Separated By A Different Major IP Address.
Routing Is The Process Of Selecting Best Paths In A Network. In The Past, The Term Routing Was Also Used To Mean Forwarding Network Traffic Among Networks.
◙ Routing Is The Act Of Moving Information Across A Network (With At Least One Node In Between.)
◙ Routing Occurs At Layer 3 Of The OSI Model (Network Layer).
◙ Routing Involves Two Basic Activities:
A. Determining Optimal Routing Paths
✓ Protocol Use Metrics For Evaluation Of Paths
✓ Routing Algorithms Initialize And Maintain Routing Tables (Contain Route Information)
B. Transporting Information Groups (Packets)
Routing Protocols Are Used In The Implementation Of Routing Algorithms To Facilitate The Exchange Of Routing Information Between Networks, Allowing Routers To Build Routing Tables Dynamically. In Some Cases, Routing Protocols Can Themselves Run Over Routed Protocols: For Example, BGP Runs Over TCP: Care Is Taken In The Implementation Of Such Systems Not To Create A Circular Dependency Between The Routing And Routed Protocols.
Routing Protocals Are:
✓ ROUTING INFORMATION PROTOCOL (RIP AND RIP II)
✓ OPEN SHORTEST PATH FIRST (OSPF)
✓ INTERMEDIATE SYSTEM TO INTERMEDIATE SYSTEM (IS-IS)
✓ INTERIOR GATEWAY ROUTING PROTOCOL (IGRP)
✓ CISCO'S ENHANCED INTERIOR GATEWAY ROUTING PROTOCOL (EIGRP)
✓ BORDER GATEWAY PROTOCOL (BGP).
A Routed Protocol Is Any Network Layer Protocol That Provides Enough Information In Its Network Layer Address To Allow A Packet To Be Forwarded From One Host To Another Host Based On The Addressing Scheme, Without Knowing The Entire Path From Source To Destination. Routed Protocols Define The Format And Use Of The Fields Within A Packet. Packets Generally Are Conveyed From End System To End System. Almost All Network Layer Protocols And Those That Are Layered Over Them Are Routable, With IP Being An Example.
Data Link Protocols Such As Ethernet Are Necessarily Non-Routable Protocols, Since They Contain Only A Link-Layer Address, Which Is Insufficient For Routing: Some Higher-Level Protocols Based Directly On These Without The Addition Of A Network Layer Address, Such As 'Netbios', Are Also Non-Routable.
A Routing Metric Consists Of Any Value Used By Routing Algorithms To Determine To Choose One Route Over Another. Metrics Can Take Into Account Such Information As Bandwidth, Delay, Hop Count, Load, MTU, Reliability, And Cost. The Routing Table Stores Only The Best Possible Routes, While Link-State Or Topological Databases May Store All Other Information As Well.
Routers Use The Feature Known As Administrative Distance To Select The Best Path When They "Know" Of Two Or More Different Routes To The Same Destination From Two Different Routing Protocols. Administrative Distance Defines The Reliability Of A Routing Protocol. Each Routing Protocol Gets Prioritized In Order Of Most To Least Reliable Using An Administrative-Distance Value. A Static Route Has A Lower (Better) Administrative-Distance Than A Route By OSPF, Which Is Better Than RIP.
38. WHAT COMMAND IS USED TO EXAMINE THE ROUTE TABLE IN A CISCO ROUTER?
Answer: Show IP Route Is Used To Examine The Routing Table Of A Cisco Router.
39. WHAT ARE THE TWO BRACKETED NUMBERS ASSOCIATED WITH THE NON-DIRECTLY CONNECTED ROUTES IN THE ROUTE TABLE?
Answer: The First Bracketed Number Is The Administrative Distance Of The Routing Protocol By Which The Route Was Learned. The Second Number Is The Metric Of The Route.
40. WHEN STATIC ROUTES ARE CONFIGURED TO REFERENCE AN EXIT INTERFACE INSTEAD OF A NEXT-HOP ADDRESS, IN WHAT WAY WILL THE ROUTE TABLE BE DIFFERENT?
Answer: When A Static Route Is Configured To Reference An Exit Interface Instead Of A Next-Hop Address, The Destination Address Will Be Entered Into The Routing Table As Directly Connected.
41. WHAT IS A SUMMARY ROUTE? IN THE CONTEXT OF STATIC ROUTING, HOW ARE SUMMARY ROUTES USEFUL?
Answer: A Summary Route Is A Single Route Entry That Points To Multiple Subnets Or Major IP Addresses. In The Context Of Static Routes, Summary Routes Can Reduce The Number Of Static Routes That Must Be Configured.
42. WHAT IS AN ADMINISTRATIVE DISTANCE?
Answer: An Administrative Distance Is A Rating Of Preference For A Routing Protocol Or A Static Route. Every Routing Protocol And Every Static Route Has An Administrative Distance Associated With It. When A Router Learns Of A Destination Via More Than One Routing Protocol Or Static Route, It Will Use The Route With The Lowest Administrative Distance.
43. WHAT IS A FLOATING STATIC ROUTE?
Answer: A Floating Static Route Is An Alternative Route To A Destination. The Administrative Distance Is Set High Enough That The Floating Static Route Is Used Only If A More-Preferred Route Becomes Unavailable.
44. WHAT IS THE DIFFERENCE BETWEEN EQUAL-COST AND UNEQUAL-COST LOAD SHARING?
Answer:
✓ Equal-Cost Load Sharing Distributes Traffic Equally Among Multiple Paths With Equal Metrics.
✓ Unequal-Cost Load Sharing Distributes Packets Among Multiple Paths With Different Metrics. The Traffic Will Be Distributed Inversely Proportional To The Cost Of The Routes.
45. HOW DOES THE SWITCHING MODE AT AN INTERFACE AFFECT LOAD SHARING?
Answer: If An Interface Is Fast Switched, Per Destination Load Sharing Is Performed. If An Interface Is Process Switched, Per Packet Load Sharing Is Performed.
46. WHAT IS A RECURSIVE TABLE LOOKUP?
Answer: A Recursive Routing Table Lookup Occurs When A Router Cannot Acquire All The Information It Needs To Forward A Packet With A Single Routing Table Lookup.
For Example, The Router May Perform One Lookup To Find The Route To A Destination And Then Perform Another Lookup To Find A Route To The Nexthop Router Of The First Route.
47. WHAT IS A ROUTING PROTOCOL?
Answer: A Routing Protocol Is A "Language" That Routers Speak To Each Other To Share Information About Network Destinations.
48. WHAT BASIC PROCEDURES SHOULD A ROUTING ALGORITHM PERFORM?
Answer: At A Minimum, A Routing Protocol Should Define Procedures For:
✓ Passing Reachability Information About Networks To Other Routers,
✓ Receiving Reachability Information From Other Routers, Determining Optimal Routes Based On The Reachability Information It Has And For Recording This Information In A Route Table Reacting To, Compensating For, And Advertising Topology Changes In An Internetwork.
49. WHY DO ROUTING PROTOCOLS USE METRICS?
Answer: A Route Metric, Also Called A Route Cost Or A Route Distance, Is Used To Determine The Best Path To A Destination. Best Is Defined By The Type Of Metric Used.
50. WHAT IS CONVERGENCE TIME?
Answer: Convergence Time Is The Time A Group Of Routers Take To Complete The Exchange Of Routing Information.
51. WHAT IS LOAD BALANCING? NAME FOUR DIFFERENT TYPES OF LOAD BALANCING.
Answer: Load Balancing Is The Process Of Sending Packets Over Multiple Paths To The Same Destination. Four Types Of Load Balancing Are:
✓ Equal Cost, Per Packet
✓ Equal Cost, Per Destination
✓ Unequal Cost, Per Packet
✓ Unequal Cost, Per Destination
52. WHAT IS A DISTANCE VECTOR ROUTING PROTOCOL?
Answer: A Distance Vector Protocol Is A Routing Protocol In Which Each Router Calculates Routes Based On The Routes Of Its Neighbors And Then Passes Its Routes To Other Neighbors.
53. NAME SEVERAL PROBLEMS ASSOCIATED WITH DISTANCE VECTOR PROTOCOLS.
Answer: Several Problems Associated With Distance Vector Protocols Are:
A Susceptibility To Incorrect Routing Information Because Of Its Dependence On Neighbors For - >
✓ Correct Information
✓ Slow Convergence
✓ Route Loops
✓ Counting To Infinity
54. WHAT ARE NEIGHBORS?
Answer: Neighbors Are Routers Connected To The Same Data Link.
55. WHAT IS THE PURPOSE OF ROUTE INVALIDATION TIMERS?
Answer: Route Invalidation Timers Delete Routes From A Route Table If They Exceed A Certain Age.
56. EXPLAIN THE DIFFERENCE BETWEEN SIMPLE SPLIT HORIZON AND SPLIT HORIZON WITH POISONED REVERSE.
Answer:
✓ Simple Split Horizon Does Not Send Route Information Back To The Source Of The Route Information.
✓ Split Horizon With Poisoned Reverse Sends The Information Back To The Source But Sets The Metric To Unreachable.
57. WHAT IS THE COUNTING-TO-INFINITY PROBLEM, AND HOW CAN IT BE CONTROLLED?
Answer: Counting To Infinity Occurs When Routes Update A Route Over A Loop; Each Router Increases The Metric Of The Route Until The Metric Reaches Infinity. The Effects Of Counting To Infinity Are Controlled By Defining Infinity As A Fairly Low Metric So That Infinity Is Reached Fairly Quickly And The Route Is Declared Unreachable.
58. WHAT ARE HOLDDOWN TIMERS, AND HOW DO THEY WORK?
Answer: Holddown Timers Help Prevent Routing Loops. If A Route Is Declared Unreachable Or If The Metric Increases Beyond A Certain Threshold, A Router Will Not Accept Any Other Information About That Route Until The Holddown Timer Expires.
This Approach Prevents The Router From Accepting Possibly Bad Routing Information While The Internetwork Is Reconverging.
59. WHAT ARE THE DIFFERENCES BETWEEN DISTANCE VECTOR AND LINK STATE ROUTING PROTOCOLS?
Answer:
✓ A Distance Vector Router Sends Its Entire Route Table, But It Only Sends The Table To Directly Connected Neighbors.
Distance Vector Protocols Usually Use A Variant Of The Bellman-Ford Algorithm To Calculate Routes,
✓ A Link State Router Sends Only Information About Its Directly Connected Links, But It Floods The Information Throughout The Internetworking Area.
And Link State Protocols Usually Use A Variant Of The Dijkstra Algorithm To Calculate Routes.
60. WHAT IS THE PURPOSE OF A TOPOLOGICAL DATABASE?
Answer: A Topological Database Holds The Link State Information Originated By All Routers In The Link State Routing Domain.
61. EXPLAIN THE BASIC STEPS INVOLVED IN CONVERGING A LINK STATE INTERNETWORK?
Answer:
✓ Each Router Floods A Link State Information Advertisement Describing Its Links, The States Of Its Links, And Any Neighboring Routers Connected To Those Links, Throughout The Internetworking Area.
✓ All Routers Store All Received Copies Of The Link State Advertisement In A Link State Database.
✓ Each Router Calculates A Shortest Path Tree From The Information In The Topological Database And Enters Routes In Its Routing Tables Based On The Shortest Path Tree.
62. WHY ARE SEQUENCE NUMBERS IMPORTANT IN LINK STATE PROTOCOLS?
Answer: Sequence Numbers Help A Router Differentiate Between Multiple Copies Of The Same Link State Advertisement And Also Prevent Flooded Link State Advertisements From Circulating Endlessly Throughout The Internetwork.
63. WHAT PURPOSE DOES AGING SERVE IN A LINK STATE PROTOCOL?
Answer: Aging Prevents Old, Possibly Obsolete, Link State Information From Residing In A Topological Database Or From Being Accepted By A Router.
64. EXPLAIN HOW AN SPF ALGORITHM WORKS?
Answer:
✓ A Router Builds A Shortest Path Tree By First Adding Itself As The Root. Using The Information In The Topological Database, The Router Creates A List Of All Of Its Directly Connected Neighbors.
✓ The Lowest-cost Link To A Neighbor Becomes A Branch Of The Tree, And That Router's Neighbors Are Added To The List. The List Is Checked For Duplicate Paths, And If They Exist, The Higher-Cost Paths Are Removed From The List.
✓ The Lowest-Cost Router On The List Is Added To The Tree, That Router's Neighbors Are Added To The List, And The List Is Again Checked For Duplicate Paths. This Process Continues Until No Routers Remain On The List.
65. HOW DO AREAS BENEFIT A LINK STATE INTERNETWORK?
Answer: Within A Routing Domain, Areas Are Sub-domains. They Make Link State Routing More Efficient By Limiting The Size Of The Link State Database Of Each Router In The Area.
66. WHAT IS AN AUTONOMOUS SYSTEM?
Answer: Depending On The Usage, An Autonomous System Can Be Defined As An Internetwork Under A Common Administrative Domain Or A Single Routing Domain.
67. WHAT IS THE DIFFERENCE BETWEEN AN INTERIOR GATEWAY PROTOCOL (IGP) AND AN EXTERIOR GATEWAY PROTOCOL (EGP)?
Answer:
✓ An Interior Gateway Protocol Is A Routing Protocol That Routes Within An Autonomous System.
✓ An Exterior Gateway Protocol Is A Routing Protocol That Routes Between Autonomous Systems.
✓ Routing Protocol RIP Was Defined In
• Request For Comments (RFC) 1058
• Internet Standard (STD)
✓ It Uses Distance Vectors To Mathematically Compare Routes To Identify The Best Path To Any Given Destination Address
✓ With The Expansion Of IP Based Networks (More Numerous And Greater In Size)
✓ Update In 1994
✓ RIP2 Defined In 1994 In RFC 1723
✓ The Routing Information Protocol (RIP) Is A Distance-Vector, Interior Gateway (IGP) Routing Protocol Used By Routers To Exchange Routing Information.
✓ RIP Uses The Hop Count As A Routing Metric.
✓ RIP Prevents Routing Loops By Implementing A Limit On The Number Of Hops Allowed In A Path From The Source To A Destination. The Maximum Number Of Hops Allowed For RIP Is 15.
This Hop Limit, However, Also Limits The Size Of Networks That RIP Can Support.RIP Version 2 (RIPv2) Was Developed Due To The Deficiencies Of The Original RIP.
DIFFERENCE BETWEEN RIPv1 Vs RIPv2:
✓ RIPv1 Is Classful Routing Protocol And RIPv2 Classless Routing Protocol.
✓ In RIPv1, Subnet Masks Are NOT Included In The Routing Update And In RIPv2 Subnet Masks Are Included In The Routing Update.
✓ RIPv2 Multicasts The Entire Routing Table To All Adjacent Routers At The Address 224.0.0.9, As Opposed To RIPv1 Which Uses Broadcast (255.255.255.255). Unicast Addressing Is Still Allowed For Special Applications.
BASIC CONFIGURATION:
✓ Cisco IOS, Uses "Router RIP" Command To Enable Rip Routing Protocol. The Version Command Is Used To Specify Which RIP Version To Use (Either 1 Or 2). If The Version Command Is Omitted Then The Router Defaults To Sending RIPv1 But Can Receive Both RIPv1 And RIPv2.
✓ The "Network" Command Is Used To Specify The Directly Connected Subnets On The Router To Be Configured And That Are Intended To Be Included In The Routing Updates.
✓ According To The Classful, Network Specified, The Subnets Of That Network Are Automatically Identified And Participate In The Routing Update. By Default Routing Updates Are Summarized At Network Boundaries.
✓ In RIPv2 This Auto Summarization Behavior Can Be Turned Off Using The "No Auto-Summary" Command. Moreover, Manual Summarization Can Be Configured On A Per Interface Level.
CONFIGURATION EXAMPLE:
R1#Conf T
R1(Config)#Router Rip
R1(Config-Router)#Version 2
R1(Config-Router)#Network 192.168.12.0
R1(Config-Router)#Exit
RIP VERIFICATION:
R1#Show IP Protocol
68. WHAT PORT DOES RIP USE?
Answer: RIP Uses UDP Port 520.
69. WHAT METRIC DOES RIP USE? HOW IS THE METRIC USED TO INDICATE AN UNREACHABLE NETWORK?
Answer: RIP Uses A Hop Count Metric. An Unreachable Network Is Indicated By Setting The Hop Count To 16,Which RIP Interprets As An Infinite Distance.
70. WHAT IS THE UPDATE PERIOD FOR RIP?
Answer: RIP Sends Periodic Updates Every 30 Seconds Minus A Small Random Variable To Prevent The Updates Of Neighboring Routers From Becoming Synchronized.
71. HOW MANY UPDATES MUST BE MISSED BEFORE A ROUTE ENTRY WILL BE MARKED AS UNREACHABLE?
Answer: A Route Entry Is Marked As Unreachable If Six Updates Are Missed.
72. WHAT IS THE PURPOSE OF THE GARBAGE COLLECTION TIMER?
Answer: The Garbage Collection Timer, Or Flush Timer, Is Set When A Route Is Declared Unreachable. When The Timer Expires, The Route Is Flushed From The Route Table. This Process Allows An Unreachable Route To Remain In The Routing Table Long Enough For Neighbors To Be Notified Of Its Status.
73. WHY IS A RANDOM TIMER ASSOCIATED WITH TRIGGERED UPDATES? WHAT IS THE RANGE OF THIS TIMER?
Answer: The Random Timer, Whose Range Is 1 To 5 Seconds, Prevents A "Storm" Of Triggered Updates During A Topology Change.
74. WHAT IS THE DIFFERENCE BETWEEN A RIP REQUEST MESSAGE AND A RIP RESPONSE MESSAGE?
Answer: A Request Message Asks A Router For An Update. A Response Message Is An Update.
75. WHICH TWO TYPES OF REQUEST MESSAGES DOES RIP USE?
Answer: A Request Message May Either Ask For A Full Update Or In Some Special Cases It May Ask For Specific Routes.
76. UNDER WHAT CIRCUMSTANCES WILL A RIP RESPONSE BE SENT?
Answer: A Response Is Sent When The Update Timer Expires, Or Upon Reception Of A Request Message.
77. WHY DOES RIP HIDE SUBNETS AT MAJOR NETWORK BOUNDARIES?
Answer:
✓ RIP Updates Do Not Include The Subnet Mask Of The Destination Address, So A RIP Router Depends On The Subnet Masks Of Its Own Interfaces To Determine How An Attached Major Network Address Is Subnetted.
✓ If A Router Does Not Have An Attachment To A Particular Major Network Address, It Has No Way To Know How That Major Network Is Subnetted. Therefore, No Subnets Of A Major Network Address Can Be Advertised Into Another Major Network.
Interior Gateway Routing Protocol (IGRP) Is A Distance Vector Interior Routing Protocol (IGP) Developed By Cisco. It Is Used By Routers To Exchange Routing Data Within An Autonomous System.
IGRP Is A Proprietary Protocol. IGRP Was Created In Part To Overcome The Limitations Of RIP (Maximum Hop Count Of Only 15, And A Single Routing Metric) When Used Within Large Networks. IGRP Supports Multiple Metrics For Each Route, Including Bandwidth, Delay, Load, MTU, And Reliability; To Compare Two Routes These Metrics Are Combined Together Into A Single Metric, Using A Formula Which Can Be Adjusted Through The Use Of Pre-Set Constants. By Default, The IGRP Composite Metric Is A Sum Of The Segment Delays And The Lowest Segment Bandwidth. The Maximum Hop Count Of IGRP-Routed Packets Is 255 (Default 100), And Routing Updates Are Broadcast Every 90 Seconds (By Default). IGRP Uses Port Number 9 For Communication.
IGRP Is Considered A Classful Routing Protocol. Because The Protocol Has No Field For A Subnet Mask, The Router Assumes That All Subnetwork Addresses Within The Same Class A, Class B, Or Class C Network Have The Same Subnet Mask As The Subnet Mask Configured For The Interfaces In Question. This Contrasts With Classless Routing Protocols That Can Use Variable Length Subnet Masks. Classful Protocols Have Become Less Popular As They Are Wasteful Of IP Address Space.
78. WHICH UDP PORT NUMBER IS USED TO ACCESS IGRP?
Answer: IGRP Does Not Use A UDP Port. It Is Accessed Directly From The Network Layer, As Protocol Number 9.
79. WHAT IS THE MAXIMUM IGRP INTERNETWORK DIAMETER, IN HOPS?
Answer: The Maximum IGRP Network Diameter Is 255 Hops.
80. WHAT IS THE DEFAULT UPDATE PERIOD FOR IGRP?
Answer: The Default IGRP Update Period Is 90 Seconds.
81. WHY DOES IGRP SPECIFY AN AUTONOMOUS SYSTEM NUMBER?
Answer: IGRP Specifies An Autonomous System Number So That Multiple IGRP Processes Can Be Enabled Within The Same Routing Domain And Even On The Same Router.
82. WHAT IS THE DEFAULT IGRP HOLDDOWN TIME?
The Default IGRP Hold Down Time Is 280 Seconds.
83. WHICH VARIABLES CAN IGRP USE TO CALCULATE ITS COMPOSITE METRIC?
Answer: IGRP Can Use Bandwidth, Delay, Load, And Reliability To Calculate Its Metric. By Default, It Uses Only Bandwidth And Delay.
84. HOW MANY ENTRIES CAN BE CARRIED WITHIN A SINGLE IGRP UPDATE PACKET?
Answer: An IGRP Update Packet Can Carry Up To 104 Route Entries.
85. WHICH THREE FIELDS ARE NEW TO THE RIPV2 MESSAGE FORMAT?
Answer: The Route Tag Field, The Subnet Mask Field, And The Next Hop Field Are RIPv2 Extensions That Do Not Exist In RIPv1 Messages. The Basic Format Of The RIP Message Remains Unchanged Between The Two Versions; Version 2 Merely Uses Fields That Are Unused In Version 1.
86. BESIDES THE EXTENSIONS DEFINED BY THE THREE FIELDS OF QUESTION 1, WHAT ARE THE OTHER TWO MAJOR CHANGES FROM RIPV1?
Answer: In Addition To The Functions That Use The New Fields, RIPv2 Supports Authentication And Multicast Updates.
87. WHAT IS THE MULTICAST ADDRESS USED BY RIPV2? WHAT IS THE ADVANTAGE OF MULTICASTING MESSAGES OVER BROADCASTING THEM?
Answer: RIPv2 Uses The Multicast Address 224.0.0.9. Multicasting Of Routing Messages Is Better Than Broadcasting Because Hosts And Non-Ripv2 Routers Will Ignore The Multicast Messages.
88. WHAT IS THE PURPOSE OF THE ROUTE TAG FIELD IN THE RIPV2 MESSAGE?
Answer: When Another Routing Protocol Uses The Ripv2 Domain As A Transit Domain, The Protocol External To RIPv2 Can Use The Route Tag Field To Communicate Information To Its Peers On The Other Side Of The RIPv2 Domain.
89. WHAT IS THE PURPOSE OF THE NEXT HOP FIELD?
Answer: The Next Hop Field Is Used To Inform Other Routers Of A Next-Hop Address On The Same Multi Access Network That Is Metrically Closer To The Destination Than The Originating Router.
90. WHAT IS THE UDP PORT NUMBER USED BY RIPV2?
Answer: RIPV2 Uses The Same UDP Port Number As RIPv1, Port Number 520.
91. WHICH ONE FEATURE MUST A ROUTING PROTOCOL HAVE TO BE A CLASSLESS ROUTING PROTOCOL?
Answer: A Classless Routing Protocol Does Not Consider The Major Network Address In Its Route Lookups, But Just Looks For The Longest Match.
92. WHICH ONE FEATURE MUST A ROUTING PROTOCOL HAVE TO USE VLSM?
Answer: To Support VLSM, A Routing Protocol Must Be Able To Include The Subnet Mask Of Each Destination Address In Its Updates.
93. WHICH TWO TYPES OF AUTHENTICATION ARE AVAILABLE WITH CISCO'S RIPV2? ARE THEY BOTH DEFINED IN RFC 1723?
Answer: Cisco's Implementation Of RIPv2 Supports Clear-Text Authentication And MD5 Authentication. Only Clear-Text Authentication Is Defined In RFC 1723.
Enhanced Interior Gateway Routing Protocol (EIGRP) Is A Distance Vector Protocol That Uses The Same Sophisticated Metric As IGRP And Uses The Diffusing Update Algorithm (DUAL) Convergence Algorithm. EIGRP Is Able To Converge Quickly And Use Little Bandwidth Because It—Like OSPF—Has Separate Keepalives And Reliable Updates. EIGRP Is Sometimes Referred To As A Hybrid Routing Protocol, Although Advanced Distance Vector Routing Protocol Is Probably A More Accurate Description.
EIGRP Is An Efficient But Proprietary Solution For Large Networks. Its Ability To Scale Is Limited Only By The Design Of The Network.
EIGRP Features And Advantages: The Goal Of EIGRP Is To Solve The Scaling Limitations That IGRP Faces, While Keeping The Advantages Of Distance Vector Routing Protocols: Simplicity, Economy Of Memory, And Economy Of Processor Resources. EIGRP Is Scalable In Terms Of Hardware Resources And Network Capacity. EIGRP Is Also Lightning Fast.
CISCO IDENTIFIES FOUR PRINCIPAL COMPONENTS OF EIGRP:
Protocol-Dependent Modules — EIGRP Supports Several Routed Protocols Independently. The Two That Are Of Interest Today Are Ip And IPv6.
Reliable Transport Protocol —EIGRP Sends Some Packets Reliably Using A Reliable Transport Protocol.
Neighbor Discovery And Recovery — EIGRP Uses Hellos To Identify Its Neighbors Quickly And To Recognize When Those Neighbors Are Down.
Diffusing Update Algorithm (DUAL)— DUAL Identifies The Procedure Used To Sort The List Of Available Paths And Select Best Paths And Feasible Fail-Over Routes.
EIGRP HAS THE FOLLOWING CHARACTERISTICS:
✓ Distance-Vector Protocol That Uses Some Link-State Features
✓ Event Triggered Updates
✓ Fast Convergence
✓ Cisco Proprietary
✓ Easy To Configure
✓ Automatic Redistribution Into IGRP
94. IS EIGRP A DISTANCE VECTOR OR A LINK STATE ROUTING PROTOCOL?
Answer: EIGRP Is A Distance Vector Protocol.
95. WHAT IS THE MAXIMUM CONFIGURED BANDWIDTH EIGRP WILL USE ON A LINK? CAN THIS PERCENTAGE BE CHANGED?
Answer: By Default, EIGRP Uses No More Than 50% Of The Link's Bandwidth, Based On The Bandwidth Configured On The Router's Interface. This Percentage To Be Changed With The Command IP Bandwidth-Percent EIGRP.
96. HOW DO EIGRP AND IGRP DIFFER IN THE WAY THEY CALCULATE THE COMPOSITE METRIC?
Answer: EIGRP And IGRP Use The Same Formula To Calculate Their Composite Metrics, But EIGRP Scales The Metric By A Factor Of 256.
97. WHAT ARE THE FOUR BASIC COMPONENTS OF EIGRP?
Answer:
The Four Basic Components Of EIGRP Are:
✓ The Protocol Dependent Modules
✓ The Reliable Transport Protocol
✓ The Neighbor Discovery And Recovery Module
✓ The Diffusing Update Algorithm
98. IN THE CONTEXT OF EIGRP, WHAT DOES THE TERM RELIABLE DELIVERY MEAN? WHICH TWO METHODS ENSURE RELIABLE DELIVERY OF EIGRP PACKETS?
Answer: Reliable Delivery Means EIGRP Packets Are Guaranteed To Be Delivered, And They Are Delivered In Order. RTP Uses A Reliable Multicast, In Which Received Packets Are Acknowledged, To Guarantee Delivery; Sequence Numbers Are Used To Ensure That They Are Delivered In Order.
99. WHICH MECHANISM ENSURES THAT A ROUTER IS ACCEPTING THE MOST RECENT ROUTE ENTRY?
Answer: Sequence Numbers Ensure That A Router Is Receiving The Most Recent Route Entry.
100. WHAT IS THE MULTICAST IP ADDRESS USED BY EIGRP?
Answer: EIGRP Uses The Multicast Address 224.0.0.10.
101. WHAT ARE THE PACKET TYPES USED BY EIGRP?
Answer:
The Packet Types Used By EIGRP Are:
✓ Hellos
✓ Acknowledgments
✓ Updates
✓ Queries
✓ Replies
102. AT WHAT INTERVAL, BY DEFAULT, ARE EIGRP HELLO PACKETS SENT?
Answer: By Default EIGRP Hello Interval Is 5 Seconds, Except On Some Slow-Speed (T1 And Below) Interfaces, Where The Default Is 60 Seconds.
103. WHAT IS THE DEFAULT HOLD TIME?
Answer: The EIGRP Default Hold Time Is Three Times The Hello Interval.
104. WHAT IS THE DIFFERENCE BETWEEN THE NEIGHBOR TABLE AND THE TOPOLOGY TABLE?
Answer: The Neighbor Table Stores Information About EIGRP-Speaking Neighbors.
The Topology Table Lists All Known Routes That Have Feasible Successors.
105. WHAT IS A FEASIBLE DISTANCE?
Answer: The Feasible Distance To A Destination Is A Router's Lowest Calculated Distance To The Destination.
106. WHAT IS THE FEASIBILITY CONDITION?
Answer: The Feasibility Condition Is The Rule By Which Feasible Successors Are Chosen For A Destination. The Feasibility Condition Is Satisfied If A Neighbor's Advertised Distance To A Destination Is Lower Than The Receiving Router's Feasible Distance To The Destination. In Other Words, A Router's Neighbor Meets The Feasibility Condition If The Neighbor Is Metrically Closer To The Destination Than The Router.
Another Way To Describe This Is That The Neighbor Is "Downstream" Relative To The Destination.
107. WHAT IS A FEASIBLE SUCCESSOR?
Answer: A Feasible Successor To A Destination Is A Neighbor That Satisfies The Feasibility Condition For That Destination.
108. WHAT IS A SUCCESSOR?
Answer: A Successor To A Destination Is A Feasible Successor That Is Currently Being Used As The Next Hop To The Destination.
109. WHAT IS THE DIFFERENCE BETWEEN AN ACTIVE ROUTE AND A PASSIVE ROUTE?
Answer: A Route Is Active On A Particular Router If The Router Has Queried Its Neighbors For A Feasible Successor And Has Not Yet Received A Reply From Every Queried Neighbor.
Answer: The Route Is Passive When There Are No Outstanding Queries.
110. WHAT CAUSES A PASSIVE ROUTE TO BECOME ACTIVE?
Answer: A Route Becomes Active When No Feasible Successor Exists In Its Topology Table.
111. WHAT CAUSES AN ACTIVE ROUTE TO BECOME PASSIVE?
Answer: An Active Route Becomes Passive When A Reply Has Been Received From Every Queried Neighbor.
112. WHAT DOES STUCK-IN-ACTIVE MEAN?
Answer: If A Router Does Not Receive A Reply From A Queried Neighbor Within The Active Time (3 Minutes, By Default), The Route Is Declared Stuck-In-Active.
A Response With An Infinite Metric Is Entered On The Neighbor's Behalf To Satisfy DUAL, And The Neighbor Is Deleted From The Neighbor Table.
113. WHAT IS THE DIFFERENCE BETWEEN SUBNETTING AND ADDRESS AGGREGATION?
Answer: Subnetting Is The Practice Of Creating A Group Of Subnet Addresses From A Single IP Network Address.
Address Aggregation Is The Practice Of Summarizing A Group Of Network Or Subnet Addresses With A Single IP Network Address.
The Open Short Path First (OSPF) Is Defined In RFC 2328.It Is An Interior Gateway Protocol Used To Distribute Routing Information Within A Single Autonomous System. It Is A Most Common Routing Protocol Using By Service Providers, Because Unlike EIGRP It Is An Open Standard Protocol.
Why We Are Calling OSPF Is A Link State Routing Protocol. Unlike RIP, OSPF Is Not Only Sending The Routing Updates To Its Neighbors. It Is Sending All The Information About The Link Like IP Address Of The Interface And Subnet Mask, The Type Of Network It Is Connected To (P2P Or P2Multi-Point Or FR) And The Routers Which Is Connected To It. The Collection Of These Link States Will Form A Link State Database.
OSPF Vs RIP: Comparison between RIP Vs OSPF is given below.
RIP:
◙ - ➤ RIP Has Limited HOP Counts. It Is 16.A RIP Network Spans More Than 15 HOPS, Considered As Unreachable.
◙ - ➤ RIP Doesn’t Support For VLSM.
◙ - ➤ Periodic Update Of Routing Table Consumes Lots Of Bandwidth Especially On WAN Clouds.
◙ - ➤ RIP Converges Slower Than OSPF Does.
◙ - ➤ RIP Network Is A FLAT Network. Here No Concept Of Areas & Boundaries & Summarization.
OSPF
◙-◙ No Limitations On The Hop Count.
◙-◙ Can Use VLSM
◙-◙ Converges Quickly
◙-◙ Can Divide Into Areas. This Will Help Us To Use Summarization.
◙-◙ Allows Authentication.
◙-◙ It Uses Dijkstra’s Algorithm (SPF Algorithm) Reducing The Usage Of BW, By Sending Triggered Updates To Announce The Network Changes.
◙-◙ Sending Periodic Updates On Long Intervals (30 Mins).
Unlike RIP, OSPF Doesn’t Send Any Routing Updates On Periodic Intervals. It Will Only Send Triggered Updates. It Means Every Time It Doesn’t Send Full Routing Table To Its Neighbors. Whenever Any Changes In Network, Like New Router Added Or A Router Removed From The Network, It Will Send Information About That Particular Network To Its Neighbor.
TYPES OF TABLES USED IN OSPF.
1. Neighbor Table
2. Topology Table
3. Routing Table
◙ - ➤ NEIGHBOR TABLE: The Router Tracks All The Neighbors Which Is Running OSPF As A Routing Protocol And Put That Information In This Table. It Contains All The Information About The Directly Connected Neighbors. Like Their Router Id, To Which Network They Are Connected, And Which Network They Are Advertising. It Will Exchange Routing Information With Routers Which Is In This Table.
◙ - ➤ TOPOLOGY TABLE: This Is The One Of The Big Difference Between Distance Vector And Link-State Protocols. Distance Vector Protocol Doesn’t Have This Topology Table. They Only Know About The Directly Connected Neighbors. This Table Is A Road Map For Each And Every Single Network Which Is Available In A Particular Area. All The Routers In A Particular Area Will Be Having The Same Type Of Topology Table.
◙ - ➤ ROUTING TABLE: This Table Contains All The Best Routes To Reach A Particular Network. Based On The Topology Table It Will Be Having Multiple Paths For A Single Destination Network. It Will Run The Spf Algorithm To Find The Best Routes For Each And Every Network.
The Algorithm Places Each Router At The Root Of A Tree And Calculates The Shortest Path To Each Destination Based On The Cumulative Cost Required To Reach That Destination. Each Router Will Have Its Own View Of The Topology Even Though All The Routers Will Build A Shortest Path Tree Using The Same Link-State Database.
HOW TO CALCULATE OSPF COST? Interface Cost Is Derived From The Bandwidth. Formula Is:
OSPF’S COST= 10000 0000/Bandwith In BPS
Cost = Reference / Bandwidth.
By default, Reference is 100000 [ Kb/s ].
So, For Your Bandwidth Of 5120, Cost Should Be:
Cost = 100000 / 5120 = 19.53. Rounded Down To The Closest Integer, It's 19.
If You Want To Have Cost Of 51, You Would Need To Recalculate Your Bandwidth:
51 = 100000 / x => x= 100000 / 51 = 1960.78. Round it down to 1960.
THE CHARACTERISTICS OF OSPF AREA: Areas Are Similar To Subnets In That Routes & Networks Which Can Be Summarized Easily.
◙-◙ OSPF Divides The Network Into Multiple Areas.
◙-◙ Each Area Can Contain N Number Of Routers.
◙-◙ All The Areas Should Connect To Area 0(Backbone Area)
◙-◙ All The Routers Within The Same Area Will Be Having The Same Topology Table
◙-◙ It Contains One Autonomous System Border System ROUTER(ASBR)
◙-◙ While Creating Multiple Areas In OSPF, We Should Create Area 0 (Backbone Area) First And Then Only We Should Create Other Areas. But All The Areas Should Connect To Area 0.
◙-◙ The Routers Which Will Be Having Only One SPF Link Database Are Called Internal Router (IR).
◙-◙ The Routers Those Which Have Interfaces In Multiple Areas Are Called Area Border Router (ABR).
◙-◙ A Router Which Connects, OSPF With Other Routing Protocol Is Called As Autonomous System Border Router (ASBR).
◙-◙ A Router Which Is Only In Area 0 Or Backbone Area Is Known As Backbone Area Router.
TYPES OF AREAS: There Are Five Types Of Areas Are There In OSPF, Which Is Listed Below:
◙ Normal Area
◙ Stub Area
◙ Totally Stub Area
◙ No So Stubby Area
◙ Backbone Area
WHY WE ARE DIVIDING NETWORKS INTO MULTIPLE AREAS?
◙ The Goal Is To Localize Routing Updates Within The Same Area.
◙ It Requires A Hierarchical Design In IP Address Allocation.
◙ ABR & ASBR Are The Only Two Router Types Where We Can Do Summarization.
Let’s Consider We Are Running A Company With 100 Routers. We Are Using OSPF As An Internal Routing Protocol. All The Routers Which Are Running OSPF Will Be Having Same Topology Of The Entire Network. If Any Link Goes Down At Any Point Of Network, All The Routers Will Come To Know About That Link Failure. Then All The Routers Will Run SPF Algorithm To Find An Alternative Path To Reach The Other Networks. It Will Take More Time To Converge And To Calculate An Alternative Path If The Network Is Large. The Purpose Of Area Is To Minimize This.
If We SPLIT Those 100 Routers Into 2 Areas, Say Area 1 & Area 2 And Each Area Contains 50 Routers. And Both The Areas Are Connected To Area 0.In This Scenario Area 1 Doesn’t Care Any Change Happens In Area 2.If Any Link In Area 2 Goes Down That Will Be Localized Within Area 2.Only Those Which Are In Area 2 Need To Run SPF To Find The Alternative Path. Area 1 Doesn’t Care, Even Doesn’t Know About That Link Failure, Which Occurs In Area 2. So The OSPF Converges Quickly. It Is More Processor Efficient.
OSPF NEIGHBOR RELATIONSHIPS: Routers That Share A Common Segment Become Neighbors On That Segment. Neighbors Are Elected Via The Hello Protocol. Hello Packets Are Sent Periodically Out Of Each Interface Using IP Multicast. Routers Become Neighbors As Soon As They See Themselves Listed In The Neighbor's Hello Packet.
TWO ROUTERS WILL NOT BECOME NEIGHBORS UNLESS THEY AGREE ON THE FOLLOWING:
◙ They Need To Be In Same Area.
◙ They Need To Have Same Mask.
◙ Hello And Dead Timers Should Be Same On Both The Routers.
◙ Password Should Be Same On Both The Routers, If Authentication Is Enabled.
◙ - ► OSPF PACKET TYPES:
✓ HELLO –➤ Discovers Neighbors And Builds Adjacencies Between Them
✓ DATABASE DESCRIPTION (DBD) –➤ Checks For Db Synchronization Between Routers By Sending A Summary List Of All Routes In DB
✓ LINKS STATE REQUEST (LSR) –➤ Requests Specific Link State Records From Another Router
✓ LINK STATE UPDATE (LSU) –➤ Sends Specifically Requested Link State Requests
✓ LINK STATE ACKNOWLEDGEMENT (LSACK) –➤ Acknowledges The Other Packet Types
TO DISCOVER THE NEIGHBOR, OSPF WILL SEND HELLO PACKETS VIA THE OSPF ENABLED INTERFACE. THIS HELLO PACKET CONTAINS THE FOLLOWING INFORMATION.
◙ Router ID
◙ Hello And Dead Timers
◙ Network Mask
◙ Area ID
◙ Router Priority
◙ DR & BDR IP Address
ROUTER ID:
◙ The Router Id Is Nothing But The Router’s Name In The Ospf Process.
◙ Highest Active Interface Will Become Router ID.
◙ Loopback Beats Physical Interface.
HELLO AND DEAD TIMERS:
◙ OSPF Exchanges Hello Packets On Each Segment. This Is A Form Of Keepalive Used By Routers To Acknowledge Their Existence On A Segment.
◙ The Dead Interval Is The Number Of Seconds That A Router's Hello Packets Have Not Been Received Before Its Neighbors Consider To Be Down.
◙ Hello Packets Are Sent Once In Every 10 Secs On Broadcast/Point To Point Network & 30 Secs On Non Broadcast Multi-Access.
OSPF ADJACENCIES: The Adjacency Building Process Takes Effect After Multiple Stages Have Been Fulfilled. Routers That Become Adjacent Will Have The Exact Link-State Database. The Following Is A Brief Summary Of The States An Interface Passes Through Before Becoming Adjacent To Another Router:
DOWN: Hello Packets Have Been Sent The Router Is Waiting To Hear The Response From The Routers To Which It Sent Hello Packets.
ATTEMPT: This State Indicates That No Recent Information Has Been Received From The Neighbor. An Effort Should Be Made To Contact The Neighbor By Sending Hello Packets At The Reduced Rate Poll Interval.
INIT: The Interface Has Detected A Hello Packet Coming From A Neighbor But Bi-Directional Communication Has Not Yet Been Established. It Means The Router Needs To Acknowledge.
TWO-WAY: There Is Bi-Directional Communication With A Neighbor. The Router Has Seen Its Router Id In The Hello Packets Coming From A Neighbor. With This Info The Router Will Know That Whether It Is A New Neighbor Or Reply From An Old Neighbor.
At The End Of This Stage The Dr And BDR Election Would Be Done. At The End Of The 2way Stage, Routers Will Decide Whether We Can Build An Adjacency Or Not. The Decision Is Based On DR& BDR And The Type Of Network With Which Is Connected To.
EXSTART: Now Routers Are Trying To Establish The Initial Sequence Number That Is Going To Be Used In The Information Exchange Packets. The Sequence Number Is Used To Get The Most Recent Information.
EXCHANGE: Routers Will Send Their Whole Link-State Database By Sending Database Description Packets (DBD).In This Stage Router Won’t Send Its Entire Database To Its Neighbors. It Will Send Only Notes Of The Routing Table.
LOADING: At This State, Routers Have Built A Link-State Request List And A Link-State Retransmission List. Based On The DBD, If Any Information That Looks Incomplete Will Be Put On The Request List. Any Update That Is Sent Will Be Put On The Retransmission List Until It Gets Acknowledged.
FULL: At This State, The Adjacency Is Complete. The Neighboring Routers Are Fully Adjacent. Adjacent Routers Will Have A Similar Link-State Database.
After Sharing The Link-State Database The OSPF Will Start To Calculate The Best Path For Each And Every Network. This Is The Time To Run The SPF Algorithm. Once It Finds The Best Path To Each And Every Network, It Will Put Those Routes Into Its Routing Table. Till The Link Which Is In Routing Table Goes Down, OSPF Will Never Run SPF.
ADJACENCY BEHAVIOR IN POINT-TO-POINT LINKS:
◙ OSPF Packets Sent Using A Destination Address Of 224.0.0.5
ADJACENCY BEHAVIOR IN BROADCAST MULTIACCESS NETWORKS:
◙ DR And BDR Selection Are Required
◙ All Neighbor Routers Form Adjacencies With DR And BDR Only
◙ Packets To The DR And BDR Are Addressed To 224.0.0.6
◙ Packets From DR To All Other Routers Is 224.0.0.5
OSPF OVER FRAME-RELAY – FIVE MODES OF OSPF OPERATION ARE AVAILABLE
BROADCAST – CISCO EXTENSION:
◙ Has One IP Subnet
◙ Uses Multicast OSPF Hello Packets To Discover Neighbors
◙ Elects Dr And BDR
◙ Requires A Full-Mesh Or Partial-Mesh Topology
NONBROADCAST (NBMA) – RFC 2328
◙ Has One IP Subnet
◙ Requires Neighbors To Be Manually Configured
◙ Elects Dr And BDR
◙ Requires That The DR And BR Have Full Connectivity With All Other Routers
◙ Typically Used In A Full-Mesh Or Partial-Mesh Topology
POINT-TO-MULTIPOINT – RFC 2328
◙ Has One IP Subnet
◙ Uses Multicast OSPF Hello Packets To Discover Neighbors
◙ Does Not Require Dr And BDR
◙ Typically Used In A Partial-Mesh Or Star Topology
POINT-TO-MULTIPOINT NONBROADCAST – CISCO EXTENSION
◙ Used In Place Of RFC Compliant Point-To-Multipoint If Multicast And Broadcast Are Not Enabled On The Virtual Circuit
◙ Requires Neighbors To Be Manually Configured
◙ Does Not Require Dr And BDR
POINT-TO-POINT – CISCO EXTENSION:
◙ Unique Subnet On Each Subinterface
◙ Does Not Have DR And BDR
◙ Used When Only Two Routers Need To Form An Adjacency On A Pair Of Interfaces
◙ Can Be Used With Either Lan Or Wan Interfaces
LSA TYPES:
◙ Type 1 – Router LSAS: – Generated By Every Router In An Area And Does Not Cross An ABR
◙ Type 2 – Network LSAS: – Advertised By Dr And Does Not Cross An ABR
◙ Type 3 – Summary LSAS: – Advertised By The ABR Of The Originating Area
◙ Type 4 – Summary LSAS: – Used To Advertise A Metric To The ASBR And Advertised By The ABR Of The Originating Area
◙ Type 5 – As External LSAS: – Used To Advertise Network From Other Autonomous Systems And Is Advertised And Owned By The Originating ASBR (Need Type 4 To Find The ASBR)
◙ Type 6: – Multicast OSPF LSAS
◙ Type 7 – LSAS Defined For Not-So-Stubby Areas (NSSA): – Used To Advertise Networks From Other Autonomous Systems Injected Into An NSSA Area And Is Advertised And Owned By The Originating ASBR. Translated To Type 5 By The NSSA ABR
◙ Type 8 – External Attribute LSAS For BGP
◙ Types 9, 10 & 11: – Opaque LSAS
TYPES OF OSPF ROUTES
◙ OSPF Intra-Area Routes (Router LSA And Network LSA)
✓ IA – OSPF Interarea Routes (Summary LSA) ✓ E1 – OSPF Type 1 External Routes (Advertised By External LSA)
◙ E2 – OSPF Type 2 External Routes (Advertised By External LSA) – This Is The Default For Redistributed Routes
◙ E1 – External Routes Calculate The Cost By Adding The External Cost To The Internal Cost Of Each Link That The Packet Crosses
◙ E2 – The External Cost Of O E2 Packets Routes Is Always The External Cost Only
OSPF PASSIVE INTERFACE
◙ The Sending And Receiving Of Routing Updates Is Disabled
◙ The Specified Interface Address Appears As A Stub Network In The OSPF Domain
DESIGN LIMITATIONS OF OSPF:
◙ If More Than One Area Is Configured, One Must Be Area 0, The Backbone Area
◙ All Areas Must Be Connected To Area 0
◙ Area 0 Must Be Contiguous
VIRTUAL LINKS
◙ An Extension Of The Backbone
◙ Carried By Nonbackbone Area
◙ Cannot Be Created Across A Stub Or NSSA Area
◙ Used To Allow Areas To Connect To Areas Other Than Area 0
◙ Used To Repair A Discontiguous Area 0
AREA TYPES:
◙ Backbone Area – Connects All Other Areas
◙ Normal Area – Contains All Internal And External Routing Information
◙ Stub Area – Contains Internal And Area Routing Information, But Not External Routing Information
◙ Totally Stubby Area – Contains Area Routing Information Only. Cisco Proprietary
◙ NSSA – Contains Area And External Routing Information
OSPF AUTHENTICATION:
◙ Simple Password Authentication
◙ MD5 Authentication
◙ Router Generates And Checks Every OSPF Packet
◙ The Source Of Each Routing Update Packet Received Is Authenticated
◙ Each Participating Neighbor Must Have The Same Key (Password) Configured.
FOR OSPF MORE REFERENCE:
1. ◙ - ➤ OSPF Vs EIGRP, BGP And RIP:
2. ◙ - ➤ OSPF Short Notes:
3. ◙ - ➤ Just Recap About OSPF:
4. ◙ - ➤ OSPF Quick Reference:
5. ◙ - ➤ OSPF Quick Reference Table:
6. ◙ - ➤ OSPFv2 (IPv4) Vs OSPFv3 (IPv6):
7. ◙ - ➤ OSPF Review Questions And Answers:
8. ◙ - ➤ OSPF LSA Types And LSA Operation:
9. ◙ - ➤ OSPF Configuration Examples:
10. ◙ - ➤ OSPF MD5 Authentication:
11. ◙ - ➤ Redistribution OSPF With BGP And EIGR:
114. WHAT IS AN OSPF NEIGHBOR?
Answer: From The Perspective Of An OSPF Router, A Neighbor Is Another OSPF Router That Is Attached To One Of The First Router's Directly Connected Links.
115. WHAT IS AN OSPF ADJACENCY?
Answer: An OSPF Adjacency Is A Conceptual Link To A Neighbor Over Which LSAs Can Be Sent.
116. WHAT ARE THE FIVE OSPF PACKET TYPES? WHAT IS THE PURPOSE OF EACH TYPE?
Answer:
OSPF Packet Types, As OSPF Link-State Information Is Shared Between Areas, An Intricate Set Of Mechanisms Is Followed, Relying On A Number Of Different OSPF Packet Types. All OSPF Traffic Is Transmitted Inside IP Packets. Receivers Recognize OSPF Traffic Because It Is Marked As IP Protocol 89.
OSPF PACKET TYPES AND THEIR PURPOSES:
✓ Hello packets — Establish Communication With Directly Attached Neighbors.
✓ Database Descriptor (DBD) — Sends A List Of Router Ids From Whom The Router Has An LSA And The Current Sequence Number. This Information Is Used To Compare Information About The Network.
✓ Link State Requests (LSR) — Follow DBDs To Ask For Any Missing LSAs.
✓ Link State Update (LSU) — Replies To A Link-State Request With The Requested Data.
✓ Link-State Acknowledgements (LSACK) — Confirm Receipt Of Link-State Information.
117: WHAT IS AN LSA? HOW DOES AN LSA DIFFER FROM AN OSPF UPDATE PACKET?
Answer: A Router Originates A Link State Advertisement To Describe One Or More Destinations.
An OSPF Update Packet Transports LSAs From One Neighbor To Another. Although LSAs Are Flooded Throughout An Area Or OSPF Domain, Update Packets Never Leave A Data Link.
118. WHAT ARE LSA TYPES 1 TO 5 AND LSA TYPE 7? WHAT IS THE PURPOSE OF EACH TYPE?
Answer:
THE MOST COMMON LSA TYPES AND THEIR PURPOSES ARE:
✓ Type 1 (Router LSAs) Are Originated By Every Router And Describe The Originating Router, The Router's Directly Connected Links And Their States, And The Router \ XD5 S Neighbors.
✓ Type 2 (Network LSAs) Are Originated By Designated Routers On Multiaccess Links And Describe The Link And All Attached Neighbors.
✓ Type 3 (Network Summary LSAs) Are Originated By Area Border Routers And Describe Inter-Area Destinations.
✓ Type 4 LSAs (ASBR Summary LSAs) Are Originated By Area Border Routers To Describe Autonomous System Boundary Routers Outside The Area.
✓ Type 5 (AS External LSAs) Are Originated By Autonomous System Boundary Routers To Describe Destinations External To The OSPF Domain.
✓ Type 7 (NSSA External LSAs) Are Originated By Autonomous System Boundary Routers Within Not-So-Stubby Areas.
119. WHAT IS A LINK STATE DATABASE? WHAT IS LINK STATE DATABASE SYNCHRONIZATION?
Answer:
The Link State Database Is Where A Router Stores All The OSPF LSAs It Knows Of, Including Its Own.
Database Synchronization Is The Process Of Ensuring That All Routers Within An Area Have Identical Link State Databases.
120. WHAT IS THE DEFAULT HELLO INTERVAL?
Answer: The Default OSPF Hello Interval Is 10 Seconds.
121. WHAT IS THE DEFAULT ROUTER DEAD INTERVAL?
Answer: The Default Router Dead Interval Is Four Times The Hello Interval.
122. WHAT IS A ROUTER ID? HOW IS A ROUTER ID DETERMINED?
Answer: A Router ID Is An Address By Which An OSPF Router Identifies Itself. It Is Either The Numerically Highest IP Address Of All The Router's Loopback Interfaces, Or If No Loopback Interfaces Are Configured, It Is The Numerically Highest IP Address Of All The Router's LAN Interfaces.
123. WHAT IS AN AREA?
Answer: An Area Is An OSPF Sub-Domain, Within Which All Routers Have An Identical Link State Database.
124. WHAT IS THE SIGNIFICANCE OF AREA 0?
Answer: Area 0 Is The Backbone Area. All Other Areas Must Send Their Inter-Area Traffic Through The Backbone.
125. WHAT IS MAXAGE?
Answer: Maxage, 1 Hour, Is The Age At Which An LSA Is Considered To Be Obsolete.
126. WHAT ARE THE FOUR OSPF ROUTER TYPES?
Answer:
◙ - ➤ Internal Routers, Whose OSPF Interfaces All Belong To The Same Area
◙ - ➤ Backbone Routers, Which Are Internal Routers In Area 0 Area
◙ - ➤ Border Routers, Which Have OSPF Interfaces In More Than One Area Autonomous System Boundary Routers, Which Advertise External Routes Into The OSPF Domain.
127. WHAT ARE THE FOUR OSPF PATH TYPES?
Answer:
✓ Intra-Area Paths
✓ Inter-Area Paths
✓ Type 1 External Paths
✓ Type 2 External Paths
128. WHAT ARE THE FIVE OSPF NETWORK TYPES?
Answer:
✓ Point-To-Point Networks
✓ Broadcast Networks
✓ Non-Broadcast Multi-Access (NBMA) Networks
✓ Point-To-Multipoint Networks
✓ Virtual Links
129. WHAT IS A DESIGNATED ROUTER?
Answer: A Designated Router Is A Router That Represents A Multiaccess Network, And The Routers Connected To The Network, To The Rest Of The OSFP Domain.
130. HOW DOES A CISCO ROUTER CALCULATE THE OUTGOING COST OF AN INTERFACE?
Answer: Cisco IOS Calculates The Outgoing Cost Of An Interface As 108/BW, Where BW Is The Configured Bandwidth Of The Interface.
131. WHAT IS A PARTITIONED AREA?
Answer: An Area Is Partitioned If One Or More Of Its Routers Cannot Send A Packet To The Area's Other Routers Without Sending The Packet Out Of The Area.
132. WHAT IS A VIRTUAL LINK?
Answer: A Virtual Link Is A Tunnel That Extends An OSPF Backbone Connection Through A Non-Backbone Area.
133. WHAT IS THE DIFFERENCE BETWEEN A STUB AREA, A TOTALLY STUBBY AREA, AND A NOT-SO-STUBBY AREA?
Answer:
✓ A Stub Area Is An Area Into Which No Type 5 LSAs Are Flooded.
✓ A Totally Stubby Area Is An Area Into Which No Type 3, 4, Or 5 LSAs Are Flooded, With The Exception Of Type 3 Lsas To Advertise A Default Route.
✓ Not-So-Stubby Areas Are Areas Through Which External Destinations Are Advertised Into The OSPF Domain, But Into Which No Type 5 Lsas Are Sent By The ABR.
134. WHAT IS THE DIFFERENCE BETWEEN OSPF NETWORK ENTRIES AND OSPF ROUTER ENTRIES?
Answer: OSPF Network Entries Are Entries In The Route Table, Describing IP Destinations. OSPF Router Entries Are Entries In A Separate Route Table That Record Only Routes To ABRs And ASBRs.
135. WHY IS TYPE 2 AUTHENTICATION PREFERABLE OVER TYPE 1 AUTHENTICATION?
Answer: Type 2 Authentication Uses MD5 Encryption, Where As Type 1 Authentication Uses Clear-Text Passwords.
136. WHICH THREE FIELDS IN THE LSA HEADER DISTINGUISH DIFFERENT LSAS? WHICH THREE FIELDS IN THE LSA HEADER DISTINGUISH DIFFERENT INSTANCES OF THE SAME LSA?
Answer: The Three Fields In The LSA Header That Distinguish Different LSAs Are The Type, Advertising Router, And The Link State ID Fields. The Three Fields In The LSA Header That Distinguish Different Instances Of The Same LSA Are The Sequence Number, Age, And Checksum Fields.
FOR BGP REFERENCES:
1 ◙ - ➤ BGP Quick References:
2 ◙ - ➤ BGP Neighbors Concepts:
3 ◙ - ➤ BGP Lab Virtual Link:
4 ◙ - ➤ BGP Lab For Route Reflectors Client:
5 ◙ - ➤ BGP Lab Redistribute Versus OSPF:
6 ◙ - ➤ Redistribution BGP Vs OSPF And EIGRP:
7 ◙ - ➤ BGP MD5 Authentication:
8. ◙ - ➤ just Recap References About BGP With Questions And Answers:
Intermediate System to Intermediate System (IS-IS) Is Defined By ISO/IEC 10589 And Was Initially Developed By The International Organization For Standardization (ISO) In 1992. This Development Was At The Same Time That The Internet Architecture Board Was Developing Open Shortest Path First (OSPF), Defined By The Internet Engineering Task Force (IETF) In RFC 1131. IS-IS Was Initially Developed To Support The OSI Layer 3 Routing Protocol Connectionless Mode Network Service (CLNS). Integrated IS-IS Was Developed As An Extension To The Original IS-IS Specification To Support IP Routing.
IS-IS Is A Routing Protocol Designed To Move Information Efficiently Within A Computer Network, A Group Of Physically Connected Computers Or Similar Devices. It Accomplishes This By Determining The Best Route For Datagrams Through A Packet-Switched Network. The Protocol Was Defined In ISO/IEC 10589:2002 As An International Standard Within The Open Systems Interconnection (OSI) Reference Design. Though Originally An ISO Standard, The IETF Republished The Protocol As An Internet Standard In RFC 1142 . IS-IS Has Been Called "The De Facto Standard For Large Service Provider Network Backbones
137. WHAT IS AN INTERMEDIATE SYSTEM?
Answer: An Intermediate System Is The ISO Term For A Router.
138. WHAT IS A NETWORK PROTOCOL DATA UNIT?
Answer: A Network Protocol Data Unit Is The ISO Term For A Packet.
139. WHAT IS THE DIFFERENCE BETWEEN AN L1, AN L2, AND AN L1/L2 ROUTER?
Answer:
✓ An L1 Router Has No Direct Connections To Another Area. An L2 Router Only Routes Inter-Area Traffic.
✓ An L1/L2 Router Routes Both Inter-Area And Intra-Area Traffic And Acts As An Inter-Area Gateway For L1 Routers.
140. EXPLAIN THE BASIC DIFFERENCE BETWEEN AN IS-IS AREA AND AN OSPF AREA.
Answer: The Borders Of IS-IS Areas Are Between Routers, On Links. The Borders Of OSPF Areas Are Defined By The Routers Themselves.
141. WHAT IS A NETWORK ENTITY TITLE (NET)?
Answer: The Network Entity Title Is An Address By Which A Router Identifies Both Itself And The Area In Which It Resides.
142. TO WHAT VALUE MUST THE NSAP SELECTOR BE SET IN A NET?
Answer: The NSAP Selector Should Be Set To 0x00 In A NET.
143. WHAT IS THE PURPOSE OF A SYSTEM ID?
Answer: The System ID Uniquely Identifies A Router Within An IS-IS Domain.
144. HOW DOES A ROUTER DETERMINE WHAT AREA IT IS IN?
Answer: The Portion Of The NET Preceding The Last Seven Octets Is The Area Address.
145. DOES IS-IS ELECT A BACKUP DESIGNATED ROUTER ON A BROADCAST SUBNETWORK?
Answer: IS-IS Does Not Elect A BDR.
146. WHAT IS THE PURPOSE OF THE PSEUDONODE ID?
Answer: The PSEUDONODE ID Is The Last Octet Of A LAN ID. Its Purpose Is To Distinguish LAN IDs Which Are Originated By A Single Router Which Is The DR On Multiple LANs.
147. WHAT IS THE MAXIMUM AGE (MAXAGE) OF AN IS-IS LSP?
Answer: The Maxage Of An IS-IS LSP Is 1200 Seconds (20 Minutes).
148. WHAT IS THE BASIC DIFFERENCE BETWEEN THE WAY OSPF AGES ITS LSAS AND THE WAY IS-IS AGES ITS LSPS?
Answer: OSPF Increments The Age Up To Maxage; IS-IS Decrements The Age Down To 0. A New OSPF LSA Has An Age Of 0, Whereas A New IS-IS LSP Has An Age Of Maxage.
149. HOW OFTEN DOES AN IS-IS ROUTER REFRESH ITS LSPS?
Answer: The Refresh Rate Of An IS-IS Router Is 900 Seconds (15 Minutes).
150. WHAT IS A COMPLETE SEQUENCE NUMBER PACKET (CSNP)? HOW IS IT USED?
Answer: A Complete Sequence Number Packet Contains A Full Listing Of All Lsps In A Database. A CSNP Is Periodically Sent By The Designated Router On A Broadcast Network To Maintain Database Synchronization.
151. WHAT IS A PARTIAL SEQUENCE NUMBER PACKET (PSNP)? HOW IS IT USED?
Answer: A Partial Sequence Number Packet Contains A Listing Of One Or More LSPs. It Has Two Uses: On Point-To-Point Networks, It Is Used To Acknowledge The Receipt Of LSPs. On Broadcast Networks, It Is Used To Request LSPs.
152. WHAT IS THE PURPOSE OF THE OVERLOAD (OL) BIT?
Answer: An IS-IS Router Uses The Overload Bit To Inform Its Neighbors That It Is Experiencing A Memory Overload And Cannot Store The Entire Link State Database.
153. WHAT IS THE PURPOSE OF THE ATTACHED (ATT) BIT?
Answer: The Attached Bit Is Used By L1/L2 Routers To Inform L1 Routers That It Is Attached To The L2 Backbone.
154. WHAT METRICS ARE SPECIFIED BY THE ISO FOR IS-IS? HOW MANY OF THESE METRICS DOES THE CISCO IOS SUPPORT?
Answer: The ISO Specifies Four Metrics: Default, Expense, Delay, And Error. Cisco Supports Only The Default Metric.
155. WHAT IS THE MAXIMUM VALUE OF THE IS-IS DEFAULT METRIC?
Answer: The Maximum Value Of Any Of The IS-IS Metrics Is 63.
156. WHAT IS THE MAXIMUM METRIC VALUE OF AN IS-IS ROUTE?
Answer: The Maximum Metric Value Of An IS-IS Route Is 1023.
157. WHAT IS THE DIFFERENCE BETWEEN A LEVEL 1 IS-IS METRIC AND A LEVEL 2 IS-IS METRIC?
Answer: L1 IS-IS Metrics Apply To Intra-Area Routes, And L2 IS-IS Metrics Apply To Inter-Area Routes.
158. WHAT IS THE DIFFERENCE BETWEEN AN INTERNAL IS-IS METRIC AND AN EXTERNAL IS-IS METRIC?
Answer: Internal Metrics Apply To Routes To Destinations Within The IS-IS Domain. External Metrics Apply To Routes To Destinations External To The IS-IS Domain.
†
Hands - On Experience Is An Invaluable Part Of Preparing For The Lab Exam And Never Pass Up An Opportunity To Configure Or Troubleshoot A Router ( If You Have Access To Lab Facilities, Take Full Advantage Of Them) There Is No Replacement For The Experience You Can Gain From Working In A Lab, Where You Can Configure Whatever You Want To Configure And Introduce Whatever Problems You Want To Introduce, Without Risk Of Disrupting A Production Network. Thank You And Best Of Luck
This Article Written Author By: Premakumar Thevathasan - CCNA, CCNP, MCSE, MCSA, MCSA - MSG, CIW Security Analyst, CompTIA Certified A+ And Etc.
◙ - ➤ Cisco Routing And Switching (PART – 1 With 501 Questions & Answers):
Some Topics That You Might Want To Pursue On Your Own That We Did Not Cover In This Article Are Listed Here. The Work Described In This Article Is Mainly Focused On The Field Of “IP ROUTING, IP ADDRESSES, RIP, EIGRP, OSPF, BGP, IS-IS”.
NETWORKING FOUNDATION BASIC CONCEPTS:
INTRODUCT ION:
A LOCAL AREA NETWORK Is Composed Of A Relatively Small Number Of Hosts Connected Over A Relatively Small Physical Area. “Relatively Small” Is The Important Phrase Here. To Give Some Meaning To The Term “Relatively,” Consider That A 10 Base T Ethernet (10 Megabit Per Second Using Twisted Pair Cabling) Has A Usual Maximum Of 1024 Stations Over A Maximum Cable Distance Of 2500 Meters. For Instance, A Typical Office LAN, Using 100 baset Ethernet, Might Have 100 Computers (And Printers) Attached To A Switch Or Set Of Hubs.
AN ETHERNET LOCAL AREA NETWORK (LAN) Is Essentially A (Logical) Bus Based Broadcast Network; Though The Physical Implementation May Use Hubs (With A Physical Star Topology). As One Would Expect, Broadcast LANs Must Deal With Collisions; Either By Preventing Them Or Detecting Them And Taking Appropriate Action. Token Based LANs Avoid Collisions By Only Allowing One Host At Time To Transmit (The Host That Currently Has The Token May Transmit).
Standards That Relate To LANs Are Primarily The IEEE 802.X Series. For Instance, 802.3 Is The Media Access Control (MAC) Standard For CSMA/CD (The Ethernet Standard); While 802.5 Is The MAC Standard For Token Ring. Just Above The MAC Level Is The Logical Link Control (802.2) Standard And Above That It The High Level Interface (802.1) Standard. Within A LAN, Addressing Is Done With A MAC Address. Between LANs Using TCP/IP, Addressing Is Done Using IP Addresses.
MEDIA: One Of The First Things Done When Setting Up A Network Of Routers, Switches, And Host Devices Is The Creation Of Connections Between The Devices. This Connection Is Done Via Media. The Media Can Be Either Bounded (Cables) Or Unbounded (Wireless).
When Data Is Transmitted Across Media, Operations Are Occurring At The Network Interface Layer. This Layer Includes Both The Physical Implementation (Cable Type, Wireless Frequency, Connectors, And So On) And The Communication Method Employed By The Media (Ethernet, 802.11, Frame Relay, PPP).
Media Is Usually Used To Connect Infrastructure Devices Such As Switches And Routers. Moreover, The Management Of Infrastructure Devices Is Typically Done Via Wire, And Not Wirelessly In Accordance With Security Best Practices.
NETWORK DATA MESSAGES: From A LAN And Convert Them Into Packets Suitable For Transmission Beyond The LAN On A Wide Area Network (WAN). The Goal Is Almost Always To Get These Packets To Another LAN And Ultimately To The Correct Host On That LAN. Part Of The “Conversion” Process Is To Add A Packet Header. Other Routers Will Generally Only Look At A Packet’s Header Information, Not At The Contents Or Data In The Packet.
ROUTER:
ROUTERS HAVE BEEN KNOWN BY SEVERAL NAMES. Back In Ancient Times When What Is Now The Internet Was Called The ARPANET, Routers Were Called IMPs, For Interface Message Processors. More Recently, Routers Were Called Gateways; Remnants Of This Nomenclature Can Still Be Found In Terms Such As Border Gateway Protocol (BGP) And Interior Gateway Routing Protocol (IGRP). In The Open System Interconnection (OSI) World, Routers Are Known As Intermediate Systems (IS).
Also Make Decisions About Where To Send These Packets, Based On: The Addresses Contained Within The Packet Headers And A Table Of Routes Maintained Within The Router.
Updating These Routing Tables And Forwarding Data Packets Between Portions Of A Network Are Two Of The Primary Tasks Of A Router.
Building Packets And Unwrapping Packets Are Additional Router Functions Performed By The First And Last Routers, Respectively, That A Message Passes Through.
IN ADDITION To Directing Packets, A Router May Be Responsible For Filtering Traffic, Allowing Some Packets To Pass Through And Rejecting Others. Filtering Can Be A Very Important Function Of Routers; It Allows Them To Help Protect Computers And Other Network Components. It Is Also Possible That At The Destination End A Router May Have To Break Large Packets Up To Accommodate The Size Limits Of The Destination LAN.
ROUTE TABLES: As Mentioned, One Of Tasks Of A Router Is To Maintain Route Tables Which Are Used To Decide Where A Packet Is To Go And Thus Which Interface It Should Be Sent Out. In The Past These Tables Were Built And Updated By Hand And This Is Referred To As Static Routing. In Dynamic Routing, The Router Learns About Where Various Addresses Are Relative To Itself And Builds Up Route Tables Based On This Information.
SPECIAL PURPOSE ROUTER: What Are Some Of The Motivations For Using A Dedicated, Purpose-Built Router Rather Than A General Purpose Machine With A “Standard” Operating System (OS)? A Special Purpose Router Can Have Much Higher Performance Than A General Purpose Computer With Routing Functionality Tacked Onto It. Also, One Can Potentially Add More Network Connections To A Machine Designed For That Purpose, Because It Can Be Designed To Support More Interface Card Slots. Thus, A Special Purpose Device Will Probably Be A Lower Cost Solution For A Given Level Of Functionality. But There Are Also A Number Of Security Benefits To A Special Purpose Router; In General, Consolidating Network Routing And Related Functions On A Dedicated Devices Restricts Access To And Limits The Exposure Of Those Critical Functions.
Like CISCO’S INTERNETWORK OPERATING SYSTEM (IOS) Can Be Smaller, Better Understood, And More Thoroughly Tested Than A General Purpose OS ( IOS Will Be Used In This Guide To Refer The Router’s Operating System And Associated Software, But Hardware Other Than Cisco Would Run Similar Software) .
AN INTERIOR ROUTER Forwards Traffic Between Two Or More Local Networks Within An Organization Or Enterprise. The Networks Connected By An Interior Router Often Share The Same Security Policy, And The Level Of Trust Between Them Is Usually High. If An Enterprise Has Many Interior Routers, They Will Usually Employ An Interior Gateway Protocol To Manage Routes. Interior Routers May Impose Some Restrictions On The Traffic They Forward Between Networks.
A BACKBONE OR EXTERIOR ROUTER Is One That Forwards Traffic Between Different Enterprises (Sometimes Called Different ‘Autonomous Systems’). The Traffic Between The Different Networks That Make Up The Internet Is Directed By Backbone Routers. The Level Of Trust Between The Networks Connected By A Backbone Router Is Usually Very Low. Typically, Backbone Routers Are Designed And Configured To Forward Traffic As Quickly As Possible, Without Imposing Any Restrictions On It. The Primary Security Goals For A Backbone Router Are To Ensure That The Management And Operation Of The Router Are Conducted Only By Authorized Parties, And To Protect The Integrity Of The Routing Information It Uses To Forward Traffic. Backbone Routers Typically Employ Exterior Gateway Protocols To Manage Routes.
A BORDER ROUTER Forwards Traffic Between An Enterprise And Exterior Networks. The Key Aspect Of A Border Router Is That It Forms Part Of The Boundary Between The Trusted Internal Networks Of An Enterprise, And Untrusted External Networks (E.G. The Internet). It Can Help To Secure The Perimeter Of An Enterprise Network By Enforcing Restrictions On The Traffic That It Controls. A Border Router May Employ Routing Protocols, Or It May Depend Entirely On Static Routes.
ROUTER HARDWARE:
There Are Typically A Number Of Types Of Memory In A Router Possibly Including: RAM, NVRAM, Flash, And ROM (PROM, EEPROM). These Are Listed Roughly In Order Of Volatility. The Mix Of Types And The Amount Of Each Type Are Determined On The Basis Of: Volatility, Ease Of Reprogramming, Cost, Access Speed, And Other Factors. ROM Is Used To Store A Router’s Bootstrap Software. Non-Volatile RAM (NVRAM) Is Used To Store The Startup Configuration That The IOS Reads When The Router Boots. Flash Memory Stores The IOS (Or Other Router OS), And If There Is Enough Flash It May Store More Than One Version Of IOS.
Interfaces Provide The Physical Connections From A Router To Networks. Interface Types Include Ethernet, Fast Ethernet, Gigibit-Ethernet, Token Ring, FDDI, Low-Speed Serial, Fast Serial, HSSI, ISDN BRI, Etc. Each Interface Is Named And Numbered. Interface Cards Fit Into Slots In A Router, And An External Cable Of The Appropriate Type Is Connected To The Card. In Addition To A Number Of Interfaces, Almost All Routers Have A Console Port Providing An Asynchronous Serial Connection (RS-232). Also, Most Routers Have An Auxiliary Port, Which Is Frequently Used For Connecting A Modem For Router Management.
ROUTER SOFTWARE:
The Startup Or Backup Configuration Is Stored In NVRAM. It Is Executed When The Router Boots. As Part Of The Boot Process A Copy Of This Configuration Is Loaded Into RAM. Changes Made To A Running Configuration Are Usually Made Only In RAM And Generally Take Effect Immediately. If Changes To A Configuration Are Written To The Startup Configuration, Then They Will Also Take Effect On Reboot. Changes Made Only To The Running Configuration Will Be Lost Upon Reboot.
An Operational Router Will Have A Large Number Of Processes Executing To Support The Services And Protocols That The Router Must Support. All Routers Support A Variety Of Commands That Display Information About What Processes Are Running And What Resources, Such As CPU Time And Memory, They Are Consuming. Unneeded Services And Facilities Should Be Disabled To Avoid Wasting CPU And Memory Resources, And To Avoid Giving Attackers Additional Potential Avenues For Attack.
Each Router Should Have A Unique Name To Identify It, And Each Interface Should Have Unique Network Addresses Associated With It. Basic Security Settings Should Be Established On Any Router Before It Is Connected To An Operational Network.
IP ROUTING AND IP ARCHITECTURES:
What Is Important To Keep In Mind Is That MAC Addresses Are Used Within A LAN. Each Device On The LAN Will Have A Something Like A Network Interface Card (NIC) Which Has A Unique MAC Address.
MAC ADDRESSES:
UNDERSTANDING IP ADDRESSES:
IP ADDRESS AND CLASS FACTS: IP ADDRESSES ALLOW HOSTS TO PARTICIPATE ON IP BASED NETWORKS. AN IP ADDRESS:
✓ Is A 32-Bit Binary Number Represented As Four Octets (Four 8-Bit Values). Each Octet Is Separated By A Period.
✓ IP Addresses Can Be Represented In One Of Two Ways:
◙ - ➤ Decimal (For Example 131.107.2.200). In Decimal Notation, Each Octet Must Be Between 0 And 255.
◙ - ➤ Binary (For Example 10000011.01101011.00000010.11001000). In Binary Notation,Each Octet Is An 8-Digit Number.
✓ The IP Address Includes Both The Network And The Host Address.
✓ Each IP Address Has An Implied Address Class That Can Be Used To Infer The Network Portion Of The Address.
✓ The Subnet Mask Is A 32-Bit Number That Is Associated With Each IP Address That Identifies The Network Portion Of The Address. In Binary Form, The Subnet Mask Is Always A Series Of 1's Followed By A Series Of 0's (1's And 0's Are Never Mixed In Sequence In The Mask). A Simple Mask Might Be 255.255.255.0.
IP ADDRESSES HAVE A DEFAULT CLASS. THE ADDRESS CLASS IDENTIFIES THE RANGE OF IP ADDRESSES AND A DEFAULT SUBNET MASK USED FOR THE RANGE ;
◙ CLASS A Address Range: 1.0.0.0 to 126.255.255.255, First Octet Range 1-126 (00000001--01111110 binary), Default Subnet Mask 255.0.0.0
◙ CLASS B Address Range: 128.0.0.0 to 191.255.255.255, First Octet Range 128-191(10000000--10111111 binary) Default Subnet Mask 255.255.0.0
◙ CLASS C Address Range: 192.0.0.0 to 223.255.255.255, First Octet Range 192-223 (11000000--11011111 binary) Default Subnet Mask 255.255.255.0
◙ CLASS D Address Range: 224.0.0.0 to 239.255.255.255, First Octet Range 224-239 (11100000--11101111 binary) Default Subnet Mask N/A
◙ CLASS E Address Range: 240.0.0.0 to 255.255.255.255, First Octet Range 240-255 (11110000--11111111 binary) Default Subnet MaskN/A
WHEN USING THE DEFAULT SUBNET MASK FOR AN IP ADDRESS, YOU HAVE THE FOLLOWING NUMBER OF SUBNET ADDRESSES AND HOSTS PER SUBNET:
◙ - ➤ There Are Only 126 Class A Network Ids (Most Of These Addresses Are Already Assigned) Each Class A Address Gives You 16,777,214 Hosts Per Network.
◙ - ➤ There Are 16,384 Class B Network Ids. Each Class B Address Gives You 65,534 Hosts Per Network.
◙ - ➤ There Are 2,097,152 Class C Network Ids. Each Class C Address Gives You 254 Hosts Per Network.
◙ - ➤ Class D Addresses Are Used For Multicast Groups Rather Than Network And Host Ids.
◙ - ➤ Class E Addresses Are Reserved For Experimental Use.
THE FOLLOWING ADDRESS RANGES HAVE BEEN RESERVED FOR PRIVATE USE:
◙ - ➤ 10.0.0.0 To 10.255.255.255
◙ - ➤ 172.16.0.0 To 172.31.255.255
◙ - ➤ 192.168.0.0 To 192.168.255.255
Use Addresses In These Ranges For Your Private Networks. Routers Connected To The Internet Typically Filter Messages Within These Ranges And Prevent Them From Being Propagated To The Internet.
LOCAL HOST ADDRESS: Addresses In The 127.0.0.0 Range Are Reserved For The Local Host (In Other Words "This"Host Or The Host You're Currently Working At). The Most Commonly-Used Address Is 127.0.0.1 Which Is The Loopback Address.
BROADCAST ADDRESS: The Last Address In The Range Is Used As The Broadcast Address And Is Used To Send Messages To All Hosts On The Network. In Binary Form, The Broadcast Address Has All 1's In The Host Portion Of The Address.
FOR EXAMPLE, ASSUMING THE DEFAULT SUBNET MASKS ARE USED:
◙ - ➤ 115.255.255.255 Is The Broadcast Address For Network 115.0.0.0
◙ - ➤ 154.90.255.255 Is The Broadcast Address For Network 154.90.0.0
◙ - ➤ 221.65.244.255 Is The Broadcast Address For Network 221.65.244.0
TWO OTHER FORMATS YOU MIGHT SEE FOR THE BROADCAST ADDRESS:
◙ - ➤ The Broadcast Address Might Also Be Designated By Setting Each Of The Network Address Bits To 0. For Example, 0.0.255.255 Is The Broadcast Address Of A Class B Address. This Designation Means "The Broadcast Address For This Network."
◙ - ➤ 255.255.255.255 Indicates A Broadcast Message Intended For All Hosts On This Network.
OSI MODEL:
Each Layer Provides A Set Of Functions To The Layer Above And, In Turn, Relies On The Functions Provided By The Layer Below. Although Messages Can Only Pass Vertically Through The Stack From Layer To Layer, From A Logical Point Of View, Each Layer Communicates Directly With Its Peer Layer On Other Nodes.
THE SEVEN LAYERS ARE:
◙ - ➤ Layer 7: Application Layer - > Deals with Network Applications Such As Terminal Emulation and File Transfer
◙ - ➤ Layer 6: Presentation Layer - > Deals With Formatting, Encryption, And Compression Of Data.
◙ - ➤ Layer 5: Session Layer - > Deals With Setup And Management Of Sessions Between Applications.
◙ - ➤ Layer 4: Transport Layer - > Deals With End To End Error Recovery And Delivery Of Complete Messages.
◙ - ➤ Layer 3: Network Layer - > Deals With Transmission Of Packets And Establishing Connections.
◙ - ➤ Layer 2: Data Link Layer - > Framing Of Units Of Information And Error Checking
◙ - ➤ Layer 1: Physical Layer - > Deals With Transmission Of A Bit Stream And Definition Of Physical Link.
Groups Of Protocols (Called Protocol Suites Or Protocol Stacks) Are Designed To Interact And Be Used Together. The TCP/IP Protocol Suite Is Used On The Internet And On Most Networks. Nearly All Computers Today Use TCP/IP Protocols For Communication Because It Is Highly Scalable And Routable. The Layers Of The DOD Model Are As Follows:
◙ - ➤ The Application Layer (Also Called The Process Layer) Corresponds To The Session, Presentation, And Application Layers Of The OSI Model.
◙ - ➤ The Host-To-Host Layer Is Comparable To The Transport Layer Of The OSI Model And Is Responsible For Error Checking And Reliable Packet Delivery. Here, The Data Stream Is Broken Into Segments That Must Be Assigned Sequence Numbers So That The Segments Can Be Reassembled Correctly On The Remote Side After They Are Transported.
◙ - ➤ The Internet Layer Is Comparable To The Network Layer Of The OSI Model. It Is Responsible For Moving Packets Through A Network. This Involves Addressing Of Hosts And Making Routing Decisions To Identify How The Packet Transverses The Network.
◙ - ➤ The Network Access Layer Corresponds To The Functions Of The Physical And Data Link Layers Of The OSI Model. It Is Responsible For Describing The Physical Layout Of The Network And How Messages Are Formatted On The Transmission Medium. Sometimes This Layer Is Divided Into The Network Access And The Physical Layer.
Note: The TCP/IP Model Focuses Specifically On The Functions In The Internet Layer And The Host-To-Host Layer.
DEVICE COMMUNICATION:
THE FOLLOWING FIVE-STEP DATA ENCAPSULATION PROCESS:
◙ - ➤ 1. Upper Layers Prepare The Data To Be Sent Through The Network.
◙ - ➤ 2. The Transport Layer Breaks The Data Into Pieces Called Segments, Adding Sequencing And Control Information.
◙ - ➤ 3. The Network Layer Converts The Segments Into Packets, Adding Logical Network And Device Addresses.
◙ - ➤ 4. The Data Link Layer Converts The Packets Into Frames, Adding Physical Device Addressing Information.
◙ - ➤ 5. The Physical Layer Converts The Frames Into Bits For Transmission Across The Transmission Media.
THE FOLLOWING SHORT DESCRIPTIONS CAN HELP YOU REMEMBER THE STEPS OF THE DATA ENCAPSULATION PROCESS:
◙ - ➤ Upper Layers -- > Data
◙ - ➤ Transport Layer -- >Segments
◙ - ➤ Network Layer -- > Packets Containing Logical Addresses
◙ - ➤ Data Link Layer -- > Framing That Adds Physical Addresses
◙ - ➤ Physical Layer -- > Bits
FRAME:
A STORAGE-AREA NETWORK (SAN):
WHICH Two Primary Port Authentication Protocols Are Used With VSANs?
Tips: (Virtual Storage Area Network (VSAN) Is A Collection Of Ports From A Set Of Connected Fibre Channel Switches, That Form A Virtual Fabric. Ports Within A Single Switch Can Be Partitioned Into Multiple VSANs, Despite Sharing Hardware Resources. Conversely, Multiple Switches Can Join A Number Of Ports To Form A Single VSAN. VSANs Were Designed By Cisco Systems, Modelled After The Virtual Local Area Network (VLAN) Concept In Ethernet Networking, Applied To A Storage Area Network. In October 2004, The Technical Committee T11 Of The International Committee For Information Technology Standards Approved VSAN Technology To Become A Standard Of The American National Standards Institute (ANSI)).
CHAP And DHCHAP Two primary port authentication protocols when working with VSANs:
CHALLENGE HANDSHAKE AUTHENTICATION PROTOCOL (CHAP):
CHAP Is The Mandatory Protocol For iSCCI (Internet Small Computer System Interface, An Internet Protocol (IP)-Based Storage Networking Standard For Linking Data Storage Facilities), As Chosen By The Internet Engineering Task Force (IETF). CHAP Is Based On Shared Secrets.
Diffie-HELLMAN CHALLENGE HANDSHAKE AUTHENTICATION PROTOCOL (DHCHAP):
DHCHAP May Be Used To Authenticate Devices Connecting To A Fibre Channel Switch. By Using Fibre Channel Authentication, You Allow Only Trusted Devices To Be Added To A Fabric. This Prevents Unauthorized Devices From Accessing The Fibre Channel Switch.
QUESTIONS AND ANSWERS
2. PROTOCOL?
3. PURPOSE OF A MAC PROTOCOL?
4. FRAME?
5. WHAT FEATURE IS COMMON TO ALL FRAME TYPES?
6. MAC ADDRESS / MAC IDENTIFIER?
7. WHY IS A MAC ADDRESS NOT A TRUE ADDRESS?
8. WHAT ARE THE THREE SOURCES OF SIGNAL DEGRADATION ON A DATA LINK?
Attenuation Is A Function Of The Resistance Of The Medium.
Interference Is A Function Of Noise Entering The Medium.
Distortion Is A Function Of The Reactive Characteristics Of The Medium, Which React Differently To Different Frequency Components Of The Signal.
9. PURPOSE OF A REPEATER?
10. PURPOSE OF A BRIDGE?
11. WHAT MAKES A TRANSPARENT BRIDGE TRANSPARENT?
It Can Then Refer To The Table When Deciding Whether To Filter Or Forward A Frame. The Bridge Is Transparent Because It Performs This Learning Function Independently Of The Devices That Originate The Frames. The End Devices Themselves Have No Knowledge Of The Bridge.
12. DIFFERENCES BETWEEN LANS AND WANS:
WANs Cover A Large Geographic Area, From Citywide To Worldwide.
LANs Usually Consist Entirely Of Privately Owned Components. Some Components Of A WAN, Such As A Packet Switching Network Or Point-To-Point Serial Links, Are Usually Leased From A Service Provider.
A LAN Provides High Bandwidth At A Relatively Cheap Price. The Bandwidth Across A WAN Is Significantly More Expensive.
13. WHAT IS THE PURPOSE OF A BROADCAST MAC IDENTIFIER? WHAT IS THE BROADCAST MAC IDENTIFIER, IN HEX AND IN BINARY?
14. PRIMARY SIMILARITY AND DIFFERENCE BETWEEN A BRIDGE AND A ROUTER?
The Difference Is That A Bridge Works By Interconnecting Separate Segments Of A Single Network, Whereas A Router Interconnects Separate Networks.
15. WHAT IS A PACKET? WHAT IS THE PRIMARY SIMILARITY AND DIFFERENCE BETWEEN A FRAME AND A PACKET?
The Similarity Between A Frame And A Packet Is That They Both Encapsulate Data And Provide An Addressing Scheme For Delivering The Data.
The Difference Between A Frame And A Packet Is That The Frame Delivers Data Between Two Devices Sharing A Common Data Link, Whereas A Packet Delivers Data Across A Logical Pathway, Or Route, Spanning Multiple Data Links.
16. AS A PACKET PROGRESSES ACROSS AN INTERNETWORK, DOES THE SOURCE ADDRESS CHANGE?
17. WHAT IS A NETWORK ADDRESS? WHAT IS THE PURPOSE OF EACH PART OF A NETWORK ADDRESS? Answer: Network Addresses Are The Addresses Used In Packets. Each Network Address Has A Network Part, Which Identifies A Particular Data Link, And A Host Or Node Part, Which Identifies A Specific Device On The Data Link Identified By The Network Part.
18. PRIMARY DIFFERENCE BETWEEN A NETWORK ADDRESS AND A DATA LINK IDENTIFIER?
19. OPEN SYSTEMS INTERCONNECTION (OSI) SEVEN LAYER AND PURPOSE OF EACH LAYER?
LAYER 7: Application Layer - ➤ Deals With Services Such As Email And File Transfer.
LAYER 6: Presentation Layer - ➤ Deals With Formatting, Encryption, And Compression Of Data.
LAYER 5: Session Layer- ➤ Deals With Setup And Management Of Sessions Between Applications.
Layer 4: Transport Layer - ➤ Deals With End To End Error Recovery And Delivery Of Complete Messages.
LAYER 3: Network Layer - ➤ Deals With Transmission Of Packets And Establishing Connections.
LAYER 2: Data Link Layer -- ➤ Deals With Transmission Of Packets On One Given Physical Link. How The Medium Is Accessed And Shared, How Devices On The Medium Are Identified, And How Data Is Framed Before Being Transmitted On The Medium.
LAYER 1: Physical Layer - ➤ Deals With Transmission Of A Bit Stream And Definition Of Physical Link.
Also The Five Layers Of The TCP/IP Protocol Suite Are The Following:
✓ Physical Layer - > The Physical Layer Contains The Protocols Of The Physical Medium.
✓ Data-Link Layer - > The Data Link Layer Contains The Protocols That Control The Physical Layer: How The Medium Is Accessed And Shared, How Devices On The Medium Are Identified, And How Data Is Framed Before Being Transmitted On The Medium.
✓ Internet (Or IP) Layer - > The Internet Layer Contains The Protocols That Define The Logical Grouping Of Data Links Into A Network And The Communication Across That Network.
✓ Host-To-Host Layer - > The Host-To-Host Layer Contains The Protocols That Define And Control The Logical, End-To-End Paths Across The Network.
✓ Application Layer - > The Application Layer Corresponds To The OSI Session, Presentation, And Application Layers.
IP ADDRESSES
21. WHAT IS FRAGMENTATION? WHAT FIELDS OF THE IP HEADER ARE USED FOR FRAGMENTATION?
The Data Within The Packet Will Be Broken Into Fragments, And Each Fragment Will Be Encapsulated In Its Own Packet. The Receiver Uses The Identifier And Fragment Offset Fields And The MF Bit Of The Flags Field To Reassemble The Fragments.
22. PURPOSE OF THE TTL FIELD IN THE IP HEADER? HOW DOES THE TTL PROCESS WORK?
Each Router Through Which The Packet Passes Will Decrement The Integer By One. If A Router Decrements The TTL To Zero, It Will Discard The Packet And Send An ICMP "Time Exceeded" Error Message To The Packet's Source Address.
23. WHAT IS THE FIRST OCTET RULE?
Class B: The First Two Bits Of The First Octet Are Always 10.
Class C: The First Three Bits Of The First Octet Are Always 110.
Class D: The First Four Bits Of The First Octet Are Always 1110.
Class E: The First Four Bits Of The First Octet Are Always 1111.
24. HOW ARE CLASS A, B, AND C IP ADDRESSES RECOGNIZED IN DOTTED DECIMAL? HOW ARE THEY RECOGNIZED IN BINARY?
A 0000000 - 01111110 1 - 126
B 10000000 - 10111111 128 - 191
C 11000000 - 11011111 192- 223
25. AN ADDRESS MASK, AND HOW DOES IT WORK?
26. WHAT IS A SUBNET? WHY ARE SUBNETS USED IN IP ENVIRONMENTS?
27. WHY CAN'T A SUBNET OF ALL ZEROS OR ALL ONES BE USED IN A CLASSFUL ROUTING ENVIRONMENT?
28. WHAT IS ARP?
29. WHAT IS PROXY ARP?
30. WHAT IS A REDIRECT?
31. WHAT IS THE ESSENTIAL DIFFERENCE BETWEEN TCP AND UDP?
TCP, Or Transmission Control Protocol, Provides A Connection-Oriented Service Over The Connectionless Internet Layer.
UDP, Or User Datagram Service, Provides A Connectionless Service.
32. WHAT MECHANISMS DOES TCP USE TO PROVIDE CONNECTION-ORIENTED SERVICE?
33. INSTEAD OF ARP, NOVELL NETWARE USES A NETWORK ADDRESS THAT INCLUDES A DEVICE'S MAC ADDRESS AS THE HOST PORTION. WHY CAN'T IP DO THIS?
34. Netware Has A Transport Layer Service Similar To TCP Called Sequenced Packet Exchange (SPX), But No Service Similar To UDP. Applications Requiring Connectionless Service Directly Access The Connectionless IPX At The Network Layer. --- WHAT PURPOSE DOES UDP SERVE BY PROVIDING A CONNECTIONLESS SERVICE ON TOP OF WHAT IS ALREADY A CONNECTIONLESS SERVICE?
35. WHAT INFORMATION MUST BE STORED IN THE ROUTE TABLE?
36. WHAT DOES IT MEAN WHEN A ROUTE TABLE SAYS THAT AN ADDRESS IS VARIABLY SUBNETTED?
37. WHAT ARE DISCONTIGUOUS SUBNETS?
IP ROUTING
◙ Routing Is The Act Of Moving Information Across A Network (With At Least One Node In Between.)
◙ Routing Occurs At Layer 3 Of The OSI Model (Network Layer).
◙ Routing Involves Two Basic Activities:
A. Determining Optimal Routing Paths
✓ Protocol Use Metrics For Evaluation Of Paths
✓ Routing Algorithms Initialize And Maintain Routing Tables (Contain Route Information)
B. Transporting Information Groups (Packets)
Routing Protocols Are Used In The Implementation Of Routing Algorithms To Facilitate The Exchange Of Routing Information Between Networks, Allowing Routers To Build Routing Tables Dynamically. In Some Cases, Routing Protocols Can Themselves Run Over Routed Protocols: For Example, BGP Runs Over TCP: Care Is Taken In The Implementation Of Such Systems Not To Create A Circular Dependency Between The Routing And Routed Protocols.
Routing Protocals Are:
✓ ROUTING INFORMATION PROTOCOL (RIP AND RIP II)
✓ OPEN SHORTEST PATH FIRST (OSPF)
✓ INTERMEDIATE SYSTEM TO INTERMEDIATE SYSTEM (IS-IS)
✓ INTERIOR GATEWAY ROUTING PROTOCOL (IGRP)
✓ CISCO'S ENHANCED INTERIOR GATEWAY ROUTING PROTOCOL (EIGRP)
✓ BORDER GATEWAY PROTOCOL (BGP).
A Routed Protocol Is Any Network Layer Protocol That Provides Enough Information In Its Network Layer Address To Allow A Packet To Be Forwarded From One Host To Another Host Based On The Addressing Scheme, Without Knowing The Entire Path From Source To Destination. Routed Protocols Define The Format And Use Of The Fields Within A Packet. Packets Generally Are Conveyed From End System To End System. Almost All Network Layer Protocols And Those That Are Layered Over Them Are Routable, With IP Being An Example.
Data Link Protocols Such As Ethernet Are Necessarily Non-Routable Protocols, Since They Contain Only A Link-Layer Address, Which Is Insufficient For Routing: Some Higher-Level Protocols Based Directly On These Without The Addition Of A Network Layer Address, Such As 'Netbios', Are Also Non-Routable.
A Routing Metric Consists Of Any Value Used By Routing Algorithms To Determine To Choose One Route Over Another. Metrics Can Take Into Account Such Information As Bandwidth, Delay, Hop Count, Load, MTU, Reliability, And Cost. The Routing Table Stores Only The Best Possible Routes, While Link-State Or Topological Databases May Store All Other Information As Well.
Routers Use The Feature Known As Administrative Distance To Select The Best Path When They "Know" Of Two Or More Different Routes To The Same Destination From Two Different Routing Protocols. Administrative Distance Defines The Reliability Of A Routing Protocol. Each Routing Protocol Gets Prioritized In Order Of Most To Least Reliable Using An Administrative-Distance Value. A Static Route Has A Lower (Better) Administrative-Distance Than A Route By OSPF, Which Is Better Than RIP.
38. WHAT COMMAND IS USED TO EXAMINE THE ROUTE TABLE IN A CISCO ROUTER?
39. WHAT ARE THE TWO BRACKETED NUMBERS ASSOCIATED WITH THE NON-DIRECTLY CONNECTED ROUTES IN THE ROUTE TABLE?
40. WHEN STATIC ROUTES ARE CONFIGURED TO REFERENCE AN EXIT INTERFACE INSTEAD OF A NEXT-HOP ADDRESS, IN WHAT WAY WILL THE ROUTE TABLE BE DIFFERENT?
41. WHAT IS A SUMMARY ROUTE? IN THE CONTEXT OF STATIC ROUTING, HOW ARE SUMMARY ROUTES USEFUL?
42. WHAT IS AN ADMINISTRATIVE DISTANCE?
43. WHAT IS A FLOATING STATIC ROUTE?
44. WHAT IS THE DIFFERENCE BETWEEN EQUAL-COST AND UNEQUAL-COST LOAD SHARING?
✓ Equal-Cost Load Sharing Distributes Traffic Equally Among Multiple Paths With Equal Metrics.
✓ Unequal-Cost Load Sharing Distributes Packets Among Multiple Paths With Different Metrics. The Traffic Will Be Distributed Inversely Proportional To The Cost Of The Routes.
45. HOW DOES THE SWITCHING MODE AT AN INTERFACE AFFECT LOAD SHARING?
46. WHAT IS A RECURSIVE TABLE LOOKUP?
47. WHAT IS A ROUTING PROTOCOL?
48. WHAT BASIC PROCEDURES SHOULD A ROUTING ALGORITHM PERFORM?
✓ Passing Reachability Information About Networks To Other Routers,
✓ Receiving Reachability Information From Other Routers, Determining Optimal Routes Based On The Reachability Information It Has And For Recording This Information In A Route Table Reacting To, Compensating For, And Advertising Topology Changes In An Internetwork.
49. WHY DO ROUTING PROTOCOLS USE METRICS?
50. WHAT IS CONVERGENCE TIME?
51. WHAT IS LOAD BALANCING? NAME FOUR DIFFERENT TYPES OF LOAD BALANCING.
✓ Equal Cost, Per Packet
✓ Equal Cost, Per Destination
✓ Unequal Cost, Per Packet
✓ Unequal Cost, Per Destination
52. WHAT IS A DISTANCE VECTOR ROUTING PROTOCOL?
53. NAME SEVERAL PROBLEMS ASSOCIATED WITH DISTANCE VECTOR PROTOCOLS.
A Susceptibility To Incorrect Routing Information Because Of Its Dependence On Neighbors For - >
✓ Correct Information
✓ Slow Convergence
✓ Route Loops
✓ Counting To Infinity
54. WHAT ARE NEIGHBORS?
55. WHAT IS THE PURPOSE OF ROUTE INVALIDATION TIMERS?
56. EXPLAIN THE DIFFERENCE BETWEEN SIMPLE SPLIT HORIZON AND SPLIT HORIZON WITH POISONED REVERSE.
✓ Simple Split Horizon Does Not Send Route Information Back To The Source Of The Route Information.
✓ Split Horizon With Poisoned Reverse Sends The Information Back To The Source But Sets The Metric To Unreachable.
57. WHAT IS THE COUNTING-TO-INFINITY PROBLEM, AND HOW CAN IT BE CONTROLLED?
58. WHAT ARE HOLDDOWN TIMERS, AND HOW DO THEY WORK?
This Approach Prevents The Router From Accepting Possibly Bad Routing Information While The Internetwork Is Reconverging.
59. WHAT ARE THE DIFFERENCES BETWEEN DISTANCE VECTOR AND LINK STATE ROUTING PROTOCOLS?
Distance Vector Protocols Usually Use A Variant Of The Bellman-Ford Algorithm To Calculate Routes,
✓ A Link State Router Sends Only Information About Its Directly Connected Links, But It Floods The Information Throughout The Internetworking Area.
And Link State Protocols Usually Use A Variant Of The Dijkstra Algorithm To Calculate Routes.
60. WHAT IS THE PURPOSE OF A TOPOLOGICAL DATABASE?
61. EXPLAIN THE BASIC STEPS INVOLVED IN CONVERGING A LINK STATE INTERNETWORK?
✓ All Routers Store All Received Copies Of The Link State Advertisement In A Link State Database.
✓ Each Router Calculates A Shortest Path Tree From The Information In The Topological Database And Enters Routes In Its Routing Tables Based On The Shortest Path Tree.
62. WHY ARE SEQUENCE NUMBERS IMPORTANT IN LINK STATE PROTOCOLS?
63. WHAT PURPOSE DOES AGING SERVE IN A LINK STATE PROTOCOL?
64. EXPLAIN HOW AN SPF ALGORITHM WORKS?
✓ The Lowest-cost Link To A Neighbor Becomes A Branch Of The Tree, And That Router's Neighbors Are Added To The List. The List Is Checked For Duplicate Paths, And If They Exist, The Higher-Cost Paths Are Removed From The List.
✓ The Lowest-Cost Router On The List Is Added To The Tree, That Router's Neighbors Are Added To The List, And The List Is Again Checked For Duplicate Paths. This Process Continues Until No Routers Remain On The List.
65. HOW DO AREAS BENEFIT A LINK STATE INTERNETWORK?
66. WHAT IS AN AUTONOMOUS SYSTEM?
67. WHAT IS THE DIFFERENCE BETWEEN AN INTERIOR GATEWAY PROTOCOL (IGP) AND AN EXTERIOR GATEWAY PROTOCOL (EGP)?
✓ An Exterior Gateway Protocol Is A Routing Protocol That Routes Between Autonomous Systems.
RIP
• Request For Comments (RFC) 1058
• Internet Standard (STD)
✓ It Uses Distance Vectors To Mathematically Compare Routes To Identify The Best Path To Any Given Destination Address
✓ With The Expansion Of IP Based Networks (More Numerous And Greater In Size)
✓ Update In 1994
✓ RIP2 Defined In 1994 In RFC 1723
✓ The Routing Information Protocol (RIP) Is A Distance-Vector, Interior Gateway (IGP) Routing Protocol Used By Routers To Exchange Routing Information.
✓ RIP Uses The Hop Count As A Routing Metric.
✓ RIP Prevents Routing Loops By Implementing A Limit On The Number Of Hops Allowed In A Path From The Source To A Destination. The Maximum Number Of Hops Allowed For RIP Is 15.
This Hop Limit, However, Also Limits The Size Of Networks That RIP Can Support.RIP Version 2 (RIPv2) Was Developed Due To The Deficiencies Of The Original RIP.
DIFFERENCE BETWEEN RIPv1 Vs RIPv2:
✓ In RIPv1, Subnet Masks Are NOT Included In The Routing Update And In RIPv2 Subnet Masks Are Included In The Routing Update.
✓ RIPv2 Multicasts The Entire Routing Table To All Adjacent Routers At The Address 224.0.0.9, As Opposed To RIPv1 Which Uses Broadcast (255.255.255.255). Unicast Addressing Is Still Allowed For Special Applications.
BASIC CONFIGURATION:
✓ The "Network" Command Is Used To Specify The Directly Connected Subnets On The Router To Be Configured And That Are Intended To Be Included In The Routing Updates.
✓ According To The Classful, Network Specified, The Subnets Of That Network Are Automatically Identified And Participate In The Routing Update. By Default Routing Updates Are Summarized At Network Boundaries.
✓ In RIPv2 This Auto Summarization Behavior Can Be Turned Off Using The "No Auto-Summary" Command. Moreover, Manual Summarization Can Be Configured On A Per Interface Level.
CONFIGURATION EXAMPLE:
R1(Config)#Router Rip
R1(Config-Router)#Version 2
R1(Config-Router)#Network 192.168.12.0
R1(Config-Router)#Exit
RIP VERIFICATION:
68. WHAT PORT DOES RIP USE?
69. WHAT METRIC DOES RIP USE? HOW IS THE METRIC USED TO INDICATE AN UNREACHABLE NETWORK?
70. WHAT IS THE UPDATE PERIOD FOR RIP?
71. HOW MANY UPDATES MUST BE MISSED BEFORE A ROUTE ENTRY WILL BE MARKED AS UNREACHABLE?
72. WHAT IS THE PURPOSE OF THE GARBAGE COLLECTION TIMER?
73. WHY IS A RANDOM TIMER ASSOCIATED WITH TRIGGERED UPDATES? WHAT IS THE RANGE OF THIS TIMER?
74. WHAT IS THE DIFFERENCE BETWEEN A RIP REQUEST MESSAGE AND A RIP RESPONSE MESSAGE?
75. WHICH TWO TYPES OF REQUEST MESSAGES DOES RIP USE?
76. UNDER WHAT CIRCUMSTANCES WILL A RIP RESPONSE BE SENT?
77. WHY DOES RIP HIDE SUBNETS AT MAJOR NETWORK BOUNDARIES?
✓ If A Router Does Not Have An Attachment To A Particular Major Network Address, It Has No Way To Know How That Major Network Is Subnetted. Therefore, No Subnets Of A Major Network Address Can Be Advertised Into Another Major Network.
IGRP
IGRP Is A Proprietary Protocol. IGRP Was Created In Part To Overcome The Limitations Of RIP (Maximum Hop Count Of Only 15, And A Single Routing Metric) When Used Within Large Networks. IGRP Supports Multiple Metrics For Each Route, Including Bandwidth, Delay, Load, MTU, And Reliability; To Compare Two Routes These Metrics Are Combined Together Into A Single Metric, Using A Formula Which Can Be Adjusted Through The Use Of Pre-Set Constants. By Default, The IGRP Composite Metric Is A Sum Of The Segment Delays And The Lowest Segment Bandwidth. The Maximum Hop Count Of IGRP-Routed Packets Is 255 (Default 100), And Routing Updates Are Broadcast Every 90 Seconds (By Default). IGRP Uses Port Number 9 For Communication.
IGRP Is Considered A Classful Routing Protocol. Because The Protocol Has No Field For A Subnet Mask, The Router Assumes That All Subnetwork Addresses Within The Same Class A, Class B, Or Class C Network Have The Same Subnet Mask As The Subnet Mask Configured For The Interfaces In Question. This Contrasts With Classless Routing Protocols That Can Use Variable Length Subnet Masks. Classful Protocols Have Become Less Popular As They Are Wasteful Of IP Address Space.
78. WHICH UDP PORT NUMBER IS USED TO ACCESS IGRP?
79. WHAT IS THE MAXIMUM IGRP INTERNETWORK DIAMETER, IN HOPS?
80. WHAT IS THE DEFAULT UPDATE PERIOD FOR IGRP?
81. WHY DOES IGRP SPECIFY AN AUTONOMOUS SYSTEM NUMBER?
82. WHAT IS THE DEFAULT IGRP HOLDDOWN TIME?
83. WHICH VARIABLES CAN IGRP USE TO CALCULATE ITS COMPOSITE METRIC?
84. HOW MANY ENTRIES CAN BE CARRIED WITHIN A SINGLE IGRP UPDATE PACKET?
RIPV2
85. WHICH THREE FIELDS ARE NEW TO THE RIPV2 MESSAGE FORMAT?
86. BESIDES THE EXTENSIONS DEFINED BY THE THREE FIELDS OF QUESTION 1, WHAT ARE THE OTHER TWO MAJOR CHANGES FROM RIPV1?
87. WHAT IS THE MULTICAST ADDRESS USED BY RIPV2? WHAT IS THE ADVANTAGE OF MULTICASTING MESSAGES OVER BROADCASTING THEM?
88. WHAT IS THE PURPOSE OF THE ROUTE TAG FIELD IN THE RIPV2 MESSAGE?
89. WHAT IS THE PURPOSE OF THE NEXT HOP FIELD?
90. WHAT IS THE UDP PORT NUMBER USED BY RIPV2?
91. WHICH ONE FEATURE MUST A ROUTING PROTOCOL HAVE TO BE A CLASSLESS ROUTING PROTOCOL?
92. WHICH ONE FEATURE MUST A ROUTING PROTOCOL HAVE TO USE VLSM?
93. WHICH TWO TYPES OF AUTHENTICATION ARE AVAILABLE WITH CISCO'S RIPV2? ARE THEY BOTH DEFINED IN RFC 1723?
EIGRP
EIGRP Is An Efficient But Proprietary Solution For Large Networks. Its Ability To Scale Is Limited Only By The Design Of The Network.
EIGRP Features And Advantages: The Goal Of EIGRP Is To Solve The Scaling Limitations That IGRP Faces, While Keeping The Advantages Of Distance Vector Routing Protocols: Simplicity, Economy Of Memory, And Economy Of Processor Resources. EIGRP Is Scalable In Terms Of Hardware Resources And Network Capacity. EIGRP Is Also Lightning Fast.
CISCO IDENTIFIES FOUR PRINCIPAL COMPONENTS OF EIGRP:
Protocol-Dependent Modules — EIGRP Supports Several Routed Protocols Independently. The Two That Are Of Interest Today Are Ip And IPv6.
Reliable Transport Protocol —EIGRP Sends Some Packets Reliably Using A Reliable Transport Protocol.
Neighbor Discovery And Recovery — EIGRP Uses Hellos To Identify Its Neighbors Quickly And To Recognize When Those Neighbors Are Down.
Diffusing Update Algorithm (DUAL)— DUAL Identifies The Procedure Used To Sort The List Of Available Paths And Select Best Paths And Feasible Fail-Over Routes.
EIGRP HAS THE FOLLOWING CHARACTERISTICS:
✓ Distance-Vector Protocol That Uses Some Link-State Features
✓ Event Triggered Updates
✓ Fast Convergence
✓ Cisco Proprietary
✓ Easy To Configure
✓ Automatic Redistribution Into IGRP
94. IS EIGRP A DISTANCE VECTOR OR A LINK STATE ROUTING PROTOCOL?
95. WHAT IS THE MAXIMUM CONFIGURED BANDWIDTH EIGRP WILL USE ON A LINK? CAN THIS PERCENTAGE BE CHANGED?
96. HOW DO EIGRP AND IGRP DIFFER IN THE WAY THEY CALCULATE THE COMPOSITE METRIC?
97. WHAT ARE THE FOUR BASIC COMPONENTS OF EIGRP?
✓ The Protocol Dependent Modules
✓ The Reliable Transport Protocol
✓ The Neighbor Discovery And Recovery Module
✓ The Diffusing Update Algorithm
98. IN THE CONTEXT OF EIGRP, WHAT DOES THE TERM RELIABLE DELIVERY MEAN? WHICH TWO METHODS ENSURE RELIABLE DELIVERY OF EIGRP PACKETS?
99. WHICH MECHANISM ENSURES THAT A ROUTER IS ACCEPTING THE MOST RECENT ROUTE ENTRY?
100. WHAT IS THE MULTICAST IP ADDRESS USED BY EIGRP?
101. WHAT ARE THE PACKET TYPES USED BY EIGRP?
✓ Hellos
✓ Acknowledgments
✓ Updates
✓ Queries
✓ Replies
102. AT WHAT INTERVAL, BY DEFAULT, ARE EIGRP HELLO PACKETS SENT?
103. WHAT IS THE DEFAULT HOLD TIME?
104. WHAT IS THE DIFFERENCE BETWEEN THE NEIGHBOR TABLE AND THE TOPOLOGY TABLE?
The Topology Table Lists All Known Routes That Have Feasible Successors.
105. WHAT IS A FEASIBLE DISTANCE?
106. WHAT IS THE FEASIBILITY CONDITION?
Another Way To Describe This Is That The Neighbor Is "Downstream" Relative To The Destination.
107. WHAT IS A FEASIBLE SUCCESSOR?
108. WHAT IS A SUCCESSOR?
109. WHAT IS THE DIFFERENCE BETWEEN AN ACTIVE ROUTE AND A PASSIVE ROUTE?
Answer: The Route Is Passive When There Are No Outstanding Queries.
110. WHAT CAUSES A PASSIVE ROUTE TO BECOME ACTIVE?
111. WHAT CAUSES AN ACTIVE ROUTE TO BECOME PASSIVE?
112. WHAT DOES STUCK-IN-ACTIVE MEAN?
A Response With An Infinite Metric Is Entered On The Neighbor's Behalf To Satisfy DUAL, And The Neighbor Is Deleted From The Neighbor Table.
113. WHAT IS THE DIFFERENCE BETWEEN SUBNETTING AND ADDRESS AGGREGATION?
Address Aggregation Is The Practice Of Summarizing A Group Of Network Or Subnet Addresses With A Single IP Network Address.
OSPF
Why We Are Calling OSPF Is A Link State Routing Protocol. Unlike RIP, OSPF Is Not Only Sending The Routing Updates To Its Neighbors. It Is Sending All The Information About The Link Like IP Address Of The Interface And Subnet Mask, The Type Of Network It Is Connected To (P2P Or P2Multi-Point Or FR) And The Routers Which Is Connected To It. The Collection Of These Link States Will Form A Link State Database.
OSPF Vs RIP: Comparison between RIP Vs OSPF is given below.
◙ - ➤ RIP Doesn’t Support For VLSM.
◙ - ➤ Periodic Update Of Routing Table Consumes Lots Of Bandwidth Especially On WAN Clouds.
◙ - ➤ RIP Converges Slower Than OSPF Does.
◙ - ➤ RIP Network Is A FLAT Network. Here No Concept Of Areas & Boundaries & Summarization.
OSPF
◙-◙ Can Use VLSM
◙-◙ Converges Quickly
◙-◙ Can Divide Into Areas. This Will Help Us To Use Summarization.
◙-◙ Allows Authentication.
◙-◙ It Uses Dijkstra’s Algorithm (SPF Algorithm) Reducing The Usage Of BW, By Sending Triggered Updates To Announce The Network Changes.
◙-◙ Sending Periodic Updates On Long Intervals (30 Mins).
Unlike RIP, OSPF Doesn’t Send Any Routing Updates On Periodic Intervals. It Will Only Send Triggered Updates. It Means Every Time It Doesn’t Send Full Routing Table To Its Neighbors. Whenever Any Changes In Network, Like New Router Added Or A Router Removed From The Network, It Will Send Information About That Particular Network To Its Neighbor.
TYPES OF TABLES USED IN OSPF.
2. Topology Table
3. Routing Table
◙ - ➤ NEIGHBOR TABLE: The Router Tracks All The Neighbors Which Is Running OSPF As A Routing Protocol And Put That Information In This Table. It Contains All The Information About The Directly Connected Neighbors. Like Their Router Id, To Which Network They Are Connected, And Which Network They Are Advertising. It Will Exchange Routing Information With Routers Which Is In This Table.
◙ - ➤ TOPOLOGY TABLE: This Is The One Of The Big Difference Between Distance Vector And Link-State Protocols. Distance Vector Protocol Doesn’t Have This Topology Table. They Only Know About The Directly Connected Neighbors. This Table Is A Road Map For Each And Every Single Network Which Is Available In A Particular Area. All The Routers In A Particular Area Will Be Having The Same Type Of Topology Table.
◙ - ➤ ROUTING TABLE: This Table Contains All The Best Routes To Reach A Particular Network. Based On The Topology Table It Will Be Having Multiple Paths For A Single Destination Network. It Will Run The Spf Algorithm To Find The Best Routes For Each And Every Network.
The Algorithm Places Each Router At The Root Of A Tree And Calculates The Shortest Path To Each Destination Based On The Cumulative Cost Required To Reach That Destination. Each Router Will Have Its Own View Of The Topology Even Though All The Routers Will Build A Shortest Path Tree Using The Same Link-State Database.
HOW TO CALCULATE OSPF COST? Interface Cost Is Derived From The Bandwidth. Formula Is:
Cost = Reference / Bandwidth.
By default, Reference is 100000 [ Kb/s ].
So, For Your Bandwidth Of 5120, Cost Should Be:
Cost = 100000 / 5120 = 19.53. Rounded Down To The Closest Integer, It's 19.
If You Want To Have Cost Of 51, You Would Need To Recalculate Your Bandwidth:
51 = 100000 / x => x= 100000 / 51 = 1960.78. Round it down to 1960.
THE CHARACTERISTICS OF OSPF AREA: Areas Are Similar To Subnets In That Routes & Networks Which Can Be Summarized Easily.
◙-◙ Each Area Can Contain N Number Of Routers.
◙-◙ All The Areas Should Connect To Area 0(Backbone Area)
◙-◙ All The Routers Within The Same Area Will Be Having The Same Topology Table
◙-◙ It Contains One Autonomous System Border System ROUTER(ASBR)
◙-◙ While Creating Multiple Areas In OSPF, We Should Create Area 0 (Backbone Area) First And Then Only We Should Create Other Areas. But All The Areas Should Connect To Area 0.
◙-◙ The Routers Which Will Be Having Only One SPF Link Database Are Called Internal Router (IR).
◙-◙ The Routers Those Which Have Interfaces In Multiple Areas Are Called Area Border Router (ABR).
◙-◙ A Router Which Connects, OSPF With Other Routing Protocol Is Called As Autonomous System Border Router (ASBR).
◙-◙ A Router Which Is Only In Area 0 Or Backbone Area Is Known As Backbone Area Router.
TYPES OF AREAS: There Are Five Types Of Areas Are There In OSPF, Which Is Listed Below:
◙ Stub Area
◙ Totally Stub Area
◙ No So Stubby Area
◙ Backbone Area
WHY WE ARE DIVIDING NETWORKS INTO MULTIPLE AREAS?
◙ It Requires A Hierarchical Design In IP Address Allocation.
◙ ABR & ASBR Are The Only Two Router Types Where We Can Do Summarization.
Let’s Consider We Are Running A Company With 100 Routers. We Are Using OSPF As An Internal Routing Protocol. All The Routers Which Are Running OSPF Will Be Having Same Topology Of The Entire Network. If Any Link Goes Down At Any Point Of Network, All The Routers Will Come To Know About That Link Failure. Then All The Routers Will Run SPF Algorithm To Find An Alternative Path To Reach The Other Networks. It Will Take More Time To Converge And To Calculate An Alternative Path If The Network Is Large. The Purpose Of Area Is To Minimize This.
If We SPLIT Those 100 Routers Into 2 Areas, Say Area 1 & Area 2 And Each Area Contains 50 Routers. And Both The Areas Are Connected To Area 0.In This Scenario Area 1 Doesn’t Care Any Change Happens In Area 2.If Any Link In Area 2 Goes Down That Will Be Localized Within Area 2.Only Those Which Are In Area 2 Need To Run SPF To Find The Alternative Path. Area 1 Doesn’t Care, Even Doesn’t Know About That Link Failure, Which Occurs In Area 2. So The OSPF Converges Quickly. It Is More Processor Efficient.
OSPF NEIGHBOR RELATIONSHIPS: Routers That Share A Common Segment Become Neighbors On That Segment. Neighbors Are Elected Via The Hello Protocol. Hello Packets Are Sent Periodically Out Of Each Interface Using IP Multicast. Routers Become Neighbors As Soon As They See Themselves Listed In The Neighbor's Hello Packet.
TWO ROUTERS WILL NOT BECOME NEIGHBORS UNLESS THEY AGREE ON THE FOLLOWING:
◙ They Need To Have Same Mask.
◙ Hello And Dead Timers Should Be Same On Both The Routers.
◙ Password Should Be Same On Both The Routers, If Authentication Is Enabled.
◙ - ► OSPF PACKET TYPES:
✓ HELLO –➤ Discovers Neighbors And Builds Adjacencies Between Them
✓ DATABASE DESCRIPTION (DBD) –➤ Checks For Db Synchronization Between Routers By Sending A Summary List Of All Routes In DB
✓ LINKS STATE REQUEST (LSR) –➤ Requests Specific Link State Records From Another Router
✓ LINK STATE UPDATE (LSU) –➤ Sends Specifically Requested Link State Requests
✓ LINK STATE ACKNOWLEDGEMENT (LSACK) –➤ Acknowledges The Other Packet Types
TO DISCOVER THE NEIGHBOR, OSPF WILL SEND HELLO PACKETS VIA THE OSPF ENABLED INTERFACE. THIS HELLO PACKET CONTAINS THE FOLLOWING INFORMATION.
◙ Router ID
◙ Hello And Dead Timers
◙ Network Mask
◙ Area ID
◙ Router Priority
◙ DR & BDR IP Address
ROUTER ID:
◙ The Router Id Is Nothing But The Router’s Name In The Ospf Process.
◙ Highest Active Interface Will Become Router ID.
◙ Loopback Beats Physical Interface.
HELLO AND DEAD TIMERS:
◙ OSPF Exchanges Hello Packets On Each Segment. This Is A Form Of Keepalive Used By Routers To Acknowledge Their Existence On A Segment.
◙ The Dead Interval Is The Number Of Seconds That A Router's Hello Packets Have Not Been Received Before Its Neighbors Consider To Be Down.
◙ Hello Packets Are Sent Once In Every 10 Secs On Broadcast/Point To Point Network & 30 Secs On Non Broadcast Multi-Access.
OSPF ADJACENCIES: The Adjacency Building Process Takes Effect After Multiple Stages Have Been Fulfilled. Routers That Become Adjacent Will Have The Exact Link-State Database. The Following Is A Brief Summary Of The States An Interface Passes Through Before Becoming Adjacent To Another Router:
DOWN: Hello Packets Have Been Sent The Router Is Waiting To Hear The Response From The Routers To Which It Sent Hello Packets.
ATTEMPT: This State Indicates That No Recent Information Has Been Received From The Neighbor. An Effort Should Be Made To Contact The Neighbor By Sending Hello Packets At The Reduced Rate Poll Interval.
INIT: The Interface Has Detected A Hello Packet Coming From A Neighbor But Bi-Directional Communication Has Not Yet Been Established. It Means The Router Needs To Acknowledge.
TWO-WAY: There Is Bi-Directional Communication With A Neighbor. The Router Has Seen Its Router Id In The Hello Packets Coming From A Neighbor. With This Info The Router Will Know That Whether It Is A New Neighbor Or Reply From An Old Neighbor.
At The End Of This Stage The Dr And BDR Election Would Be Done. At The End Of The 2way Stage, Routers Will Decide Whether We Can Build An Adjacency Or Not. The Decision Is Based On DR& BDR And The Type Of Network With Which Is Connected To.
EXSTART: Now Routers Are Trying To Establish The Initial Sequence Number That Is Going To Be Used In The Information Exchange Packets. The Sequence Number Is Used To Get The Most Recent Information.
EXCHANGE: Routers Will Send Their Whole Link-State Database By Sending Database Description Packets (DBD).In This Stage Router Won’t Send Its Entire Database To Its Neighbors. It Will Send Only Notes Of The Routing Table.
LOADING: At This State, Routers Have Built A Link-State Request List And A Link-State Retransmission List. Based On The DBD, If Any Information That Looks Incomplete Will Be Put On The Request List. Any Update That Is Sent Will Be Put On The Retransmission List Until It Gets Acknowledged.
FULL: At This State, The Adjacency Is Complete. The Neighboring Routers Are Fully Adjacent. Adjacent Routers Will Have A Similar Link-State Database.
After Sharing The Link-State Database The OSPF Will Start To Calculate The Best Path For Each And Every Network. This Is The Time To Run The SPF Algorithm. Once It Finds The Best Path To Each And Every Network, It Will Put Those Routes Into Its Routing Table. Till The Link Which Is In Routing Table Goes Down, OSPF Will Never Run SPF.
ADJACENCY BEHAVIOR IN POINT-TO-POINT LINKS:
◙ OSPF Packets Sent Using A Destination Address Of 224.0.0.5
ADJACENCY BEHAVIOR IN BROADCAST MULTIACCESS NETWORKS:
◙ DR And BDR Selection Are Required
◙ All Neighbor Routers Form Adjacencies With DR And BDR Only
◙ Packets To The DR And BDR Are Addressed To 224.0.0.6
◙ Packets From DR To All Other Routers Is 224.0.0.5
OSPF OVER FRAME-RELAY – FIVE MODES OF OSPF OPERATION ARE AVAILABLE
BROADCAST – CISCO EXTENSION:
◙ Has One IP Subnet
◙ Uses Multicast OSPF Hello Packets To Discover Neighbors
◙ Elects Dr And BDR
◙ Requires A Full-Mesh Or Partial-Mesh Topology
NONBROADCAST (NBMA) – RFC 2328
◙ Has One IP Subnet
◙ Requires Neighbors To Be Manually Configured
◙ Elects Dr And BDR
◙ Requires That The DR And BR Have Full Connectivity With All Other Routers
◙ Typically Used In A Full-Mesh Or Partial-Mesh Topology
POINT-TO-MULTIPOINT – RFC 2328
◙ Has One IP Subnet
◙ Uses Multicast OSPF Hello Packets To Discover Neighbors
◙ Does Not Require Dr And BDR
◙ Typically Used In A Partial-Mesh Or Star Topology
POINT-TO-MULTIPOINT NONBROADCAST – CISCO EXTENSION
◙ Used In Place Of RFC Compliant Point-To-Multipoint If Multicast And Broadcast Are Not Enabled On The Virtual Circuit
◙ Requires Neighbors To Be Manually Configured
◙ Does Not Require Dr And BDR
POINT-TO-POINT – CISCO EXTENSION:
◙ Unique Subnet On Each Subinterface
◙ Does Not Have DR And BDR
◙ Used When Only Two Routers Need To Form An Adjacency On A Pair Of Interfaces
◙ Can Be Used With Either Lan Or Wan Interfaces
LSA TYPES:
◙ Type 1 – Router LSAS: – Generated By Every Router In An Area And Does Not Cross An ABR
◙ Type 2 – Network LSAS: – Advertised By Dr And Does Not Cross An ABR
◙ Type 3 – Summary LSAS: – Advertised By The ABR Of The Originating Area
◙ Type 4 – Summary LSAS: – Used To Advertise A Metric To The ASBR And Advertised By The ABR Of The Originating Area
◙ Type 5 – As External LSAS: – Used To Advertise Network From Other Autonomous Systems And Is Advertised And Owned By The Originating ASBR (Need Type 4 To Find The ASBR)
◙ Type 6: – Multicast OSPF LSAS
◙ Type 7 – LSAS Defined For Not-So-Stubby Areas (NSSA): – Used To Advertise Networks From Other Autonomous Systems Injected Into An NSSA Area And Is Advertised And Owned By The Originating ASBR. Translated To Type 5 By The NSSA ABR
◙ Type 8 – External Attribute LSAS For BGP
◙ Types 9, 10 & 11: – Opaque LSAS
TYPES OF OSPF ROUTES
◙ OSPF Intra-Area Routes (Router LSA And Network LSA)
✓ IA – OSPF Interarea Routes (Summary LSA) ✓ E1 – OSPF Type 1 External Routes (Advertised By External LSA)
◙ E2 – OSPF Type 2 External Routes (Advertised By External LSA) – This Is The Default For Redistributed Routes
◙ E1 – External Routes Calculate The Cost By Adding The External Cost To The Internal Cost Of Each Link That The Packet Crosses
◙ E2 – The External Cost Of O E2 Packets Routes Is Always The External Cost Only
OSPF PASSIVE INTERFACE
◙ The Sending And Receiving Of Routing Updates Is Disabled
◙ The Specified Interface Address Appears As A Stub Network In The OSPF Domain
DESIGN LIMITATIONS OF OSPF:
◙ If More Than One Area Is Configured, One Must Be Area 0, The Backbone Area
◙ All Areas Must Be Connected To Area 0
◙ Area 0 Must Be Contiguous
VIRTUAL LINKS
◙ An Extension Of The Backbone
◙ Carried By Nonbackbone Area
◙ Cannot Be Created Across A Stub Or NSSA Area
◙ Used To Allow Areas To Connect To Areas Other Than Area 0
◙ Used To Repair A Discontiguous Area 0
AREA TYPES:
◙ Backbone Area – Connects All Other Areas
◙ Normal Area – Contains All Internal And External Routing Information
◙ Stub Area – Contains Internal And Area Routing Information, But Not External Routing Information
◙ Totally Stubby Area – Contains Area Routing Information Only. Cisco Proprietary
◙ NSSA – Contains Area And External Routing Information
OSPF AUTHENTICATION:
◙ Simple Password Authentication
◙ MD5 Authentication
◙ Router Generates And Checks Every OSPF Packet
◙ The Source Of Each Routing Update Packet Received Is Authenticated
◙ Each Participating Neighbor Must Have The Same Key (Password) Configured.
FOR OSPF MORE REFERENCE:
1. ◙ - ➤ OSPF Vs EIGRP, BGP And RIP:
2. ◙ - ➤ OSPF Short Notes:
3. ◙ - ➤ Just Recap About OSPF:
4. ◙ - ➤ OSPF Quick Reference:
5. ◙ - ➤ OSPF Quick Reference Table:
6. ◙ - ➤ OSPFv2 (IPv4) Vs OSPFv3 (IPv6):
7. ◙ - ➤ OSPF Review Questions And Answers:
8. ◙ - ➤ OSPF LSA Types And LSA Operation:
9. ◙ - ➤ OSPF Configuration Examples:
10. ◙ - ➤ OSPF MD5 Authentication:
11. ◙ - ➤ Redistribution OSPF With BGP And EIGR:
OSPF QUEST
Answer: From The Perspective Of An OSPF Router, A Neighbor Is Another OSPF Router That Is Attached To One Of The First Router's Directly Connected Links.
115. WHAT IS AN OSPF ADJACENCY?
Answer: An OSPF Adjacency Is A Conceptual Link To A Neighbor Over Which LSAs Can Be Sent.
116. WHAT ARE THE FIVE OSPF PACKET TYPES? WHAT IS THE PURPOSE OF EACH TYPE?
Answer:
OSPF Packet Types, As OSPF Link-State Information Is Shared Between Areas, An Intricate Set Of Mechanisms Is Followed, Relying On A Number Of Different OSPF Packet Types. All OSPF Traffic Is Transmitted Inside IP Packets. Receivers Recognize OSPF Traffic Because It Is Marked As IP Protocol 89.
OSPF PACKET TYPES AND THEIR PURPOSES:
✓ Hello packets — Establish Communication With Directly Attached Neighbors.
✓ Database Descriptor (DBD) — Sends A List Of Router Ids From Whom The Router Has An LSA And The Current Sequence Number. This Information Is Used To Compare Information About The Network.
✓ Link State Requests (LSR) — Follow DBDs To Ask For Any Missing LSAs.
✓ Link State Update (LSU) — Replies To A Link-State Request With The Requested Data.
✓ Link-State Acknowledgements (LSACK) — Confirm Receipt Of Link-State Information.
117: WHAT IS AN LSA? HOW DOES AN LSA DIFFER FROM AN OSPF UPDATE PACKET?
Answer: A Router Originates A Link State Advertisement To Describe One Or More Destinations.
An OSPF Update Packet Transports LSAs From One Neighbor To Another. Although LSAs Are Flooded Throughout An Area Or OSPF Domain, Update Packets Never Leave A Data Link.
118. WHAT ARE LSA TYPES 1 TO 5 AND LSA TYPE 7? WHAT IS THE PURPOSE OF EACH TYPE?
Answer:
THE MOST COMMON LSA TYPES AND THEIR PURPOSES ARE:
✓ Type 1 (Router LSAs) Are Originated By Every Router And Describe The Originating Router, The Router's Directly Connected Links And Their States, And The Router \ XD5 S Neighbors.
✓ Type 2 (Network LSAs) Are Originated By Designated Routers On Multiaccess Links And Describe The Link And All Attached Neighbors.
✓ Type 3 (Network Summary LSAs) Are Originated By Area Border Routers And Describe Inter-Area Destinations.
✓ Type 4 LSAs (ASBR Summary LSAs) Are Originated By Area Border Routers To Describe Autonomous System Boundary Routers Outside The Area.
✓ Type 5 (AS External LSAs) Are Originated By Autonomous System Boundary Routers To Describe Destinations External To The OSPF Domain.
✓ Type 7 (NSSA External LSAs) Are Originated By Autonomous System Boundary Routers Within Not-So-Stubby Areas.
119. WHAT IS A LINK STATE DATABASE? WHAT IS LINK STATE DATABASE SYNCHRONIZATION?
Answer:
The Link State Database Is Where A Router Stores All The OSPF LSAs It Knows Of, Including Its Own.
Database Synchronization Is The Process Of Ensuring That All Routers Within An Area Have Identical Link State Databases.
120. WHAT IS THE DEFAULT HELLO INTERVAL?
Answer: The Default OSPF Hello Interval Is 10 Seconds.
121. WHAT IS THE DEFAULT ROUTER DEAD INTERVAL?
Answer: The Default Router Dead Interval Is Four Times The Hello Interval.
122. WHAT IS A ROUTER ID? HOW IS A ROUTER ID DETERMINED?
Answer: A Router ID Is An Address By Which An OSPF Router Identifies Itself. It Is Either The Numerically Highest IP Address Of All The Router's Loopback Interfaces, Or If No Loopback Interfaces Are Configured, It Is The Numerically Highest IP Address Of All The Router's LAN Interfaces.
123. WHAT IS AN AREA?
Answer: An Area Is An OSPF Sub-Domain, Within Which All Routers Have An Identical Link State Database.
124. WHAT IS THE SIGNIFICANCE OF AREA 0?
Answer: Area 0 Is The Backbone Area. All Other Areas Must Send Their Inter-Area Traffic Through The Backbone.
125. WHAT IS MAXAGE?
Answer: Maxage, 1 Hour, Is The Age At Which An LSA Is Considered To Be Obsolete.
126. WHAT ARE THE FOUR OSPF ROUTER TYPES?
Answer:
◙ - ➤ Internal Routers, Whose OSPF Interfaces All Belong To The Same Area
◙ - ➤ Backbone Routers, Which Are Internal Routers In Area 0 Area
◙ - ➤ Border Routers, Which Have OSPF Interfaces In More Than One Area Autonomous System Boundary Routers, Which Advertise External Routes Into The OSPF Domain.
127. WHAT ARE THE FOUR OSPF PATH TYPES?
Answer:
✓ Intra-Area Paths
✓ Inter-Area Paths
✓ Type 1 External Paths
✓ Type 2 External Paths
128. WHAT ARE THE FIVE OSPF NETWORK TYPES?
Answer:
✓ Point-To-Point Networks
✓ Broadcast Networks
✓ Non-Broadcast Multi-Access (NBMA) Networks
✓ Point-To-Multipoint Networks
✓ Virtual Links
129. WHAT IS A DESIGNATED ROUTER?
Answer: A Designated Router Is A Router That Represents A Multiaccess Network, And The Routers Connected To The Network, To The Rest Of The OSFP Domain.
130. HOW DOES A CISCO ROUTER CALCULATE THE OUTGOING COST OF AN INTERFACE?
Answer: Cisco IOS Calculates The Outgoing Cost Of An Interface As 108/BW, Where BW Is The Configured Bandwidth Of The Interface.
131. WHAT IS A PARTITIONED AREA?
Answer: An Area Is Partitioned If One Or More Of Its Routers Cannot Send A Packet To The Area's Other Routers Without Sending The Packet Out Of The Area.
132. WHAT IS A VIRTUAL LINK?
Answer: A Virtual Link Is A Tunnel That Extends An OSPF Backbone Connection Through A Non-Backbone Area.
133. WHAT IS THE DIFFERENCE BETWEEN A STUB AREA, A TOTALLY STUBBY AREA, AND A NOT-SO-STUBBY AREA?
Answer:
✓ A Stub Area Is An Area Into Which No Type 5 LSAs Are Flooded.
✓ A Totally Stubby Area Is An Area Into Which No Type 3, 4, Or 5 LSAs Are Flooded, With The Exception Of Type 3 Lsas To Advertise A Default Route.
✓ Not-So-Stubby Areas Are Areas Through Which External Destinations Are Advertised Into The OSPF Domain, But Into Which No Type 5 Lsas Are Sent By The ABR.
134. WHAT IS THE DIFFERENCE BETWEEN OSPF NETWORK ENTRIES AND OSPF ROUTER ENTRIES?
Answer: OSPF Network Entries Are Entries In The Route Table, Describing IP Destinations. OSPF Router Entries Are Entries In A Separate Route Table That Record Only Routes To ABRs And ASBRs.
135. WHY IS TYPE 2 AUTHENTICATION PREFERABLE OVER TYPE 1 AUTHENTICATION?
Answer: Type 2 Authentication Uses MD5 Encryption, Where As Type 1 Authentication Uses Clear-Text Passwords.
136. WHICH THREE FIELDS IN THE LSA HEADER DISTINGUISH DIFFERENT LSAS? WHICH THREE FIELDS IN THE LSA HEADER DISTINGUISH DIFFERENT INSTANCES OF THE SAME LSA?
Answer: The Three Fields In The LSA Header That Distinguish Different LSAs Are The Type, Advertising Router, And The Link State ID Fields. The Three Fields In The LSA Header That Distinguish Different Instances Of The Same LSA Are The Sequence Number, Age, And Checksum Fields.
BGP REFERENCES
1 ◙ - ➤ BGP Quick References:
2 ◙ - ➤ BGP Neighbors Concepts:
3 ◙ - ➤ BGP Lab Virtual Link:
4 ◙ - ➤ BGP Lab For Route Reflectors Client:
5 ◙ - ➤ BGP Lab Redistribute Versus OSPF:
6 ◙ - ➤ Redistribution BGP Vs OSPF And EIGRP:
7 ◙ - ➤ BGP MD5 Authentication:
8. ◙ - ➤ just Recap References About BGP With Questions And Answers:
IS-IS
IS-IS Is A Routing Protocol Designed To Move Information Efficiently Within A Computer Network, A Group Of Physically Connected Computers Or Similar Devices. It Accomplishes This By Determining The Best Route For Datagrams Through A Packet-Switched Network. The Protocol Was Defined In ISO/IEC 10589:2002 As An International Standard Within The Open Systems Interconnection (OSI) Reference Design. Though Originally An ISO Standard, The IETF Republished The Protocol As An Internet Standard In RFC 1142 . IS-IS Has Been Called "The De Facto Standard For Large Service Provider Network Backbones
137. WHAT IS AN INTERMEDIATE SYSTEM?
Answer: An Intermediate System Is The ISO Term For A Router.
138. WHAT IS A NETWORK PROTOCOL DATA UNIT?
Answer: A Network Protocol Data Unit Is The ISO Term For A Packet.
139. WHAT IS THE DIFFERENCE BETWEEN AN L1, AN L2, AND AN L1/L2 ROUTER?
Answer:
✓ An L1 Router Has No Direct Connections To Another Area. An L2 Router Only Routes Inter-Area Traffic.
✓ An L1/L2 Router Routes Both Inter-Area And Intra-Area Traffic And Acts As An Inter-Area Gateway For L1 Routers.
140. EXPLAIN THE BASIC DIFFERENCE BETWEEN AN IS-IS AREA AND AN OSPF AREA.
Answer: The Borders Of IS-IS Areas Are Between Routers, On Links. The Borders Of OSPF Areas Are Defined By The Routers Themselves.
141. WHAT IS A NETWORK ENTITY TITLE (NET)?
Answer: The Network Entity Title Is An Address By Which A Router Identifies Both Itself And The Area In Which It Resides.
142. TO WHAT VALUE MUST THE NSAP SELECTOR BE SET IN A NET?
Answer: The NSAP Selector Should Be Set To 0x00 In A NET.
143. WHAT IS THE PURPOSE OF A SYSTEM ID?
Answer: The System ID Uniquely Identifies A Router Within An IS-IS Domain.
144. HOW DOES A ROUTER DETERMINE WHAT AREA IT IS IN?
Answer: The Portion Of The NET Preceding The Last Seven Octets Is The Area Address.
145. DOES IS-IS ELECT A BACKUP DESIGNATED ROUTER ON A BROADCAST SUBNETWORK?
Answer: IS-IS Does Not Elect A BDR.
146. WHAT IS THE PURPOSE OF THE PSEUDONODE ID?
Answer: The PSEUDONODE ID Is The Last Octet Of A LAN ID. Its Purpose Is To Distinguish LAN IDs Which Are Originated By A Single Router Which Is The DR On Multiple LANs.
147. WHAT IS THE MAXIMUM AGE (MAXAGE) OF AN IS-IS LSP?
Answer: The Maxage Of An IS-IS LSP Is 1200 Seconds (20 Minutes).
148. WHAT IS THE BASIC DIFFERENCE BETWEEN THE WAY OSPF AGES ITS LSAS AND THE WAY IS-IS AGES ITS LSPS?
Answer: OSPF Increments The Age Up To Maxage; IS-IS Decrements The Age Down To 0. A New OSPF LSA Has An Age Of 0, Whereas A New IS-IS LSP Has An Age Of Maxage.
149. HOW OFTEN DOES AN IS-IS ROUTER REFRESH ITS LSPS?
Answer: The Refresh Rate Of An IS-IS Router Is 900 Seconds (15 Minutes).
150. WHAT IS A COMPLETE SEQUENCE NUMBER PACKET (CSNP)? HOW IS IT USED?
Answer: A Complete Sequence Number Packet Contains A Full Listing Of All Lsps In A Database. A CSNP Is Periodically Sent By The Designated Router On A Broadcast Network To Maintain Database Synchronization.
151. WHAT IS A PARTIAL SEQUENCE NUMBER PACKET (PSNP)? HOW IS IT USED?
Answer: A Partial Sequence Number Packet Contains A Listing Of One Or More LSPs. It Has Two Uses: On Point-To-Point Networks, It Is Used To Acknowledge The Receipt Of LSPs. On Broadcast Networks, It Is Used To Request LSPs.
152. WHAT IS THE PURPOSE OF THE OVERLOAD (OL) BIT?
Answer: An IS-IS Router Uses The Overload Bit To Inform Its Neighbors That It Is Experiencing A Memory Overload And Cannot Store The Entire Link State Database.
153. WHAT IS THE PURPOSE OF THE ATTACHED (ATT) BIT?
Answer: The Attached Bit Is Used By L1/L2 Routers To Inform L1 Routers That It Is Attached To The L2 Backbone.
154. WHAT METRICS ARE SPECIFIED BY THE ISO FOR IS-IS? HOW MANY OF THESE METRICS DOES THE CISCO IOS SUPPORT?
Answer: The ISO Specifies Four Metrics: Default, Expense, Delay, And Error. Cisco Supports Only The Default Metric.
155. WHAT IS THE MAXIMUM VALUE OF THE IS-IS DEFAULT METRIC?
Answer: The Maximum Value Of Any Of The IS-IS Metrics Is 63.
156. WHAT IS THE MAXIMUM METRIC VALUE OF AN IS-IS ROUTE?
Answer: The Maximum Metric Value Of An IS-IS Route Is 1023.
157. WHAT IS THE DIFFERENCE BETWEEN A LEVEL 1 IS-IS METRIC AND A LEVEL 2 IS-IS METRIC?
Answer: L1 IS-IS Metrics Apply To Intra-Area Routes, And L2 IS-IS Metrics Apply To Inter-Area Routes.
158. WHAT IS THE DIFFERENCE BETWEEN AN INTERNAL IS-IS METRIC AND AN EXTERNAL IS-IS METRIC?
Answer: Internal Metrics Apply To Routes To Destinations Within The IS-IS Domain. External Metrics Apply To Routes To Destinations External To The IS-IS Domain.
CONCLUSION:
The Goal Of This Article Is To Give An Easy Way To Understand The “QUICK REFERENCE - REVIEW QUESTIONS AND ANSWERS (IP ROUTING, RIP, IGP, EIGRP, OSPF, BGP,IS-IS)" And Also We Hope This Guide Will Help Every Beginner Who Are Going To Start Cisco Lab Practice Without Any Doubts. Some Topics That You Might Want To Pursue On Your Own That We Did Not Cover In This Article Are Listed Here!Hands - On Experience Is An Invaluable Part Of Preparing For The Lab Exam And Never Pass Up An Opportunity To Configure Or Troubleshoot A Router ( If You Have Access To Lab Facilities, Take Full Advantage Of Them) There Is No Replacement For The Experience You Can Gain From Working In A Lab, Where You Can Configure Whatever You Want To Configure And Introduce Whatever Problems You Want To Introduce, Without Risk Of Disrupting A Production Network. Thank You And Best Of Luck
This Article Written Author By: Premakumar Thevathasan - CCNA, CCNP, MCSE, MCSA, MCSA - MSG, CIW Security Analyst, CompTIA Certified A+ And Etc.
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