Ripv1

[kishorecisco]

Hi I have two router R1 and R2. My R1 network address are

R1                                                            R2

Fa0/0                                                        Fa0/0

172.16.100.0/24                                         172.16.200.0/24

S0/0                                                          S0/0

172.16.10.1/24                                            172.16.10.2/24

I'm using Ripv1 as my routing protocol. What will be in my R2's routing table. Please explain.

[John Blakley]

Believe it or not, I believe you're only going to see your local routes. The problem is that you're going to be advertising a classful network of 172.16.0.0/16. The mask isn't sent to the neighbor.

HTH,

John

[Richard Burts]

I can not read the file that you attached. So I do not know what is in it. But based on the description in your post I do not agree with John. Your post describes a network that has 3 subnets within the class B 172.16.0.0 network. And the subnets are the same size. Assuming that interfaces are correctly configured and that the configuration for rip includes the network statement for 172.16.0.0 then I would expect that 172.16.100.0 should be in the routing table for R2 and that 172.16.200.0 shhould be in the routing table for R1.

HTH

Rick

[kishorecisco]

Thank  you sir for the reply. But since ripv1 does not bother about subnet mask how can it show those networks.

[Richard Burts]

There are several things to be aware of about RIPv1;

- ripv1 uses auto summary. So when a subnet is advertised out an interface that is a different network it will automatically be summarized. So if 172.16.100.0 were being advertised out an interface with 192.168.10.0 then it would be summarized. But in your description 172.16.100.0 is advertised over 172.16.10.0. So it would not be summarized and 172.16.100.0 would be advertised.

- ripv1 requires that all subnets within a network use the same subnet mask. So if 172.16.100.0/24 were advertised over an interface with /30 mask then it would not be advertised. But in your description all subnets use /24 mask. So the subnets would be advertised.

Perhaps it would help to have a short discussion about not advertising masks. If a network had some subnets with mask of /24 and some masks of /30 then it would need to advertise the mask for the subnet to be properly recognized.  But ripv1 does not advertise the mask and could not advertise this. Ripv1 requires that all subnets use the same mask. So if R2 receives an advertisement of 172.16.100.0 over an interface that has mask of /24 then R2 can safely assume that the mask for 172.16.100.0 is /24. Since this is the case in your network the subnet will be advertised.

HTH

Rick

[John Blakley]

Rick,

What you said made sense, and after rereading my post I have to retract. I labbed it up and noticed that I would get the internal address, but then I changed the mask on one of my loopbacks and lost the address because now it was being summarized. Now it makes total sense...

Thanks!

John

[Richard Burts]

John

I am glad that my explanation helped clarify it for you.

HTH

Rick

Sent from Cisco Technical Support iPhone App

[cadet alain]

Hi,

R1 has 172.16.100.0 to advertise so it will compare the major network of this route with the one from the update sourcing interface(s0/0).

Here they are the same( 172.16.0.0/16) so it won't autosummarize.

Now it compares subnet mask of the route with the one from the update sourcing interface(s0/0) and it finds that they are the same so it will advertise this route( 172.16.100.0 with no subnet mask as it is rip v1).

Now R2 receives this update and it sees it is part of the same major network as it receiving interface so it will apply its receiving interface subnet mask to the update.

The same process goes for updates sent from R2 to R1.

Regards.

Alain

Don't forget to rate helpful posts.

[kishorecisco]

thank you

[kishorecisco]

Thank you

[cadet alain · Accepted solution]

Hi,

if we answered your question then would you mind marking the thread as solved and give ratings to whom you considered gave you the informations you needed.

Regards.

Alain

Don't forget to rate helpful posts.