What does the 'network w.x.y.z' RIPv2 command specify?

Question

I'm studying networking protocols, and am starting with RIP.

When configuring RIPv2, I see 2 pieces of information you need to relay to the router:

1. Which interfaces to advertise RIP updates on
2. Which subnets to advertise about

As far as I can tell, this seems to be jumbled into one network w.x.y.z command, which is a bit confusing. What exactly are you telling the router when you specify something like network 192.168.0.0?

Are you saying that you want to BOTH:

• enable RIP on any interfaces that have an IP that falls within that Class C network; and
• advertise about any subnets the router knows about that falls within that network?

In this example:

According to some online sources, I would configure Router0 with both network 192.168.0.0 and network 192.168.5.0, which does work, and seems to suggest that the network command does indeed do both (specify the interfaces for rip to run on, and which interfaces to advertise about) at the same time. Is this correct?

Answer 1

The network statement will tell RIP which interfaces to include in RIP, and RIP will determine what networks to advertise from the interfaces included in RIP.

If you want to advertise the 192.168.0.0 network to Router1 from Router0, then, yes, you will use a network statement to do that. That will also cause RIP to send updates to interface F0/1, which is probably undesirable because there is no neighbor router on that network. You can use the passive-interface command to advertise the network on that interface without sending updates out that interface.

For example:

router rip
 version 2
 no auto-summary
 network 192.168.0.0
 network 192.168.5.0
 passive-interface FastEthernet0/1
!

The above example will advertise the 192.168.0.0/24 network from Router0 to Router1, but it will not send RIP updates to the user network on F0/1.