Question/confusion about the network command for RIP

marcel2271

After reading both Sybex 5th edition (Todd Lammle) and the ICND Exam Certification Guide (Wendell Odom) I got confused about the network command used for RIP configuration. I believe Sybex is wrong about RIP configuration.
In Sybex the network command is described as follows: "it tells the routing protocol which networks to advertise". It doesn't mention that the interface which matches the network command will participate in sending/receiving RIP routing updates (see Sybex page 253). In the ICND Certification Guide it is mentioned.

Then on page 257 (Sybex) there is an example using the passive-interface command which will stop RIP updates from being propagated out serial interface 0. But that particular interface's network (192.168.20.0) is not even used in the network command, so why even bother using the passive-interface command for that interface?
And finally there is an example on page 268 which shows the output of "sh ip protocols" and "sh ip interface brief". The example shows that serial 0/0 and 0/1 send and receive RIP updates. Only network 10.0.0.0 is used in the network command. This is only matching interface s0/0, but interface s0/1 is off 192.168.11.0!! So how can RIP send and receive updates out s0/1?
So according Sybex ALL interfaces will always participate in sending/receiving RIP updates (at least this is my conclusion after reading the chapter).

Can somebody confirm that Sybex is wrong here?

marcel2271

I did some more investigation with Boson NetSim but this is confusing me even more

I created a very simple network:


H2

---

|
H1 --- R1 --- R2 --- R3 --- H3


H1: 172.16.1.130/26
R1 left: 172.16.1.129/26
R1 right: 172.16.1.66/26
R2 left: 172.16.1.65/26
R2 to H2: 192.168.1.17/28
H2: 192.168.1.18/28
R2 right: 192.168.1.1/28
R3 left: 192.168.1.2/28
R3 right: 192.168.1.33/28
H3: 192.168.1.34/28

Then I only configured RIP on R2 and R3 as follows:

R2(config)#router rip
R2(config-router)#network 192.168.1.0

R3(config)#router rip
R3(config-router)#network 192.168.1.0

As expected R3 only learns a route to subnet 192.168.1.16/28. And R2 only learns a route to subnet 192.168.1.32. Then I switch on debug ip rip on R2. As I expected no RIP updates are being sent via the interface to R1 (it's in network 172.16.0.0).
However, when I issue the command "sh ip protocols" I see the following output:

<cut for brevity>
Default version control: send version 1, receive any version
Interface Send Recv Key-chain
Serial0 1 1 2
Serial1 1 1 2
Ethernet0 1 1 2
Routing for Networks:
192.168.1.0
Routing Information Sources:
192.168.1.2 120 00:00:06
Distance: (default is 120)

As you can see above it mentiones 3 interfaces but I only expected to see 2 interfaces. Interface Serial1 is the one I used to connect R2 to R1 and this interface is off network 172.16.0.0!!!

Who can help me explain this?

vvii

Doesn't rip have to be in the same subnet, it seems like in your example, it show that its /26 and /28 for the mask

marcel2271

For a classful routing protocol like RIP there should only be one mask for for each classful network. And that's what I did: I used the mask /26 for classful network 172.16.0.0 and mask /28 for classful network 192.168.1.0.
Of course I didn't use VLSM.