RIP Route Poisoning

RIP Route Poisoning

This is a method to prevent routing loops within computer networks. 
Distance-vector routing protocols in computer networks use route poisoning to indicate to other routers that a route is no longer reachable and should be removed from their routing tables.
Routers consider route advertised with an infinitive metric ( 16 ) to have failed instead of making it down .Here ,for an  example , when network 3 (loopback 3.3.3.3 ) goes down , router 3 starts route poisoning by advertising the metric ( hop count ) of this network as 16 , which indicates  unreachable network. 


R3#debug ip rip

R3(config)#int loopback 0
R3(config-if)#shutdown

R3(config-if)#
*Mar 1 00:04:51.543: %LINK-5-CHANGED: Interface Loopback0, changed state to administratively down
R3(config-if)#
*Mar 1 00:04:51.551: RIP: sending v2 flash update to 224.0.0.9 via FastEthernet0/0 (10.1.13.3)
*Mar 1 00:04:51.555: RIP: build flash update entries
*Mar 1 00:04:51.555: 3.0.0.0/8 via 0.0.0.0, metric 16, tag 0
R3(config-if)#
*Mar 1 00:04:52.543: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to down
R3(config-if)#
*Mar 1 00:04:53.651: RIP: received v2 update from 10.1.13.2 on FastEthernet0/0
*Mar 1 00:04:53.655: 3.0.0.0/8 via 0.0.0.0 in 16 hops (inaccessible)
R3(config-if)#
*Mar 1 00:04:55.895: RIP: received v2 update from 10.1.13.2 on FastEthernet0/0
*Mar 1 00:04:55.899: 1.1.1.0/24 via 0.0.0.0 in 2 hops
*Mar 1 00:04:55.903: 2.2.2.0/24 via 0.0.0.0 in 1 hops
*Mar 1 00:04:55.903: 3.0.0.0/8 via 0.0.0.0 in 16 hops (inaccessible)
*Mar 1 00:04:55.907: 10.1.12.0/24 via 0.0.0.0 in 1 hops



R2#
*Mar 1 00:04:52.895: RIP: received v2 update from 10.1.13.3 on FastEthernet1/0
*Mar 1 00:04:52.895: 3.0.0.0/8 via 0.0.0.0 in 16 hops (inaccessible)
R2#
*Mar 1 00:04:54.899: RIP: sending v2 flash update to 224.0.0.9 via Loopback0 (2.2.2.2)
*Mar 1 00:04:54.903: RIP: build flash update entries
*Mar 1 00:04:54.903: 3.0.0.0/8 via 0.0.0.0, metric 16, tag 0
*Mar 1 00:04:54.907: RIP: sending v2 flash update to 224.0.0.9 via FastEthernet0/0 (10.1.12.2)
*Mar 1 00:04:54.911: RIP: build flash update entries
*Mar 1 00:04:54.911: 3.0.0.0/8 via 0.0.0.0, metric 16, tag 0
*Mar 1 00:04:54.915: RIP: sending v2 flash update to 224.0.0.9 via FastEthernet1/0 (10.1.13.2)
*Mar 1 00:04:54.915: RIP: build flash update entries
*Mar 1 00:04:54.919: 3.0.0.0/8 via 0.0.0.0, metric 16, tag 0
R2#
*Mar 1 00:04:54.931: RIP: ignored v2 packet from 2.2.2.2 (sourced from one of our addresses)
R2#
*Mar 1 00:04:57.019: RIP: received v2 update from 10.1.12.1 on FastEthernet0/0
*Mar 1 00:04:57.023: 3.0.0.0/8 via 0.0.0.0 in 16 hops (inaccessible)
*Mar 1 00:04:57.167: RIP: sending v2 update to 224.0.0.9 via FastEthernet1/0 (10.1.13.2)
*Mar 1 00:04:57.171: RIP: build update entries
*Mar 1 00:04:57.171: 1.1.1.0/24 via 0.0.0.0, metric 2, tag 0
*Mar 1 00:04:57.175: 2.2.2.0/24 via 0.0.0.0, metric 1, tag 0
*Mar 1 00:04:57.175: 3.0.0.0/8 via 0.0.0.0, metric 16, tag 0
*Mar 1 00:04:57.179: 10.1.12.0/24 via 0.0.0.0, metric 1, tag 0