RIP Troubleshooting.

1.Version difference as Version 1 advertises only classful networks.
   Version 1 auto summarizes. This will be a problems in classless
   discontigious networks
2.Split Horizon.
    Networks that are learned on an interface are not advertised out
    of the same interface.
3.Route poisoning ,watch for Metric 16 considered as infinite by RIP
   in the debug command output.
4.Subnet Mask.
5.Configuration.Check the Network command.
6.Passive interface.
    An interface that has been configured as passive will not send any 
    RIP updates.
7. Max hop count: When the hop count is 16, the network is considered
    unreachable.
8. ACL filtering traffic.
                  ex an ACL  filtering 224.10.11.0/17
                  RIPv2 uses the Multicast 224.0.0.9 = All RIPv2 routers
                  RIPv1 just sends everything to everyone.
9.Authentication: Both RIP routers should have the same authentication
   parameters.

10.Timers

Commands :
show ip protocols
show ip route rip
debug ip rip
show ip rip database