Sunday, February 19, 2006

 

RIP version mismatch. (Question #17)

Consider a simple three router network such as the following

Router1 ---- Router2 ---- Router3

Assume that the routers are all connected to each other over ethernet interfaces and that the interfaces are up and the neighbors can ping each other. The subnet on the left is 10.10.10.0/24 and that on the right is 20.20.20.0/24

Here is the relevant snippet relating to the configuration of the RIP routing protocol on the three routers

Router1

router rip
network 10.0.0.0



Router2

router rip
version 2
network 10.0.0.0
network 20.0.0.0



Router3

router rip
network 20.0.0.0



Note that the router in the middle is running RIPv2 while the other two routers are running RIPv1. Will the version mismatch cause a problem with routing in this network? Can Router3 ping interfaces on Router1 if there is no other routing related configuration on the routers other than the RIP configuration shown above?

Comments:
RFC 1723:
4. Compatibility
RFC 1058 showed considerable forethought in its specification of the handling of version numbers. It specifies that RIP messages of version 0 are to be discarded, that RIP messages of version 1 are to be discarded if any Must Be Zero (MBZ) field is non-zero, and that RIP messages of any version greater than 1 should not be discarded simply because an MBZ field contains a value other than zero. This means that the new version of RIP is totally backwards compatible with existing RIP implementations which adhere to this part of the specification.


So we can hope that this configuration of RIP1/2 should work if Cisco follows RFC.
 
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