COMPONENTS USED:
The Ability To Configure A Static Route Was Introduced In Cisco IOS® Software Release 10.0. Static Routes Are Used For A Variety Of Reasons And Are Often Used When There Is No Dynamic Route To The Destination, Or When You Run A Dynamic Routing Protocol Is Not Feasible.
BEFOREWE BEGIN:
TO SUBJECT YOU’LL SIMPLEY KNOW WHAT IS ROUTER & HOST?
HOST (END-SYSTEM):
ROUTER:
WHAT DOES A ROUTER DO?
OVERVIEW:
WHAT IS ROUTING:
Routing Is The Process That A Router Uses To Forward Packets Toward The Destination Network. Is The Act Of Moving Information Across An Internetwork From A Source To A Destination.
Router Makes Decisions Based Upon The Destination IP Address Of A Packet. All Devices Along The Way Use The Destination IP Address To Send The Packet In The Right Direction To Reach Its Destination. To Make The Correct Decisions, Routers Must Learn How To Reach Remote Networks. When Routers Use Dynamic Routing, This Information Is Learned From Other Routers. When Static Routing Is Used, Network Administrator Configures Information About Remote Networks Manually.
ROUTING COMPONENTS
Routing Involves Two Basic Activities: Determining Optimal Routing Paths And Transporting Information Groups (Typically Called Packets) Through An Internetwork. In The Context Of The Routing Process, The Latter Of These Is Referred To As Switching. Although Switching Is Relatively Straightforward, Path Determination Can Be Very Complex.
PATH DETERMINATION:
A Metric Is A Standard Of Measurement, Such As Path Length, That Is Used By Routing Algorithms To Determine The Optimal Path To A Destination. To Aid The Process Of Path Determination, Routing Algorithms Initialize And Maintain Routing Tables, Which Contain Route Information. Route Information Varies Depending On The Routing Algorithm Used.
Routing Algorithms Fill Routing Tables With A Variety Of Information. Destination/Next Hop Associations Tell A Router That A Particular Destination Can Be Gained Optimally By Sending The Packet To A Particular Router Representing The "Next Hop" On The Way To The Final Destination. When A Router Receives An Incoming Packet, It Checks The Destination Address And Attempts To Associate This Address With A Next Hop.
The Routing Process Usually Directs Forwarding On The Basis Of Routing Tables Which Maintain A Record Of The Routes To Various Network Destinations. Thus, Constructing Routing Tables, Which Are Held In The Router's Memory, Is Very Important For Efficient Routing. Most Routing Algorithms Use Only One-Network Path At A Time, But Multipath Routing Techniques Enable The Use Of Multiple Alternative Paths.
For Routing Between Routers To Work Efficiently In An Internet Work, Routers Must Have Knowledge Of Other Network Ids Or Be Configured With A Default Route. On Large Internet Works, The Routing Tables Must Be Maintained So That The Traffic Always Travels Along Optimal Paths.
(A Default Route That Is Used When No Other Routes For The Destination Are Found In The Routing Table. That Are Used To Establish A Gateway Of Last Resort For Your Router. Its is Used To Send Packets With A Remote Destination Network Not In The Routing Table To The Next-Hop Router. You Should Only Use Default Routing On Stub Networks—Those With Only One Exit Path Out Of The Network. ).
How The Routing Tables Are Maintained Defines The Distinction Between STATIC AND DYNAMIC ROUTING. The Most Routing Can Be Classified As Either Static Or Dynamic.
INTRODUCTION OF STATIC VS DYNAMIC:
THERE ARE MOST TWO WAYS OF ROUTING THAT CAN BE CONFIGURED ON A NETWORK DEVICE:
There Are Various Routing Algorithms And Depending On These Routing Algorithms, The Information Stored In The Routing Table Varies. Every Router Has Its Own Routing Table And It Fills This Table With The Required Information To Calculate The Optimal Path Between The Source Router And The Destination Router.
(Also Know What Is Routing Algorithm? It Is Defines The System For Sending And Receiving Routing Details. It Also Defines The System For Calculating The Very Best Path And Adding Routes Within The Routing Table. Last But Not Least, It Defines The System For Detecting To Topology Adjustments.
There Are Two Main Routing Algorithms Or Better Regarded As Routing Protocols That You Just Ought To Understand, Are Distance Vector And Link-State).
Before Understand The STATIC Versus DYNAMIC Routing, First We Know What Is ROUTING TABLES.
UNDERSTAND THE ROUTING TABLE:
During The Routing Process, The Routing Decisions Of Hosts And Routers Are Aided By A Database Of Routes Known As The Routing Table.
The Routing Table Is Used To Store All The Routes From All Possible Sources. The Routing Table Is Not Exclusive To A Router. Depending On The Routable Protocol, Hosts May Also Have A Routing Table That May Be Used To Decide The Best Router For The Packet To Be Forwarded. IP Hosts Have A Routing Table. IPX Hosts Do Not Have A Routing Table.
Is A Database Which Keeps Track Of Paths, Like A Map, And Allows The Gateway To Provide This Information To The Node Requesting The Information. With Hop-By-Hop Routing, Each Routing Table Lists, For All Reachable Destinations, The Address Of The Next Device Along The Path To That Destination The Next Hop. Assuming That The Routing Tables Are Consistent, The Simple Algorithm Of Relaying Packets To Their Destination's Next Hop Thus Suffices To Deliver Data Anywhere In A Network.
That Is Used To Determine Where Data Packets Traveling Over An Internet Protocol (IP) Network Will Be Directed. All IP-Enabled Devices, Including Routers And Switches, Use Routing Tables. When A Packet Is Received, A Network Device Examines The Packet And Matches It To The Routing Table En The Best Match For Its Destination. The Table Then Provides The Device With Instructions For Sending The Packet To The Next Hop On Its Route Across The Network.
THERE ARE THREE PROCESSES INVOLVED IN BUILDING AND MAINTAINING THE ROUTING TABLE IN A CISCO ROUTER:
A BASIC ROUTING TABLE INCLUDES THE FOLLOWING INFORMATION:
COMMAN ROUTING TABLE STRUCTURE:
Entries In The Routing Table Usually Consist Of The Following Fields:NETWORK ID: The Network ID Field Contains The Identification Number For A Network Route Or An Internetwork Address For A Host Route.
FORWARDING ADDRESS: The Forwarding Address Field Contains The Address To Which The Packet Is To Be Forwarded. The Forwarding Address Can Be A Network Interface Card Address Or An Internet Work Address. For Network Ids To Which The End System Or Router Is Directly Attached, The Forwarding Address Field May Be Blank.
INTERFACE: METRIC: The Metric Field Indicates The Cost Of A Route. If Multiple Routes Exist To A Given Destination Network ID, The Metric Is Used To Decide Which Route Is To Be Taken. The Route With The Lowest Metric Is The Preferred Route. Some Routing Algorithms Only Store A Single Route To Any Network ID In The Routing Table Even When Multiple Routes Exist. In This Case, The Metric Is Used By The Router To Decide Which Route To Store In The Routing Table.
METRICS CAN INDICATE DIFFERENT WAYS OF EXPRESSING A ROUTE PREFERENCE:
HOP COUNT: A Common Metric. Indicates The Number Of Routers (Hops) In The Path To The Network ID.
DELAY:A Measure Of Time That Is Required For The Packet To Reach The Network ID. Delay Is Used To Indicate The Speed Of The Path—Local Area Networks (LAN) Links Have A Low Delay, Wide Area Network (WAN) Links Have A High Delay—Or A Congested Condition Of A Path.
THROUGHPUT: The Effective Amount Of Data That Can Be Sent Along The Path Per Second. Throughput Is Not Necessarily A Reflection Of The Bit Rate Of The Link, As A Very Busy Ethernet Link May Have A Lower Throughput Than An Unutilized 64-Kbps WAN Link.
RELIABILITY: A Measure Of The Path Constancy. Some Types Of Links Are More Prone To Link Failures Than Others. For Example, With WAN Links, Leased Lines Are More Reliable Than Dial-Up Lines.
LIFETIME: The Lifetime Field Indicates The Lifetime That The Route Is Considered Valid. When Routes Are Learned Through The Exchange Of Information With Other Routers, This Is An Additional Field That Is Used. Learned Routes Have A Finite Lifetime. To Keep A Learned Route In The Routing Table, The Route Must Be Refreshed Through A Periodic Process. If A Learned Route's Lifetime Expires, It Is Removed From The Routing Table. The Timing Out Of Learned Routes Provides A Way For Routers To Reconfigure Themselves When The Topology Of An Internet work Changes Due To A Downed Link Or A Downed Router.
ROUTING TABLES CAN BE MAINTAINED MANUALLY OR DYNAMICALLY.
Dynamic Routing Tables Allow Devices To "Listen" To The Network And Respond To Occurrences Like Device Failures And Network Congestion.
HOW ROUTING TABLES WORK?
STATIC ROUTING USES: A Routing Table That Has Been Reconfigured Manually. All Entries Will Remain The Same Unless They Are Changed Manually. This Works Fine If All Machines Remain On The Same Subnet And Always Have The Same IP Address (And Assuming All Routers Remain Functional). Unfortunately, This Ideal Set Of Circumstances Doesn’t Always Apply.
DYNAMIC ROUTING PROTOCOLS ALLOW ROUTERS: To Get Information From Other (Peer) Routers On The Network In Order To Update Routing Table Entries Without Human Intervention.
Whichever Way The Table Is Built, When A Router Or Host Computer On Which IP Forwarding Is Enabled Sends An IP Datagram, It Must Determine Which Physical Interface Address To Use. (Remember That It Is Connected To At Least Two Networks, With A Separate Interface To Each Network.) If The Packet Is Destined For An Address On A Subnet To Which It Is Not Connected, It Will Use The Routing Table To Determine That The Packet Should Be Sent To A Gateway.
The Routing Table Contains The (Logical) IP Address Of The Gateway. The Address Resolution Protocol (ARP) Will Then Use The IP Address To Determine The Physical (MAC) Address Of The Gateway. The Datagram Will Be Forwarded From Router To Router Until It Eventually Reaches The Router That Is Connected To The Destination Subnet Or Host.
The Data Entered In The Routing Table Is Referred To When The Best Possible Path To Transfer Information Across Two Computers In A Network Is To Be Determined.
THE TWO CLASSIFICATIONS:Static And Dynamic Routing, Are Based On The Way In Which The Routing Tables Are Updated Every Time They Are Used.
Let Us Compare The Two Types Of Routing Algorithms Based On The Static And Dynamic Routing Algorithm Used,
IN THE STATIC VS. DYNAMIC ROUTING SECTION GIVEN BELOW.
FIRST GO WE FOR STATIC ROUTES:
The Ability To Configure A Static Route Was Introduced In Cisco IOS® Software Release 10.0. Static Routes Are Used For A Variety Of Reasons And Are Often Used When There Is No Dynamic Route To The Destination, Or When You Run A Dynamic Routing Protocol Is Not Feasible.
Static Routing Algorithms Are Basically Table Mappings Established By The Network Administrator Before The Beginning Of Routing. These Mappings Do Not Change Unless The Network Administrator Alters Them. Algorithms That Use Static Routes Are Simple To Design And Work Well In Environments Where Network Traffic Is Relatively Predictable And Where Network Design Is Relatively Simple. Because Of This Fact, Static Routing Systems Cannot React To Network Changes.
The Information About The Networks That Are Directly Connected To The Active Router Interfaces Are Added To The Routing Table Initially And They Are Known As Connected Routes. In Static Routing, The Network Administrator Sets Up “Turn By Turn” Directions For How Traffic Gets From One Subnet To Another, And From Those Subnets To Other Networks Such As The Internet. For Each Destination Network Or Subnet, The Administrator Adds A Static Route That Specifies The Next Router On That Network That Should Receive The Packet, In Order For It To Get To Its Final Destination. In These Systems, Routes Through A Data Network Are Described By Fixed Paths (Statically).
Static Routes Remain In The Routing Table Even If The Specified Gateway Becomes Unavailable. If The Specified Gateway Becomes Unavailable, You Need To Remove The Static Route From The Routing Table Manually. However, Static Routes Are Removed From The Routing Table If The Specified Interface Goes Down, And Are Reinstated When The Interface Comes Back Up.
An Entire Network Can Be Configured Using Static Routes, But This Type Of Configuration Is Not Fault Tolerant. When There Is A Change In The Network Or A Failure Occurs Between Two Statically Defined Nodes, Traffic Will Not Be Rerouted. This Means That Anything That Wishes To Take An Affected Path Will Either Have To Wait For The Failure To Be Repaired Or The Static Route To Be Updated By The Administrator Before Restarting Its Journey.
NOTE: Although Static Routing Is Not An Ideal Total Solution For IP Route Announcement In Large Networks, It Is A Very Effective Solution For Small (Single Gateway) Networks And Provides Needed Gateway And Route Redirection Services. Static Routes Are Also Essential To Announcing Networks Where The Access Links Are Unstable Or Temporary (As With Dial-Up Connections).
Static Routes Are Set In The Cisco IOS Using The “ IP Route ”Configuration EXEC Command.
Most Requests Will Time Out (Ultimately Failing) Before These Repairs Can Be Made. There Are, However, Times When Static Routes Can Improve The Performance Of A Network. Some Of These Include Stub Networks And Default Routes.
THE BENEFITS OF STATIC ROUTES:
Static Routing Has Some Enormous Advantages Over Dynamic Routing. Chief Among These Advantages Is Predictability. Because The Network Administrator Computes The Routing Table In Advance, The Path A Packet Takes Between Two Destinations Is Always Known Precisely, And Can Be Controlled Exactly. With Dynamic Routing, The Path Taken Depends On Which Devices And Links Are Functioning, And How The Routers Have Interpreted The Updates From Other Routers.
Additionally, Because No Dynamic Routing Protocol Is Needed, Static Routing Doesn't Impose Any Overhead On The Routers Or The Network Links. While This Overhead May Be Minimal On An FDDI Ring, Or Even On An Ethernet Segment, It Could Be A Significant Portion Of Network Bandwidth On A Low-Speed Dial-Up Link. Consider A Network With 200 Network Segments. Every 30 Seconds, As Required By The RIP Specification, The Routers All Send An Update Containing Reachability Information For All 200 Of These Segments. With Each Route Taking 16 Octets Of Space, Plus A Small Amount Of Overhead, The Minimum Size For An Update In This Network Is Over Three Kilobytes. Each Router Must Therefore Send A 3 Kb Update On Each Of Its Interfaces Every 30 Seconds. As You Can See, For A Large Network, The Bandwidth Devoted To Routing Updates Can Add Up Quickly.
Finally, Static Routing Is Easy To Configure On A Small Network. The Network Administrator Simply Tells Each Router How To Reach Every Network Segment To Which It Is Not Directly Attached.
SOME DISADVANTAGES TO STATIC ROUTES:
STATIC ROUTE OPERATIONS CAN BE DIVIDED INTO THESE THREE PARTS:
An Administrator Must Use The IP Route Command To Manually Configure A Static Route.
FOR EXAMPLE:
Router(Config)# IP Route
Router>Enable
Router# Con T
Router(config)#IP Route 172.16.3.0 255.255.255.0 172.16.4.1 130
If The Router Cannot Reach The Outgoing Interface That Is Being Used In A Route, The Route Will Not Be Installed In The Routing Table. This Means If That Interface Is Down, The Route Will Not Be Placed In The Routing Table.
< b>Sometimes Static Routes Are Used For Backup Purposes. A Static Route Can Be Configured On A Router That Will Only Be Used When The Dynamically Learned Route Has Failed. To Use A Static Route As A Backup, Set A Higher Administrative Distance Than The Dynamic Routing Protocol.
ALSO STATIC ROUTES ARE USED FOR A COUPLE OF REASONS:
ALSO USING STATIC ROUTES ALONG SIDE DYNAMIC ROUTES:
Choosing To Use Static Routes In Your Network Configuration Should Be An Either Or Choice. You Don’t Have To Use Only Static Routes, And You Don’t Have To Use Only Dynamic Routes. Because The Cisco IOS Uses Administrative Distances You Can Actually Use Static Routes Right Along Side Dynamic Routes And Whichever Route Has The Lowest Administrative Distance Will Get Used First.
ROUTE SELECTION:
The Router Will Use All The Available Sources Of Reachability Information To Construct The Most Accurate And Efficient Routing Table Possible, Based On The Available Information. Each Information Source Is Assigned An Administrative Distance, Which Is Used To Determine A Route’s Integrity.
ADMINISTRATIVE DISTANCE:
Also Know What Is Administrative Distance Is An Optional Parameter That Indicates The Reliability Of A Route. Administrative Distance Is The Measure Used By Cisco Routers To Select The Best Path When There Are Two Or More Different Routes To The Same Destination From Two Different Routing Protocols.
If We Say Another Way Administrative Distance Is The Feature That Routers Use In Order To Select The Best Path When There Are 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 Is Prioritized In Order Of Most To Least Reliable (Believable) With The Help Of An Administrative Distance Value.
The Lower The Administrative Distance Value, The More Trusted The Route. So, You Can See In Situations Where Multiple Routing Protocols Are Being Used For Route Advertisement, The Router Will Prefer Information Provided From Certain Protocols Over Others.
One Of The Big Advantages Of Employing This Advertisement Hierarchy Is That It Gives You Another Way To Manage Traffic Flow In Dynamic Routing. By Using Static Routes (Which Have A Lower Administrative Distance Than Any Dynamic Protocol), You Can Overrule Dynamic Announcements In Multipath Networks To Specify The Route Path To Specific Hosts. By The Same Token, It Is Possible To Set A Static Route To Use A Higher Administrative Distance So A Dynamic Route Is Preferred And The Static Route Is Only Used In The Event That Dynamic Route Announcement Is Lost.
Static Routes By Default Have An Administrative Distance Of 1. Routes Have Are Directly Connected Have An Administrative Distance Of 0. The Default Administrative Distance When Using A Static Route Is 1. In The Routing Table, It Will Show The Static Route With The Outgoing Interface Option As Being Directly Connected. This Is Sometimes Confusing, Since A True Directly Connected Route Has An Administrative Distance Of 0.
When There Are Two Or More Routes To The Same Destination, Routers Use Administrative Distance To Decide Which Routing Protocol (Or Static Route) To Trust More.
For Example: Here Are Some Administrative Distances (The Lower The Number, The More Trustworthy The Type Of Route Is): Static Route To A Connected Interface = 0 - Static Route To A Ip Address = 1 - Internal EIGRP = 90 - OSPF = 110 - RIP = 120
Because Of How Administrative Distance Works, When You Enter Static Routes That Are The Same As A Dynamic Route (Learned From Another Router), Your Static Route Will Be Used Over The Dynamic Route. As You May Be Overriding Routes Manually, You Must Make Sure Your Routes Are Accurate.
As You May Have Noticed Above, There Are Static Routes That Point To An Interface On The Router, And Static Routes That Point To An Ip Address On The Network.
How To Verify The Administrative Distance Of A Particular Route, Use The ”Show IP Route“Address Command, Where The IP Address Of The Particular Route Is Inserted For The Address Option. If An Administrative Distance Other Than The Default Is Desired, A Value Between 0 And 255 Is Entered After The Next-Hop Or Outgoing Interface As Follows:
WHY WE NEAD ADMINISTRATIVE DISTANCE:
Most Routing Protocols Have Metric Structures And Algorithms That Are Not Compatible With Other Protocols. In A Network With Multiple Routing Protocols, The Exchange Of Route Information And The Capability To Select The Best Path Across The Multiple Protocols Are Critical.
CONFIGURING STATIC ROUTES:
USE THE FOLLOWING STEPS (Step By Step Command Syntax For Static Route):
STEP 1: Determine All Desired Prefixes, Masks, And Addresses. The Address Can Be Either A Local Interface Or A Next Hop Address That Leads To The Desired Destination.
STEP 2: Enter Global Configuration Mode.
STEP 3: Type The IP Route Command With A Prefix And Mask Followed By The Corresponding Address From Step 1. The Administrative Distance Is Optional.
STEP 4: Repeat Step 3 For All The Destination Networks That Were Defined In Step 1.
STEP 5: Exit Global Configuration Mode.
STEP 6: Use The “Copy Running-Config Startup-Config” Command To Save The Active Configuration To NVRAM.
Router(Config)# IP Route
EXAMPLE – 1: FOR STATIC ROUTES:
To Configure A Static Route To Network 10.10.20.0/24, Pointing To A Next-Hop Router With The IP Address Of 192.168.100.1
Router> Enable
Router# Configure Terminal
Router(Config)# Ip Route 10.10.20.0 255.255.255.0 192.168.100.1
The Other Option Is To Define A Static Route With Reference To The Outgoing Interface Which Is Connected To The Next Hop Towards The Destination Network.
Router> Enable
Router# Configure Terminal
Router(Config)# IP Route 10.10.20.0 255.255.255.0 Serial 0/0
EXAMPLE – 2:
Router(Config)#Ip Route 172.16.1.0 255.255.255.0 172.16.2.1 5
Static Route The Remote Network Is 172.16.1.0, With A Mask Of 255.255.255.0, The Next Hop Is 172.16.2.1, At A Cost Of 5 Hops
VERIFYING STATIC ROUTE CONFIGURATION
After Static Routes Are Configured It Is Important To Verify That They Are Present In The Routing Table And That Routing Is Working As Expected.
The Command:
Router#Show Running-Config
Is Used To View The Active Configuration In RAM To Verify That The Static Route Was Entered Correctly. The Show Ip Route Command Is Used To Make Sure That The Static Route Is Present In The Routing Table.
USE THE FOLLOWING STEPS TO VERIFY STATIC ROUTE CONFIGURATION:
Router# Show Running-Config
The Command Show Running-Config
EXAMPLE: Remove All Currently Configured Static Routes On R3 Than Configure A Default Route On R3
R3#Show Run | Include Ip Route
Ip Route 10.63.10.0 255.255.255.0 10.63.23.1
Ip Route 10.63.20.0 255.255.255.0 10.63.23.1
R3#Configure Terminal
Enter Configuration Commands, One Per Line. End With CNTL/Z.
R3(Config)#No Ip Route 10.63.10.0 255.255.255.0 10.63.23.1
R3(Config)#No Ip Route 10.63.20.0 255.255.255.0 10.63.23.1
R3(Config)#Ip Route 0.0.0.0 0.0.0.0 10.63.23.1
R3(Config)#End
R3#
TROUBLESHOOTING STATIC ROUTE CONFIGURATION:
USE FROM PRIVILEGED EXEC MODE ON THE ROUTER, Ping To A Node On The Remote Network. The Ping Fails. Now Use The Traceroute Command From Your Router To The Address That Was Used In The Ping Statement. Note Where The Traceroute Fails.
The “Traceroute Indicates” That The ICMP Packet Was Returned From An Intermediate Router But Not From Our Destination. This Implies That The Trouble Exists Between The Intermediate Router And The Destination.
TROUBLESHOOTING STATIC ROUTES COMMAND:
USEFUL CONTROL COMMANDS:
Clear Ip Route *
Clear Ip Route [Network] [Mask]
Clear Arp
NOTE:
Router#Show IP Protocols Summary
Index Process Name
0 Connected
1 Static
2 Ospf 45
3 Rip
Router#
MANAGING IP ROUTING INFORMATION
Problems Do Arise, And When They Do, It Is Best To Start Slowly By Verifying That What You Believe To Be Happening Is In Fact Happening. The
USEFUL DISPLAY COMMANDS:
Show Ip Route
Show Ip Route Connected
Show Ip Route [Address/Hostname]
Show Arp
Show Ip Protocol
Show Ip Masks
Show Ip Masks [Network Address]
Traceroute
DEFAULT ROUTE:
A Default Route (Also Known As The Gateway Of Last Resort) Is A Special Type Of Static Route. Where A Static Route Specifies A Path A Router Should Use To Reach A Specific Destination, A Default Route Specifies A Path The Router Should Use If It Doesn’t Know How To Reach The Destination.
Default Route Is The Network Route Used By A Router When There Is No Other Known Route Exists For A Given IP Datagram's Destination Address. All The IP Datagrams With Unknown Destination Address Are Sent To The Default Route.
To Route Traffic To A Non-Connected Host Or Network, You Must Define A Static Route To The Host Or Network Or, At A Minimum, A Default Route For Any Networks To Which The ASA Is Not Directly Connected.
For Example, When There Is A Router Between A Network And The ASA.
Without A Static Or Default Route Defined, Traffic To Non-Connected Hosts Or Networks Generates The Following Error Message:
%ASA-6-110001: No Route To Dest_Address From Source_Address
DEFAULT ROUTES ARE Used To Route Packets With Destinations That Do Not Match Any Of The Other Routes In The Routing Table. Routers Are Typically Configured With A Default Route For Internet-Bound Traffic, Since It Is Often Impractical And Unnecessary To Maintain Routes To All Networks In The Internet.
Default Route A Route That Is Used When No Other Routes For The Destination Are Found In The Routing Table.
For Example, If A Router Or End System Cannot Find A Network Route Or Host Route For The Destination, The Default Route Is Used. Rather Than Being Configured With Routes For All The Network IDs In The Internet Work, The Default Route Is Used To Simplify The Configuration Of End Systems Or Routers.
CONFIGURING STATIC DEFAULT ROUTE:
There Is A Special Kind Of Static Route Called A Default Route. Sometimes A Default Route Is Called A “Zero / Zero” Route. This Is Because The Network And Subnet You Are Specifying, As The Destination For The Traffic It Would Match, Are All Zeros. A Default Route Says “For Any Traffic That Does Not Match A Specific Route In The Routing Table, Send That Traffic To This Destination”. In Other Words, A Default Route Is A “Catch-All”.
A Default Route Is Actually A Special Static Route That Uses This Format:
THERE ARE TWO WAYS TO CREATE A DEFAULT ROUTE: The First Is To Use The Same Command That You Used For A Static Route But Use The 0.0.0.0 Network As Your Destination With A Subnet Mask Of 0.0.0.0
FOR EXAMPLE:To Establish A Default Route To Send Traffic Out Serial 0/0 Destined For Any Network Not Learned Through Dynamic Or Static Means, Type The Following:
THE SYNTAX FOR THE GLOBAL CONFIGURATION COMMAND USED TO ENTER A STATIC ROUTE IS:
Ip Route {Destination Prefix} {Destination Prefix Mask} {Interface Or Forwarding Router’s Ip Address}
Ip Route 0.0.0.0 0.0.0.0 [Next-Hop-Address | Outgoing Interface]
IP Route 0.0.0.0 0.0.0.0 Serial 0/0
The 0.0.0.0 Mask, When Logically Anded To The Destination IP Address Of The Packet To Be Routed, Will Always Yield The Network 0.0.0.0. If The Packet Does Not Match A More Specific Route In The Routing Table, It Will Be Routed To The 0.0.0.0 Network.
If You Chose To Specify The Next-Hop Ip Address Of The Router, You Could Type The Following Instead (Assuming A Next-Hop Address).
R3(Config)#Ip Route 0.0.0.0 0.0.0.0 10.63.23.1
R3(Config)#End
R3#
USE THE FOLLOWING STEPS TO CONFIGURE DEFAULT ROUTES:
STEP 1: Enter Global Configuration Mode.
STEP 2: Type The Ip Route Command With 0.0.0.0 For The Prefix And 0.0.0.0 For The Mask. The Address Option For The Default Route Can Be Either The Local Router Interface That Connects To The Outside Networks Or The Ip Address Of The Next-Hop Router.
STEP 3: Exit Global Configuration Mode.
STEP 4: Use The Copy Running-Config Startup-Config Command To Save The Active Configuration To Nvram.
To Add A Default Route Using A Gateway Ip Address (Called As Gateway Of Last Resort) As A Next Hop Router.
CiscoRouter(Config)# IP Route 0.0.0.0 0.0.0.0 10.10.10.10
If You Want To Use A Local Exit Interface.
Ciscorouter(Config)# IP Route 0.0.0.0 0.0.0.0 Serial0/0/1
EXAMPLE – 3: FOR STATIC ROUTE AND DEFAULT ROUTES:
We're Going To Use The Ip Route Command To Create Static Routes. The Values That Follow The IP Route Command Can Be Tricky At First. The Destination Network, A Subnet Mask, And One Of The Following will follow the IP Route Command:
THAT'S A VERY IMPORTANT DETAIL TO NOTE: So I'll Mention It Again. If You Decide To Configure A Static Route On A Cisco Router Using An IP Address, It Has To Be The IP Address Of The Downstream Router. If You Want To Specify An Interface, It Has To Be The Local Router's Interface.
EXAMPLE:
Router1(Config)#IP Route 172.10.1.0 255.255.255.0 200.1.1.2 (Next-Hop IP Address)
OR
Router1(Config)#IP Route 172.10.1.0 255.255.255.0 Serial0 ( Local Exit Interface)
You Can Also Write A Static Route That Matches Only One Destination. This Is A Host Route, And Has 255.255.255.255 For A Mask. If The Above Static Routes Should Only Be Used To Send Packets To 172.10.1.1 The Following Commands Would Do The Job.
Router1(Config)#IP Route 172.10.1.1 255.255.255.255 200.1.1.2 (Next-Hop IP Address)
OR
Router1(Config)#IP Route 172.10.1.1 255.255.255.255 Serial0 ( Local Exit Interface)
FINALLY: A Default Static Route Serves As A Gateway Of Last Resort. If There Are No Matches For A Destination In The Routing Table, The Default Route Will Be Used. Default Routes Use All Zeroes For Both The Destination And Mask, And Again A Next-Hop Ip Address Or Local Exit Interface Can Be Used.
Router1(Config)#IP Route 0.0.0.0 0.0.0.0 200.1.1.2 (Next-Hop IP Address)
OR
Router1(Config)#IP Route 0.0.0.0 0.0.0.0 Serial0 ( Local Exit Interface)
VERIFYING YOUR CONFIGURATION
To Verify That You Have Properly Configured Static Routing, Enter The Show Ip Route Command And Look For Static Routes Signified By The “S.” You Should See Verification Output Similar To The Following Example.
Router1# Show IP Route
“Show Ip Route”Is The First Command To Use To Check For Network Convergence. As You Examine The Routing Table, It Is Important To Look For The Routes That You Expect To Be In The Routing Table As Well As For Those That Should Not Be In The Routing Table.
GNS3 TOPOLOGY - IPV4 - LAB CONFIGURATION FOR STATIC ROUTE & STATIC DEFAULT ROUTE:
The General Format Of A Static Route Command On A Cisco Router Is:
Router(Config)# IP Route [Destination Network] [Mask] [Gateway Address]
LAB SETUP (GNS3 – IPV4):
In This Lab, You Will Configure Static Routes Between All Three Routers. This Will Allow Your Routers To Route Packets So That All Routers And All Hosts Will Be Able To Reach (Ping) Each Other. Once Your Configuration Is Complete, You Will Use Basic Techniques To Test Your Network’s connectivity.
Type no and press enter to avoid startup configuration Now you are in user exec mode.
Continue with configuration dialog? [yes/no]: no
Press RETURN to get started!
Router>
Configuration Serial Interface DCE (cable)
Use the Router(config-if)#clock rate 64000 command on the DCE end of the serial link to achieve this.
Set The Clock Rate For A Router With A DCE Cable To 64K Router12520(Config-If)Clock Rate 64000
The Following Example Shows How To Configure Serial Interface 0 With A Clock Rate That Is Rounded To The Nearest Value That Is Supported By The Hardware.
Router12520(Config-If)# Clock Rate 64000
NOTE: Test And Troubleshoot As Necessary. Use The Context Sensitive Help, Previous Labs, Your Books And /Or Handouts And If Your Still Having Problems Ask Your Partner Or Ask The Instructor For Assistance.
STEP 1: CONFIGURING STATIC ROUTES.
NOTE: On Each Router Configure A Separate And Specific Static Route For Each Network Or Subnet. You Do Not Need To Configure Static Routes For The Router’s Directly Connected Network (S) Because Like A Host, By Configuring The IP Address And Subnet Mask On An Interface Tells The Router That It Belongs To That Network/Subnet.
ROUTER1:
Router1(Config)# Ip Route 172.16.3.0 255.255.255.0 172.16.2.1
Router1(Config)# Ip Route 192.168.2.0 255.255.255.0 192.168.1.1
ROUTER2:
Router2(Config)# Ip Route 172.16.1.0 255.255.255.0 172.16.2.2
Router2(Config)# Ip Route 192.168.1.0 255.255.255.0 172.16.2.2
Router2(Config)# Ip Route 192.168.2.0 255.255.255.0 172.16.2.2
Router3:
Router3(Config)# Ip Route 172.16.1.0 255.255.255.0 192.168.1.2
Router3(Config)# Ip Route 172.16.2.0 255.255.255.0 192.168.1.2
Router3(Config)# Ip Route 172.16.3.0 255.255.255.0 192.168.1.2
VERIFY AND VALIDATE: OUTPUTS ON ROUTER1, ROUTER2 & ROUTER3:
ON ROUTER2:
Router2#Show Ip Route
(Output Omitted)
Gateway Of Last Resort Is Not Set
172.16.0.0/24 Is Subnetted, 3 Subnets
S 172.16.1.0 [1/0] Via 172.16.2.2
C 172.16.2.0 Is Directly Connected, Serial0
C 172.16.3.0 Is Directly Connected, Ethernet0
S 192.168.1.0/24 [1/0] Via 172.16.2.2
S 192.168.2.0/24 [1/0] Via 172.16.2.2
ROUTER1:
Router1#Show Ip Route
(Output Omitted)
Gateway Of Last Resort Is Not Set
172.16.0.0/24 Is Subnetted, 3 Subnets
C 172.16.1.0 Is Directly Connected, Ethernet0
C 172.16.2.0 Is Directly Connected, Serial0
S 172.16.3.0 [1/0] Via 172.16.2.1
C 192.168.1.0/24 Is Directly Connected, Serial1
S 192.168.2.0/24 [1/0] Via 192.168.1.1
ROUTER3:
Router3#Show Ip Route
(Output Omitted)
Gateway Of Last Resort Is Not Set
172.16.0.0/24 Is Subnetted, 3 Subnets
S 172.16.1.0 [1/0] Via 192.168.1.2
S 172.16.2.0 [1/0] Via 192.168.1.2
S 172.16.3.0 [1/0] Via 192.168.1.2
C 192.168.1.0/24 Is Directly Connected, Serial0
C 192.168.2.0/24 Is Directly Connected, Ethernet0
STEP 2:CONFIGURING SUMMARY STATIC ROUTES:
NOTE:The Configuration Of The Routers In Step 1 Works Just Great And Is A Valid Way To Configure Routing On These Networks. Earlier, We Noticed That The Network 172.16.0.0 Is Divided Into Several Subnets.
The Router3 Router Does Not Really Need Separate Static Routes For Each Subnet, Since All Of The 172.16.0.0 Subnets Can Be Reached Via The Same Next-Hop IP Address.
Router1. Let’s Reconfigure The Static Routes On Router3 So That It Only Uses A Single Static Route To Reach All Of The 172.16.0.0 Subnets.
ON ROUTER1
ON ROUTER2
ON ROUTER3
Router3(Config)# No Ip Route 172.16.1.0 255.255.255.0 192.168.1.2
Router3(Config)# No Ip Route 172.16.2.0 255.255.255.0 192.168.1.2
Router3(Config)# No Ip Route 172.16.3.0 255.255.255.0 192.168.1.2
Router3(Config)# Ip Route 172.16.0.0 255.255.0.0 192.168.1.2
VERIFY AND VALIDATE:
All Hosts And All Routers Should Be Able To Ping Every Interface In The Network. Do A “Show Running-Config” And Notice The Static Routes That You Entered.
Router3# Show Ip Route
OUTPUTS
Router3#Show Ip Route
(Output Omitted)
Gateway Of Last Resort Is Not Set
S 172.16.0.0/16 [1/0] Via 192.168.1.2
C 192.168.1.0/24 Is Directly Connected, Serial0
C 192.168.2.0/24 Is Directly Connected, Ethernet0
STEP 3:CONFIGURING DEFAULT STATIC ROUTES
NOTE:Both Step 1 And Step 2 Are Acceptable Ways To Configure Routing For These Networks.
We Notice That The 172.16.3.0/24 And The 192.168.2.0/24 Networks Are “Stub Networks,” Meaning That There Is Only One Way Out (Both Via Router1).
ROUTER1:
No Changes
ROUTER2:
First, Remove The Current Static Routes:
Router2(Config)# No Ip Route 172.16.1.0 255.255.255.0 172.16.2.2
Router2(Config)# No Ip Route 192.168.1.0 255.255.255.0 172.16.2.2
Router2(Config)# No Ip Route 192.168.2.0 255.255.255.0 172.16.2.2
Now, Add The New Default Static Route:
Router2(Config)# Ip Route 0.0.0.0 0.0.0.0 172.16.2.2
ROUTER3:
First, Remove The Current Static Routes:
Router3(Config)# No Ip Route 172.16.0.0 255.255.0.0 192.168.1.2
Now, Add The New Default Static Route:
Router3(Config)# IP Route 0.0.0.0 0.0.0.0 192.168.1.2
VERIFY AND VALIDATE:
All Hosts And All Routers Should Be Able To Ping Every Interface In The Network. Do A “Show Running-Config” And Notice The Static Routes That You Entered.
Router2# Show IP Route
OUTPUTS
Router3#Show IP Route
(Output Omitted)
Gateway Of Last Resort Is 192.168.1.2 To Network 0.0.0.0
C 192.168.1.0/24 Is Directly Connected, Serial0
C 192.168.2.0/24 Is Directly Connected, Ethernet0
S* 0.0.0.0/0 [1/0] Via 192.168.1.2
Save Your Current Configuration To NVRAM.
END OF LAB (IPV4 - STATIC ROUTE & STATIC DEFAULT ROUTE).
IPV6 - STATIC AND DEFAULT ROUTES:
INTRODUCTION:
Static Routes Are Manually Configured. They Work Well In Simple Networks. Configuring And Using Them Properly Can Improve Network Performance And Ensure Enough Bandwidth For Important Applications.
FEATURES OF IPV6 STATIC ROUTES:
Similar To IPv4 Static Routes, Ipv6 Static Routes Work Well In Simple IPv6 Network Environments.
Their Major Difference Lies In The Destination And Next Hop Addresses. IPv6 Static Routes Use IPv6 Addresses, Whereas Ipv4 Static Routes Use IPv4 Addresses. IPv6 Static Routes Do Not Support VPN Instance.
DEFAULT IPV6 ROUTE:
An Ipv6 Static Route With A Destination Prefix Of: :/0 Is A Default Ipv6 Route.
CONFIGURING AN IPV6 STATIC ROUTE:
In Small IPv6 Networks, IPv6 Static Routes Can Be Used To Forward Packets. In Comparison To Dynamic Routes, It Helps To Save Network Bandwidth.
CONFIGURATION PREREQUISITES:
CONFIGURE AN IPv6 STATIC ROUTE:
IPv6 Route-Static IPv6-Address Prefix-Length { Interface-Type Interface-Number [ Next-Hop-Address ] | Next-Hop-Address | Vpn-Instance D-Vpn-Instance-Name Nexthop-Address } [ Preference Preference-Value ]
IPv6 Route-Static Vpn-Instance S-Vpn-Instance-Name IPv6-Address Prefix-Length { Interface-Type Interface-Number [ Next-Hop-Address ] | Nexthop-Address [ Public ] | Vpn-Instance D-Vpn-Instance-Name Nexthop-Address } [ Preference Preference-Value ]
Remarks: Use Either Approach. The Default Preference Of Ipv6 Static Routes Is 60.
DISPLAYING AND MAINTAINING IPv6 STATIC ROUTES: Display IPv6 Static Route Information:
Display Ipv6 Routing-Table Protocol Static [ Inactive | Verbose ] [ | { Begin | Exclude | Include } Regular-Expression ]
Remove All Ipv6 Static Routes:
Delete Ipv6 [ Vpn-Instance Vpn-Instance-Name ] Static-Routes All
STATIC ROUTES IN IPV6:
Use The IPv6 Route Command To Configure IPv6 Static Routes.
SUMMARY STEPS:
1. Enable
2. Configure Terminal
3. IPv6 Route IPv6-Prefix/Prefix-Length {Ipv6-Address | Interface-Type Interface-Number [Ipv6-Address]}
EXAMPLECONFIGURING IPV6 DEFAULT AND STATIC ROUTES:
You Can Add A Default Route And Static Routes Using The Ipv6 Route Command. To Configure An Ipv6 Default Route And Static Routes, Perform The Following Steps:
STEP 1: To Add The Default Route, Use The Following Command:
Hostname(Config)# Ipv6 Route If_Name ::/0 Next_Hop_Ipv6_Addr
The Address ::/0 Is The Ipv6 Equivalent Of "Any."
STEP 2: (Optional) Define Ipv6 Static Routes. Use The Following Command To Add An Ipv6 Static Route To The Ipv6 Routing Table:
Hostname(config)# ipv6 route if_name destination next_hop_ipv6_addr [admin_distance]
Router(Config)# Ipv6 Route 2001:0db8::/32 Serial 0
IPV6 STATIC ROUTING CONFIGURATION EXAMPLE:
1. Enable Ipv6 Routing And Cisco Express Forwarding (Cef) On Each Router. 2811a#Config T
2811a(Config)#Ipv6 Unicast-Routing
2811a(Config)#Ipv6 Cef
2811b#Config T
2811b(Config)#Ipv6 Unicast-Routing
2811b(Config)#Ipv6 Cef
2811c#Config T
2811c(Config)#Ipv6 Unicast-Routing
2811c(Config)#Ipv6 Cef
2. Configure Ipv6 Addresses On Router 2811 A.
2811a(Config)#Interface Fastethernet 0/0
2811a(Config-If)#Ipv6 Address 2001::10:1/112
2811a(Config-If)#Interface Serial 0/0/0
2811a(Config-If )Ipv6 Address 2001::20:1/112
2811a(Config-If)#Interface Serial 0/1/0
2811a(Config-If)#Ipv6 Address 2001::30:1/112
2811a(Config-If)#Exit
3. Configure Ipv6 Addresses On Router 2811 B.
2811b(Config)#Interface Fastethernet 0/0
2811b(Config-If)# Ipv6 Address 2001::40:1/112
2811b(Config-If)#Interface Serial 0/1/0
2811b(Config-If)#Ipv6 Address 2001::30:2/112
2811b(Config-If)#Exit
4. Configure Ipv6 Addresses On Router 2811 C.
2811c(Config)#Interface Fastethernet 0/0
2811c(Config-If)# Ipv6 Address 2001::50:1/112
2811c(Config-If)#Interface Serial 0/0/0
2811c(Config-If)#Ipv6 Address 2001::20:2/112
2811c(Config-If)#Exit
5. Configure Two Ipv6 Static Routes On Router 2811 A.
2811a(Config)#Ipv6 Route 2001::40:0/112 2001::30:2
2811a(Config)#Ipv6 Route 2001::50:0/112 2001::20:2
2811a(Config)#Exit
2811a#Copy Run Start
The Static Routes Will Allow Router 2811 A To Communicate With The Rest Of The Network.
6. Configure A Ipv6 Default Route On Router 2811 B. 2811b(Config)#Ipv6 Route ::/0 2001::30:1
2811b(Config)#Exit
2811b#Copy Run Start
This Default Route Will Allow Router 2811 B To Communicate With The Rest Of The Network. Router 2811 B Will Use Router 2811 A As A Gateway Of Last Resort.
7. Configure A Ipv6 Default Route On Router 2811 C.
2811c(Config)#Ipv6 Route ::/0 2001::20:1
2811c(Config)#Exit
2811c#Copy Run Start
This Default Route Will Allow Router 2811 C To Communicate With The Rest Of The Network. Router 2811 C Will Use Router 2811 A As A Gateway Of Last Resort.
IPV6 - LAB CONFIGURING IPV6 DEFAULT AND STATIC ROUTES:
You Will Learn Two Types Of Ipv6 Static Routes In This Lab Which Are The Standard Administrative Static Routes Where You Have The Ability To Set The Administrative Distance Following The Route Statement As Well As Default Static Routes Used As A Last Resort Route If No Particular Route Exist For A Destination Of Incoming Traffic.
Before You Can Configure Ipv6 Routing On A Cisco Router You Must First Enable The Cisco Router To Route IPv6 By Executing The Command IPv6 Unicast-Routing In Global Configuration Mode.
When Configuring An Ipv6 Static Route You’ll Use The Ipv6 Route X:X:X:X::/X X:X:X:X::X Whereas The First Ipv6 Address In The Static Route Statement Is The Network And The 2nd Ipv6 Address Is The Next Hop In The Transit Path To Reach That Network.
Keep In Mind The Administrative Distance Of 255 Is Considered “Unreachable”. An Example Of An Ipv6 Static Route Using An Administrative Distance Of 224 Is; IPv6 Route 2001:ABC:123:FADE::0/64 2001:ABAD:BEEF:1234::1 224. Keep In Mind When Using An IPv6 Link-Local Address As The Next Hop You Must Specify The Egress (Exiting) Interface.
Ipv6 Route 2001:ABC:123:FADE::0/64 Serial1/1 FE80::C800:10FF:FE1C:8 224.
You Can Configure An Ipv6 Static Default Route By Using ::/128 As The Destination Network Followed By The Next-Hop. I.E; Ipv6 Route ::/128 2001:ABAD:BEEF:1234::1 200
LAB INSTRUCTION:
In This Lab You Will Configure A Static Route On Router A To Reach Router B′S Loopback0 Network Using Router B′S Serial1/1 Ipv6 Link-Local Address As The Next-Hop Then Configure A Default Ipv6 Route On Router B Using Router A′S Serial1/1 Ipv6 Link-Local Address As The Next-Hop.
LAB SETUP (GNS3 – IPV6):
STEP 1:
To Configure This Static Route Statement You Must First Obtain The Ipv6 Link-Local Address Of Router B′S Serial1/1 Interface As Shown Below:
Router B>Enable
Router B#Show Ipv6 Interface Serial1/1
Serial1/1 Is Up, Line Protocol Is Up
Ipv6 Is Enabled, Link-Local Address Is Fe80::C800:10ff:Fe1c:8
No Virtual Link-Local Address(Es):
Description: ### Link To Frame Relay Switch ###
Global Unicast Address(Es):
2001:Abad:Beef:1221::2, Subnet Is 2001:Abad:Beef:1221::/64
Joined Group Address(Es):
Ff02::1
Ff02::1:Ff00:2
Ff02::1:Ff1c:8
Mtu Is 1500 Bytes
Icmp Error Messages Limited To One Every 100 Milliseconds
Icmp Redirects Are Enabled
Icmp Unreachables Are Sent
Nd Dad Is Enabled, Number Of Dad Attempts: 1
Nd Reachable Time Is 30000 Milliseconds (Using 17988)
Router B#
Once You’ve Obtained Router B′S Ipv6 Link-Local Address You Can Now Configure The Static Route Statement On Router A As Shown Below:
Router A>Enable
Router A#Configure Terminal
Enter Configuration Commands, One Per Line. End With Cntl/Z.
Router A(Config)#Ipv6 Unicast-Routing
Router A(Config)#$2001:Abad:Beef:2002::0/64 Serial1/1
Fe80::C800:10ff:Fe1c:8
Router A(Config)#End
Router A#
STEP 2:
Configure A Default Static Route On Router B Pointing Towards Router A′S Serial1/1 Globally Unique Ipv6 Unicast Address To Reach All Unknown Networks Including The Network Assigned To Router A′S Loopback0 Interface.
Router B#Configure Terminal
Enter Configuration Commands, One Per Line. End With Cntl/Z.
Router B(Config)#Ipv6 Route Unicast-Routing
Router B(Config)#Ipv6 Route ::/0 2001:Abad:Beef:1221::1
Router B(Config)#End
Router B#
STEP 3:
Verify That Router B′S Loopback0 Has IPv6 Communication To Router A′S Loopback0 Network Using Ping.
Router B#Ping 2001:ABAD:BEEF:1001::1 Source Loopback0
Type Escape Sequence To Abort. Sending 5, 100-Byte ICMP Echos To 2001:ABAD:BEEF:1001::1, Timeout
Is 2 Seconds: Packet Sent With A Source Address Of 2001:ABAD:BEEF:2002::1 !!!!! Success Rate Is 100 Percent (5/5), Round-Trip Min/Avg/Max = 8/37/68 Ms
Router B#
END OF LAB (IPV6 - STATIC ROUTE & STATIC DEFAULT ROUTE).
DYNAMIC ROUTES:
NOTE: Dynamic Routing Lab We’ll be See Later On this site (By Each Dynamic Routing Protocol Separately).
The Opposite Of Static Route Is A Dynamic Route. A Dynamic Routing Table Is Created, Maintained, And Updated By A Routing Protocol Running On The Router. (Examples Of Routing Protocols Are As Follows: Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Enhanced Interior Gateway Routing Protocol (EIGRP), Open Shortest Path First (OSPF))
A Router With Dynamically Configured Routing Tables Is Known As A Dynamic Router. Dynamic Routes Are Routes That A Router Learns By Using A Routing Protocol. Routing Protocols Will Learn About Routes From Other Neighbouring Routers Running The Same Routing Protocol. Dynamic Routing Protocols Share Network Numbers A Router Knows About And How To Reach These Networks. Through This Sharing Process, A Router Can Learn About All Of The Reachable Network Numbers In The Network. Using A Routing Protocol To Determine The Best Path.
If One Route Becomes Less Preferred, The Route Being Used May Change. With Dynamic Routes, Routes Communicate With Each Other And Exchange Routing Information That Are Called Dynamic Routing.
Dynamic Routing Uses A Dynamic Routing Protocol To Automatically Select The Best Route To Put Into The Routing Table. So Instead Of Manually Entering Static Routes In The Routing Table, Dynamic Routing Automatically Receives Routing Updates, And Dynamically Decides Which Routes Are Best To Go Into The Routing Table. Its This Intelligent And Hands-Off Approach That Makes Dynamic Routing So Useful. This Communication Is Facilitated By A Routing Protocol, A Series Of Periodic Or On-Demand Messages Containing Routing Information That Is Exchanged Between Routers.
The Network Protocol (Dynamic Routing Protocols) Adjusts The Best Path Automatically, Based On Network Traffic Or Topology. Changes In Dynamic Routes Are Shared With Other Routers In The Network. The Cisco Routers Can Use IP Routing Protocols, A Routing Protocol Is The Language A Router Speaks With Other Routers In Order To Share Information About The Reachability And Status Of Networks.
Dynamic Routing Protocols Not Only Perform These Path Determination And Route Table Update Functions But Also Determine The Next-Best Path If The Best Path To A Destination Becomes Unusable. The Capability To Compensate For Topology Changes Is The Most Important Advantage Dynamic Routing Offers Over Static Routing.
Obviously, For Communications To Occur The Communicators Must Speak The Same Language. There Are Eight Major IP Routing Protocols From Which To Choose; If One Router Speaks RIP And Another Speaks OSPF, They Cannot Share Routing Information Because They Are Not Speaking The Same Language. (We Have To Redistribute With Each Others Different Protocal) Subsequent Chapters Examine All The IP Routing Protocols In Current Use, And Even Consider How To Make A Router "Bilingual," But First It Is Necessary To Explore Some Characteristics And Issues Common To All Routing Protocols—IP Or Otherwise.
NOTE: Routers Do Share Dynamic Routing Information With Each Other, Which Increases CPU, RAM, And Bandwidth Usage. However, Routing Protocols Are Capable Of Dynamically Choosing A Different (Or Better) Path When There Is A Change To The Routing Infrastructure.
DYNAMIC ROUTING PROTOCOL BASICS:
All Dynamic Routing Protocols Are Built Around An Algorithm. Generally, An Algorithm Is A Step-By-Step Procedure For Solving A Problem.
A ROUTING ALGORITHM MUST, AT A MINIMUM, SPECIFY THE FOLLOWING:
A FEW ISSUES: Common To Any Routing Protocol Are Path Determination, Metrics, Convergence, And Load Balancing.
Classifying DYNAMIC ROUTING PROTOCOLS Is Based On Where They Are Used. This Criterion Allows Us To Distinguish Between Two Major Solutions:
1. Interior Gateway Protocols (IGP)
2. Exterior Gateway Protocols (EGP)
COMMON INTERIOR GATEWAY PROTOCOLS ARE:
Exterior Gateway Protocols (currently there is only one in use)
IGPS Are Designed To Work In Private Networks. EGPS Are Used To Provide Paths In The Public Network (Internet).
We Can Also Classify Routing Protocols Based On The Algorithm They Use To Distribute And Maintain Information (Routing Table).
DYNAMIC ROUTING ALGORITHM:
Dynamic Routing Algorithms Can Be Supplemented With Static Routes Where Appropriate. A Router Of Last Resort (A Router To Which All Unroutable Packets Are Sent), For Example, Can Be Designated To Act As A Repository For All Unroutable Packets, Ensuring That All Messages Are At Least Handled In Some Way.
Each Protocol Uses A Slightly Different Algorithm For Choosing The Best Route Between Two Addresses On The Network. The Algorithm Is The “Intelligent” Part Of A Dynamic Protocol Because The Algorithm Is Responsible For Deciding Which Route Is Best And Should Be Added To The Local Routing Table.
RIP And BGP Use Distance Vector Algorithms, Where OSPF Uses Link-State Or A Shortest Path First Algorithm.
VECTOR ALGORITHMS: Are Essentially Based On The Number Of Hops Between The Originator And The Destination In A Route, Possibly Weighting Hops Based On How Reliable, Fast, And Errorfree They Are.
THE LINK-STATE ALGORITHM: Used By OSPF Is Called The Dijkstra Algorithm. Link-State Treats Each Interface As A Link, And Records Information About The State Of The Interface. The Dijkstra Algorithm Creates Trees To Find The Shortest Paths To The Routes It Needs Based On The Total Cost Of The Parts Of The Routes In The Tree.
DYNAMIC ROUTING CATEGORIESThere Are Two Distinct Categories Of Dynamic Routing Protocols:
The Distance Vector Routing Approach Determines The Direction, Or Vector, And Distance To Any Link In An Internetwork. The Link-State Approach Recreates The Exact Topology Of An Entire Internetwork.
Examples: Of Distance -Vector Protocols Include RIP And IGRP.
Examples: Of Link-State Protocols Include OSPF And IS-IS.
NOTE: EIGRP Exhibits Both Distance-Vector And Link-State Characteristics, And Is Considered A Hybrid Protocol.
DISTANCE VECTOR ROUTING PROTOCOL FEATURES:
The Distance Vector Routing Algorithm Passes Periodic Copies Of A Routing Table From Router To Router. These Regular Updates Between Routers Communicate Topology Changes. The Distance Vector Routing Algorithm Is Also Known As The Bellman-Ford Algorithm.
Each Router Receives A Routing Table From Its Directly Connected Neighbour Routers. Router B Receives Information From Router A. Router B Adds A Distance Vector Number, Such As A Number Of Hops. This Number Increases The Distance Vector. Then Router B Passes This New Routing Table To Its Other Neighbour, Router C. This Same Step-By-Step Process Occurs In All Directions Between Neighbour Routers.
The Algorithm Eventually Accumulates Network Distances So That It Can Maintain A Database Of Network Topology Information. However, The Distance Vector Algorithm Does Not Allow A Router To Know The Exact Topology Of An Internetwork Since Each Router Only Sees Its Neighbour Routers.
Each Router That Uses Distance Vector Routing First Identifies Its Neighbours. The Interface That Leads To Each Directly Connected Network Has A Distance Of 0. As The Distance Vector Discovery Process Proceeds, Routers Discover The Best Path To Destination Networks Based On The Information They Receive From Each Neighbour. Router A Learns About Other Networks Based On The Information That It Receives From Router B. Each Of The Other Network Entries In The Routing Table Has An Accumulated Distance Vector To Show How Far Away That Network Is In A Given Direction.
Routing Table Updates Occur When The Topology Changes. As With The Network Discovery Process, Topology Change Updates Proceed Step-By-Step From Router To Router. Distance Vector Algorithms Call For Each Router To Send Its Entire Routing Table To Each Of Its Adjacent Neighbours. The Routing Tables Include Information About The Total Path Cost As Defined By Its Metric And The Logical Address Of The First Router On The Path To Each Network Contained In The Table.
An Analogy Of Distance Vector Could Be The Signs Found At A Highway Intersection. A Sign Points Toward A Destination And Indicates The Distance To The Destination. Further Down The Highway, Another Sign Points Toward The Destination, But Now The Distance Is Shorter. As Long As The Distance Is Shorter, The Traffic Is On The Best Path.
ALL DISTANCE PRO -VECTOR ROUTING TOCOLS SHARE SEVERAL KEY CHARACTERISTICS:
A Distance - Vector Routing Protocol Begins By Advertising Directly-Connected Networks To Its Neighbors. These Updates Are Sent Regularly (RIP – Every 30 Seconds; IGRP – Every 90 Seconds).
Neighbors Will Add The Routes From These Updates To Their Own Routing Tables. Each Neighbor Trusts This Information Completely, And Will Forward Their Full Routing Table (Connected And Learned Routes) To Every Other Neighbor. Thus, Routers Fully (And Blindly) Rely On Neighbors For Route Information, A Concept Known As Routing By Rumor.
There Are Several Disadvantages To This Behavior. Because Routing Information Is Propagated From Neighbor To Neighbor Via Periodic Updates, Distance-Vector Protocols Suffer From Slow Convergence.This, In Addition To Blind Faith Of Neighbor Updates, Results In Distance-Vector Protocols Being Highly Susceptible To Routing Loops.
Distance-Vector Protocols Utilize Some Form Of Distance To Calculate A Route’s Metric, RIP Uses HopCount As Its Distance Metric, And IGRP Uses A Composite Of Bandwidth And Delay.
LINK-STATE ROUTING PROTOCOL FEATURES:
The Other Basic Algorithm That Is Used For Routing Is The Link-State Algorithm. The Link-State Algorithm Is Also Known As Dijkstra's Algorithm Or As The Shortest Path First (SPF) Algorithm.
LINK-STATE ROUTING USES THE FOLLOWING FEATURES:
NETWORK DISCOVERY PROCESSES FOR LINK STATE ROUTING
When Routers Exchange LSAS, They Begin With Directly Connected Networks For Which They Have Information. Each Router Constructs A Topological Database That Consists Of All The Exchanged LSAS.
The SPF Algorithm Computes Network Reachability. The Router Constructs This Logical Topology As A Tree, With Itself As The Root. This Topology Consists Of All Possible Paths To Each Network In The Link-State Protocol Internetwork. The Router Then Uses SPF To Sort These Paths. The Router Lists The Best Paths And The Interfaces To These Destination Networks In The Routing Table. It Also Maintains Other Databases Of Topology Elements And Status Details.
The First Router That Learns Of A Link-State Topology Change Forwards The Information So That All Other Routers Can Use It For Updates. Common Routing Information Is Sent To All Routers In The Internetwork. To Achieve Convergence, Each Router Learns About Its Neighbour Routers. This Includes The Name Of Each Neighbour Router, The Interface Status, And The Cost Of The Link To The Neighbour. The Router Constructs An LSA Packet That Lists This Information Along With New Neighbours, Changes In Link Costs, And Links That Are No Longer Valid. The LSA Packet Is Then Sent Out So That All Other Routers Receive It.
When A Router Receives An LSA, It Updates The Routing Table With The Most Recent Information. The Accumulated Data Is Used To Create A Map Of The Internetwork And The SPF Algorithm Is Used To Calculate The Shortest Path To Other Networks. Each Time An LSA Packet Causes A Change To The Link-State Database, SPF Recalculates The Best Paths And Updates The Routing Table.
THERE ARE THREE MAIN CONCERNS RELATED TO LINK-STATE PROTOCOLS:
Routers That Use Link-State Protocols Require More Memory And Process More Data Than Routers That Use Distance Vector Routing Protocols. Link-State Routers Need Enough Memory To Hold All Of The Information From The Various Databases, The Topology Tree, And The Routing Table.
Initial Link-State Packet Flooding Consumes Bandwidth. In The Initial Discovery Process, All Routers That Use Link-State Routing Protocols Send LSA Packets To All Other Routers. This Action Floods The Internetwork And Temporarily Reduces The Bandwidth Available For Routed Traffic That Carries User Data. After This Initial Flooding, Link-State Routing Protocols Generally Require Minimal Bandwidth To Send Infrequent Or Event-Triggered LSA Packets That Reflect Topology Changes.
LINK-STATE ROUTING PROTOCOLS SHARE SEVERAL KEY CHARACTERISTICS:
Link-State Routing Protocols Were Developed To Alleviate The Convergence And Loop Issues Of Distance -Vector Protocols. Link-State Protocols Maintain Three Separate Tables:
Link-State Protocols Do Not “Route By Rumor.” Instead, Routers Send Updates Advertising The State Of Their Links (A Link Is A Directly-Connected Network). All Routers Know The State Of All Existing Links Within Their Area, And Store This Information In A Topology Table. All Routers Within An Area Have Identical Topology Tables.
The Best Route To Each Link (Network) Is Stored In The Routing (Or SHORTESTPATH) Table. If The State Of A Link Changes, Such As A Router Interface Failing, An Advertisement Containing Only This Link-State Change Will Be Sent To All Routers Within That Area. Each Router Will Adjust Its Topology Table Accordingly, And Will Calculate A New Best Route If Required.
By Maintaining A Consistent Topology Table Among All Routers Within An Area, Link-State Protocols Can Converge Very Quickly And Are Immune To Routing Loops.
Additionally, Because Updates Are Sent Only During A Link-State Change, And Contain Only The Change (And Not The Full Table), Link-State Protocols Are Less Bandwidth Intensive Than Distance-Vector Protocols. However, The Three Link-State Tables Utilize More RAM And CPU On The Router Itself.
Link-State Protocols Utilize Some Form Of Cost, Usually Based On Bandwidth, To Calculate A Route’s Metric. The Dijkstra Formula Is Used To Determine The Shortest Path.
ADVANTAGES OF DYNAMIC ROUTING
Dynamic Routing Over Static Routing Are Scalability And Adaptability. A Dynamically Routed Network Can Grow More Quickly And Larger, And Is Able To Adapt To Changes In The Network Topology Brought About By This Growth Or By The Failure Of One Or More Network Components.
With A Dynamic Routing Protocol, Routers Learn About The Network Topology By Communicating With Other Routers. Each Router Announces Its Presence, And The Routes It Has Available, To The Other Routers On The Network. Therefore, If You Add A New Router, Or Add An Additional Segment To An Existing Router, The Other Routers Will Hear About The Addition And Adjust Their Routing Tables Accordingly. You Don't Have To Reconfigure The Routers To Tell Them That The Network Has Changed. Similarly, If You Move A Network Segment, The Other Routers Will Hear About The Change. You Only Need To Change The Configuration Of The Router (Or Routers) That Connect The Segment That Moved. This Reduces The Chance That Errors Will Occur.
The Ability To Learn About Changes To The Network's Configuration Has Implications Beyond Adding New Segments Or Moving Old Ones. It Also Means That The Network Can Adjust To Failures. If A Network Has Redundant Paths, Then A Partial Network Failure Appears To The Routers As If Some Segments Got Moved (They Are Now Reached Via Alternate Paths), And Some Segments Have Been Removed From The Network (They Are Now Unreachable). In Short, There's No Real Difference Between A Network Failure And A Configuration Change. Dynamic Routing Allows The Network To Continue Functioning, Perhaps In A Degraded Fashion, When A Partial Failure Occurs.
THE DRAWBACKS OF DYNAMIC ROUTING:
I Would Be A Liar If I Told You That Dynamic Routing Has No Disadvantages. Chief Among The Disadvantages Is An Increase In Complexity. Communicating Information About Network Topology Is Not As Simple As Saying, "Hey, I Can Reach The Following Destinations..." Each Router Participating In The Dynamic Routing Protocol Must Decide Exactly What Information To Send To Other Routers; More Important, It Must Attempt To Select The Best Route For Reaching Other Destinations From The Candidates It Learns About From Other Routers. In Addition, If A Router Is Going To Adapt To Changes In The Network, It Must Be Prepared To Remove Old Or Unusable Information From Its Routing Table. How It Determines What Is Old Or Unusable Adds To The Complexity Of The Routing Protocol. Unfortunately, The Better A Protocol Handles The Various Different Situations In A Network, The More Complex It Is Likely To Be. This Complexity Tends To Lead To Errors In The Protocol's Implementation, Or Differences In How Vendors Interpret The Protocol.
In Order To Communicate Information About The Topology Of The Network, Routers Must Periodically Send Messages To Each Other Using A Dynamic Routing Protocol. These Messages Must Be Sent Across Network Segments Just Like Any Other Packets. But Unlike Other Packets In The Network, These Packets Do Not Contain Any Information To Or From A User. Instead, They Contain Information That Is Only Useful To The Routers. Thus, From The Users' Point Of View, These Packets Are Pure Overhead. On A Low-Speed Link, These Messages Can Consume Much Of The Available Bandwidth, Especially If The Network Is Large Or Unstable.
Finally, Some Or All Of The Machines In A Network May Be Unable To Speak Any Dynamic Routing Protocol, Or They May Not Speak A Common Protocol. If That Is The Case, Static Routing May Be Your Only Option.
With All The Disadvantages Listed Of Both Static And Dynamic Routing, You May Be Wondering What The Best Choice Is. Only You Can Say For Sure What Is Best For Your Network, But There Is A Reasonable Middle Ground That Limits The Complexity Of Dynamic Routing Without Sacrificing Its Scalability. This Middle Ground Is A Hybrid Scheme, In Which Part Of The Network Uses Static Routing And Part Uses Dynamic Routing.
SUMMARY:
There Are Two Types Of Routing That Can Be Configured On A Network Device- Static And Dynamic.
The Process That A Router Uses To Forward Packets Toward The Destination Network Is Called Routing. Decisions Are Based Upon The Destination IP Address Of Each Packet.
STATIC ROUTE OPERATIONS CAN BE DIVIDED INTO THESE THREE PARTS:
(1) First A Network Administrator Uses The Ip Route Command To Configure A Static Route.
(2) Then The Router Installs The Route In The Routing Table.
(3) Finally, The Route Is Used To Route Packets.
Static Routes Can Be Used For Backup Purposes. A Static Route Can Be Configured On A Router That Will Only Be Used When The Dynamically Learned Route Has Failed.
After Static Routes Are Configured, Verify They Are Present In The Routing Table And That Routing Works As Expected. Use The Command “Show Running-Config” To View The Active Configuration In RAM. The “Show Ip Route” Command Is Used To Make Sure That The Static Route Is Present In The Routing Table.
The Communication Used Between Routers Is Referred To As A Routing Protocol. The Goal Of A Routing Protocol Is To Build And Maintain The Routing Table.
A Routed Protocol Is Used To Direct User Traffic. A Routed Protocol Provides Enough Information In Its Network Layer Address To Allow A Packet To Be Forwarded From One Host To Another Based On The Addressing Scheme.
An AS Is A Collection Of Networks Under The Same Administration That Share A Common Routing Strategy. Autonomous Systems Divide The Global Internetwork Into Smaller And More Manageable Networks. Each AS Has Its Own Set Of Rules And Policies And A Number That Distinguishes It From All Other Autonomous Systems.
The Distance Vector Routing Approach Determines The Direction, Or Vector, And Distance To Any Link In An Internetwork.
The Link-State Approach Recreates The Exact Topology Of An Entire Internetwork.
Distance Vector Routing Algorithms Pass Periodic Copies Of A Routing Table From Router To Router. These Regular Updates Between Routers Communicate Topology Changes. The Distance Vector Routing Algorithm Is Also Known As The Bellman-Ford Algorithm.
The Second Basic Algorithm Used For Routing Is The Link-State Algorithm. The Link-State Algorithm Is Also Known As The Dijkstra Algorithm Or As The SPF Algorithm.
Link-State Routing Algorithms Maintain A Complex Database Of Topology Information. The Distance Vector Algorithm Has Non-Specific Information About Distant Networks And No Knowledge Of Distant Routers. A Link-State Routing Algorithm Maintains Full Knowledge Of Distant Routers And How They Interconnect.
DO NOT CONFUSE ROUTING PROTOCOLS WITH ROUTED PROTOCOLS:
Examples Of Routed Protocols Are As Follows:
Internet Protocol (IP)
Internetwork Packet Exchange (IPX)
ALSO KNOW WHAT IS HOST ROUTE:
A Route To A Specific Internetwork Address (Network ID And Host ID). Instead Of Making A Routing Decision Based On Just The Network ID, The Routing Decision Is Based On The Combination Of Network ID And Host ID. Host Routes Allow Intelligent Routing Decisions To Be Made For Each Internetwork Address. Host Routes Are Typically Used To Create Custom Routes To Control Or Optimize Specific Types Of Internetwork Traffic.
EXAMPLES OF IP ROUTING PROTOCOLS INCLUDE THE FOLLOWING:
RIP WAS ORIGINALLY SPECIFIED IN RFC 1058. ITS KEY CHARACTERISTICS INCLUDE THE FOLLOWING:
IGRP IS A PROPRIETARY PROTOCOL DEVELOPED BY CISCO. SOME OF THE IGRP KEY DESIGN CHARACTERISTICS ARE AS FOLLOWS:
OSPF IS A NON-PROPRIETARY LINK-STATE ROUTING PROTOCOL.
EIGRP IS A CISCO PROPRIETARY ENHANCED DISTANCE VECTOR ROUTING PROTOCOL. THE KEY CHARACTERISTICS OF EIGRP ARE AS FOLLOWS:
BORDER GATEWAY PROTOCOL (BGP) IS AN EXTERIOR ROUTING PROTOCOL. THE KEY CHARACTERISTICS OF BGP ARE AS FOLLOWS:
IGP VERSUS EGP:
Interior Routing Protocols Are Designed For Use In A Network That Is Controlled By A Single Organization. The Design Criteria For An Interior Routing Protocol Require It To Find The Best Path Through The Network. In Other Words, The Metric And How That Metric Is Used Is The Most Important Element In An Interior Routing Protocol.
An Exterior Routing Protocol Is Designed For Use Between Two Different Networks That Are Under The Control Of Two Different Organizations. These Are Typically Used Between Isps Or Between A Company And An ISP. For Example, A Company Would Run BGP, An Exterior Routing Protocol, Between One Of Its Routers And A Router Inside An ISP.
IP EXTERIOR GATEWAY PROTOCOLS REQUIRE THE FOLLOWING THREE SETS OF INFORMATION BEFORE ROUTING CAN BEGIN:
An Exterior Routing Protocol Must Isolate Autonomous Systems. Remember, Autonomous Systems Are Managed By Different Administrations. Networks Must Have A Protocol To Communicate Between These Different Systems.
Each AS Must Have A 16-Bit Identification Number, Which Is Assigned By ARIN Or A Provider, To Use Routing Protocols Such As IGRP And EIGRP.
CONCLUSION:
The Goal Of This Article Is To Give An Easy Way To Understand The Cisco – Basic Configuring Static Routes Vs Dynamic Routes, Hope This Article Will Helps Every One (Beginners) Who Are Going To Start Cisco Lab Practice Without Any Doubts. Thank You!
This Article Written Author By: Premakumar Thevathasan. CCNA, CCNP, CCIP, MCSE, MCSA, MCSA - MSG, CIW Security Analyst, CompTIA Certified A+.
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