Distance Vector Routing Protocols Module 7 Distance Vector Routing Protocols

RECALL: Dynamic Routing Dynamic routing refers to the process of allowing the router to determine the path to the destination. avoid the time-consuming process of configuring static routes Routing protocols enable dynamic routing where multiple paths to the same destination exist.

Distance Vector Routing Updates Routing table updates occur: _______________________________ __________________________________________________________________ Recall: Router to send its entire routing table to each of its _______ ___________________________ Contents include: information about the _______________________________

Routing Loop Problem TALK ABOUT EXAMPLE Just before the failure of Network 1, all routers have consistent knowledge and correct routing tables. The network is said to have converged. Assume for the remainder of this example that Router C's preferred path to Network 1 is by way of Router B, and the distance from Router C to Network 1 is 3. When Network 1 fails, Router E sends an update to Router A. Router A stops routing packets to Network 1, but Routers B, C, and D continue to do so because they have not yet been informed of the failure. When Router A sends out its update, Routers B and D stop routing to Network 1. However, Router C has not received an update. To Router C, Network 1 is still reachable via Router B. Now Router C sends a periodic update to Router D, indicating a path to Network 1 by way of Router B. Router D changes its routing table to reflect this good, but incorrect, information, and propagates the information to Router A. Router A propagates the information to Routers B and E, and so on. Any packet destined for Network 1 will now loop from Router C to B to A to D and back to again to C.

Counting to Infinity __________ ____________________________________________________________________________________ __________________ allows a routing loop and the count to infinity problems to exist.

Solution (to count to infinity) Protocols define -__________________ ______________________________. When metric exceeds its maximum allowed value, _______________________________ ___________________________________ Examples: RIP- max of 15 hop counts

Another Solution (Split Horizon) A routing update regarding a certain network, __________________________ ____________________________________________________________________.

Split Horizon Split-horizon attempts to avoid this situation. If a routing update about Network 1 arrives from Router A, Router B or Router D cannot send information about Network 1 back to Router A. Split-horizon thus reduces incorrect routing information and reduces routing overhead

Another Solution (Route Poisoning)

Route Poisoning Causes an ____________________ _______________ for a failed route The router that receives the poison update will then _______________ _____________________, called a poison reverse. This ensures all routes on the segment have received the poisoned route information.

Triggered Updates ______________________________________________________________________________________ Instead of waiting the protocol’s default time to send the update

Another Solution (Hold-down timers) When a router receives an update from a neighbor indicating a network is down, _______________________________ ________________________________________________________________ Only under certain circumstances is that hold-down timer removed Hold-down timer allows time for _______________________________

Holddown Timers

Enabling RIP and IGRP In Global configuation mode ______________________________________ In router config mode ____________________________________________________

RIP specifics It is a distance-vector routing protocol. ____________________________________________________________________________ Max. _______________________________ After that destination assumed unreachable By default, ___________________________ ___________________________________ Ex command: Router(config)# _____________

Rip cont… When a router receives a routing update that contains a new or changed entry, __________ ________________________________________________________________________ Can maintain _________________________ ____________________________ Can be configured on serial interfaces to _____ __________________________________________________________________________ ip rip triggered command

RIP Configuration

RIP and classless If “ip classless” is disabled and one part of a major network is known, but the ______ __________________________________________________________________ If a default route is configured, ______ _______________________________ Configuring ip classless on a router will solve this problem therefore… ip classless command is enabled by default in Cisco IOS v. 11.3 and later

RIP commands Know when and how to use the RIP commands such as _______________________ Default ___________________ can be configured for _________________ _________________________________________________________________________________ ________________________ The ideal setting would be to set the timer just __________________________________________________________________________________

Example of Classless routing

IGRP specifics ___________________________________ routing protocol Scalable to larger networks By default, routing updates are _______________ _______________________________________ ______________________________ are the two characteristics used to generate the metric, ___________________________ _______________ other characteristics which can be set Example global command router(config)# router igrp 2 router(config-router)# network 12.0.0.0 Autonomous System number - required

General Commands Verify and troubleshoot RIP and IGRP configurations with the following commands… Show ip route Show ip protocol show interface interface show ip interface interface show running-config debug ip rip

Command detail show ip interfaces

Another SHOW command show ip protocol Associated with the ______________________

Another SHOW command cont… show ip route Essential for troubleshooting networks

Lastly… Debug commands Powerful but ___________________________ __________________________________ Allow _________________________________ Basically another "show" command Example: “debug ip rip “ command displays RIP routing updates as they are sent and received (in real time) Use “no debug ip rip” or “no debug all” to turn debugging off

Labs to complete Lab 7-1 Configuring RIP Lab 7-2 Troubleshooting RIP Lab 7-3 Preventing Routing Updates Through an Interface Lab 7-4 Load Balancing Across Multiple Paths Optional Lab 7-5 Configuring Interior Gateway Routing Protocol