RIP v2 in nutshell

1, RIP does not form adjacency for each other,  nor do they use hello protocol. It just send out update to the mulitcast destination ip 224.0.0.9 with UDP protocol port 520. RIPv2 router can also configured to use the 255.255.255.255 broadcast ip address, but this is not commonly done.

RIP can also send unicast update, when “neighbor ip-address” command is configured, identifys a neighbor to which unicast RIP updates will be sent.

RIPv2 has only 2 types of messages: requests and Responses

Update interval is 30 seconds by default, update will be full update, when routes change, update will be triggered as well.

2, RIPv2 convergence and loop prevention is realized by the following functions:

  • Counting to Infinity(16)
  • Split Horizon(should not be enabled in point-to-mulitpoint segment)
  • Route Poisoning
  • Split Horizon with Poisoned Reverse
  • Triggered update
  • Update time (30 secs by default)
  • Invalid after time (180 secs by default)
  • Holddown timer (180 secs by default)
  • Flushed after timer (240 secs by default)

When a router has one interface shutdown, router will flush the poisoned routes to all of other interfaces, the update will been sent immediately. When a router has a link down, after “Invalid after time”, the route will be set as invalid, holddown timer starts, after 60 secs, route will be flushed and holddown timer reset, the route change will trigger update as in the first scenario.

3, Routes can be filtered in both “in” and “out” direction by using distribute-list

4, RIPng for IPv6

5, “clear ip route *” command will clear the routing table entry and with RIP, sends RIP requests, quickly rebuilding the routing table

6, RIP version 2 support classless routes ads, but in order to advertise classless route, command “no auto summary” need to be configured.