Solved: RIP - Advertising Classless/CIDR

dannydd97 · ‎09-29-2012

Hi everyone,

I was doing a basic config and wanted confirmation by you guys:

R1(config)#router rip

R1(config-router)#version 2

R1(config-router)#net 1.1.1.0

R1(config-router)#net 11.11.11.0

R1(config-router)#net 12.12.12.0

R1(config-router)#no auto-summary

I want to advertise the /24 of the above subnets.

When I do a sh run, I see the below:

router rip

version 2

network 1.0.0.0

network 11.0.0.0

network 12.0.0.0

no auto-summary

Each subnet is being advertised as /8. I tried configuring ip classless but it made no difference.

Any idea why it's being advertised as /8 and not /24?

Thanks

Jon Marshall · ‎09-29-2012

Your "sh run" output does not mean they are being advertised as classful. The network config under RIP always uses classful addressing but that does not mean that is what is being advertised. So when you enter "1.1.1.0" that is changed under the router RIP config to the classful network but if you have an interface configured in the 1.1.1.x/24 subnet then that subnet should be advertised.

As you say you need "no auto-summary" turned on.

*** Edit - the way to test this is to connect another router to this one, run RIPv2 on that as well and then look at the routing table.

*** Edit 2 - note also that the config you see under router rip is not the networks you are going to advertise. The network command under RIP/EIGRP/OSPF is used to tell the router which interfaces to run the routing protocol on, it is not like the network command in BGP which is used to advertise a specific network.

Jon

View solution in original post

Jon Marshall · ‎09-29-2012

Your "sh run" output does not mean they are being advertised as classful. The network config under RIP always uses classful addressing but that does not mean that is what is being advertised. So when you enter "1.1.1.0" that is changed under the router RIP config to the classful network but if you have an interface configured in the 1.1.1.x/24 subnet then that subnet should be advertised.

As you say you need "no auto-summary" turned on.

*** Edit - the way to test this is to connect another router to this one, run RIPv2 on that as well and then look at the routing table.

*** Edit 2 - note also that the config you see under router rip is not the networks you are going to advertise. The network command under RIP/EIGRP/OSPF is used to tell the router which interfaces to run the routing protocol on, it is not like the network command in BGP which is used to advertise a specific network.

Jon

dannydd97 · ‎09-29-2012

Your absolutely right, thanks a lot and appreciate the response.

I just played around with some redistribution and your right, the routes are showing /24. I was just curious why it was showing /8 in the sh run.

1.0.0.0/24 is subnetted, 1 subnets

D EX 1.1.1.0 [170/1709312] via 34.34.34.1, 00:03:06, FastEthernet0/0

11.0.0.0/24 is subnetted, 1 subnets

D EX 11.11.11.0 [170/1709312] via 34.34.34.1, 00:05:32, FastEthernet0/0

12.0.0.0/24 is subnetted, 1 subnets

D EX 12.12.12.0 [170/1709312] via 34.34.34.1, 00:05:32, FastEthernet0/0

Thanks for the clarification