RIPv2

RIPv2, isn’t that hard at all.
There are a few enhancements from RIPv1:

• Authentication: clear text (by default) or MD5
• Subnet masks: RIPv2 is classless
• Next-Hop IP address: to avoid routing loops (used in networks with multiple routing protocols)
• Updates are send by multicast, to IP 224.0.0.9

 RIPv2 is compatible with RIPv1. Switching between accepting/sending v1 or v2 updates is possible with the following interface commands:

Router(config-if)#ip rip send version 1
Router(config-if)#ip rip receive version 1
Router(config-if)#ip rip send version 1 2

By default, Cisco IOS rejects the configuration of a subnet with all 0’s even if a classless routing protocol is being used. 172.16.0.0/16 is the network, 172.16.0.0/24 is  a all-0’s network. To override this, the following command is used (enabled by default):

Router(config)#ip subnet-zero

Limitations

Limitations of RIPv2 are:

• Lack of alternative routes
  • The router has to wait untill the next routing update period for receiving a new route after the last one was faulty.
• Couting to infinity
  • To solve this, RIP relies on split horizon, route poisoning and holddown mechanisms
• Max 15 hops (hopcount)

Authentication

MD5 configuration of authentication in the RIP process should always be done with a key-chain even if there’s only 1 key configured!

Router(config)#key chain ripchain
Router(config-keychain)#key 1
Router(config-keychain-key)#key-string ripsecret
Router(config-keychain-key)#interface fastethernet 0/0
Router(config-if)#ip rip authentication key-chain ripchain
router(config-if)#ip rip authentication mode md5

 
Auto-summary
On last impartant part: auto summary. This is enabled by default. To allow RIP to advertise routes with subnet, use the following router-RIP command:

Router(config)#router rip
Router(config-router)#version 2
Router(config-router)#no auto-summary