RIP Poison Reverse

When a router receives a route poisoning, it sends an update back to the router from which it received the route poisoning, this is called poison reverse.Always thank your buddy for covering your black.

Here , an example , router 2 receives a route poisoning of network 3 from router 3 then router 2 will send an update back to router 3 which breaks the split horizon rule with the same poisoned hop count of 16.This ensures all routers in the domain receive the poisoned route update.

All routers have loopback address and need to run RIP v2 

R3#debug ip rip

RIP protocol debugging is on

R3(config)#int loopback 0

R3(config-if)#shutdown

R3(config-if)#

*Mar 1 00:06:00.875: %LINK-5-CHANGED: Interface Loopback0, changed state to administratively down

R3(config-if)#

*Mar 1 00:06:00.887: RIP: sending v2 flash update to 224.0.0.9 via FastEthernet0/0 (10.1.13.3)

*Mar 1 00:06:00.891: RIP: build flash update entries

*Mar 1 00:06:00.891: 3.3.3.0/24 via 0.0.0.0, metric 16, tag 0

*Mar 1 00:06:01.659: RIP: sending v2 update to 224.0.0.9 via FastEthernet0/0 (10.1.13.3)

*Mar 1 00:06:01.663: RIP: build update entries

*Mar 1 00:06:01.663: 3.3.3.0/24 via 0.0.0.0, metric 16, tag 0

R3(config-if)#

*Mar 1 00:06:01.875: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to down

R3(config-if)#

*Mar 1 00:06:03.043: RIP: received v2 update from 10.1.13.2 on FastEthernet0/0

*Mar 1 00:06:03.047: 3.3.3.0/24  via 0.0.0.0 in 16 hops (inaccessible)

R3(config-if)#

*Mar 1 00:06:13.735: RIP: received v2 update from 10.1.13.2 on FastEthernet0/0

*Mar 1 00:06:13.739: 1.1.1.0/24 via 0.0.0.0 in 2 hops

*Mar 1 00:06:13.739: 2.2.2.0/24 via 0.0.0.0 in 1 hops

*Mar 1 00:06:13.743: 3.3.3.0/24 via 0.0.0.0 in 16 hops (inaccessible)

*Mar 1 00:06:13.747: 10.1.12.0/24 via 0.0.0.0 in 1 hops

R2#

*Mar  1 00:12:35.179: RIP: received v2 update from 10.1.13.3 on FastEthernet1/0

*Mar  1 00:12:35.179:      3.3.3.0/24via 0.0.0.0 in 16 hops  (inaccessible)

R2#

*Mar  1 00:12:40.163: RIP: sending v2 update to 224.0.0.9 via FastEthernet1/0 (10.1.13.2)

*Mar  1 00:12:40.163: RIP: build update entries

*Mar  1 00:12:40.163:   1.1.1.0/24 via 0.0.0.0, metric 2, tag 0

*Mar  1 00:12:40.167:   2.2.2.0/24 via 0.0.0.0, metric 1, tag 0

*Mar  1 00:12:40.167:   3.3.3.0/24 via 0.0.0.0, metric 16, tag 0

*Mar  1 00:12:40.171:   10.1.12.0/24 via 0.0.0.0, metric 1, tag 0

R2#debug ip rip database

RIP database events debugging is on

Flash update of Link goes down

R2#

*Mar  1 00:02:41.483: RIP-DB: Remove 3.3.3.0/24, (metric 4294967295) via 10.1.13.3, FastEthernet1/0

*Mar  1 00:02:41.487: RIP-DB: adding 0.0.0.0/0 (metric 4294967295) via 0.0.0.0 on Null0 to RIP database

R2#

*Mar  1 00:02:59.955: RIP-DB: network_update with 1.1.1.0/24 succeeds

*Mar  1 00:02:59.959: RIP-DB: adding 1.1.1.0/24 (metric 1) via 10.1.12.1 on FastEthernet0/0 to RIP database

Flash update of link comes back to Up

R2#

*Mar  1 00:30:55.791: RIP-DB: network_update with 3.0.0.0/8 succeeds

*Mar  1 00:30:55.795: RIP-DB: adding 3.3.3.0/24 (metric 1) via 10.1.13.3 on FastEthernet1/0 to RIP database

*Mar  1 00:30:55.799: RIP-DB: add 3.3.3.0/24 (metric 1) via 10.1.13.3 on FastEthernet1/0