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I am running into some problems, but I am not sure what is configured wrong. I have a simple network design as follows:

4 routers (connected via serial links) in a square'ish configuration with each router connected to a single switch (via FastEthernet). Here's an ASCII map

     |                             |
     |                             |
     |                             |
     |                             |
     |                             |
     |                             |

The subnets for the serial links are as follows:

The subnets for the Ethernet between the Router and the Switch are as follows:

I'm using Rip v2 for the routing protocol and I have configured each router as follows (in Cisco IOS)

router rip
  version 2

From what I've read, this should result in RIP sending out updates containing multiple (VLSM) routes for the network. However, this is not the case. When inspecting the routes from the bottom left router, I see this:

R4#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set is variably subnetted, 2 subnets, 2 masks
C is directly connected, FastEthernet0/0
R [120/1] via, 00:00:23, Serial0/1
                   [120/1] via, 00:00:12, Serial0/0 is subnetted, 4 subnets
R [120/1] via, 00:00:12, Serial0/0
C is directly connected, Serial0/0
R [120/1] via, 00:00:23, Serial0/1
C is directly connected, Serial0/1

It shows the directly connected subnet as correct, by why is it displaying the rest of the networks as NOT being variable subnetted. This same problem exists on all the routers. Each router is sending an update saying that it has a path to Why are the routers not advertising the correct subnet. Shouldn't RIP v2 support VLSM?

Any help is greatly appreciated. If I am missing something simple, please let me know!

share|improve this question
Do all of the routers have the same most restrictive route (the 10. with the largest prefix)??? Based on what you have posted R4 is directly connected to /20 and for other 10. routes use the two serial ports. Looks right to me. – dbasnett Nov 16 '10 at 19:21
The problems I have however are : R2 can't ping R1, R1 can't ping R3 and R3 can't ping R1. – John Nov 16 '10 at 23:40
up vote 1 down vote accepted

Try entering the command:

router rip
 no auto-summary

From "Cisco IOS Release 12.0 Network Protocols Configuration Guide, Part 1": Configuring RIP

Disable Route Summarization

RIP Version 2 supports automatic route summarization by default. The software summarizes subprefixes to the classful network boundary when crossing classful network boundaries.

If you have disconnected subnets, disable automatic route summarization to advertise the subnets. When route summarization is disabled, the software transmits subnet and host routing information across classful network boundaries.

share|improve this answer
This was absolutely correct. Thank you for the response! This would make sense why the route broadcasts were so ambiguous. – John Nov 18 '10 at 4:11

Wasn't there somesort command for classless routing in IOS?

ip classless or somesort.

Then again I wouldn't recommend to use RIP for this. Your better of using OSPF.

share|improve this answer
I tried that but still am having no luck.. – John Nov 16 '10 at 23:36

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