Configuring RIP

[admin_2]

In preparation for my CCNA exam I found a test question that is a bit confusing. The config is as follows:

Note: the routing protocol is rip

(config) int e0

(config-if)ip address 192.168.81.33 255.255.255.224

config-if)no shutdown

(config) int s1

config-if)ip address 192.168.81.65 255.255.255.224

config-if)no shutdown

The question never shows the network statements.

Since rip is a classfull routing protocol I would think that the 255.255.255.224 subnet mask is pointless.

I will not advertise that subnet right?

So since it wont advertise that subnet the subnet mask on both interfaces should be 255.255.255.0

If the routing protocol was eigrp,ospf, or ripv2 you would be okay with the

255.255.255.224 subnet mask. The above routing protocols support vlsm.

Am I on the right track or am I missing somthing?

Thank you in advance.

[sundar.palaniappan]

You are partly correct. RIP v1 doesn't net send subnet mask info in it's updates. RIP v1 doesn't support VLSM. But, it does support fixed length subnet mask.

Take a look at this example. In the below scenario, both R1 & R2 run RIP v1 on all the interfaces. Since R1's ethernet and s0 are configured with the same subnet mask it would send a routing update for 192.168.1.0. R2 knowing the subnet mask is 255.255.255.224 on it's s0 interface it would apply the same subnet mask for the 192.168.1.0 it learnt from R1.

R1:

int e0

ip add 192.168.1.1 255.255.255.224

int s0

ip add 192.168.2.1 255.255.255.224

R2:

int s0

ip add 192.168.2.2 255.255.255.224

HTH

Sundar

[#3]

So in this example, just maintain the same subnet mask on your interfaces and you would be okay?

Your adverised routes would still be classfull but you would still communicate with no problems between r1:ints0 and r2:ints0.....they are on the same subnet.

Makes sense now that you explained it.

Thank you for your help!

Don

[sundar.palaniappan]

Yes, your understanding is correct:)