RIP protocol

Unanswered Question
Apr 26th, 2007

Thank you all for your information ...

i have this network topology and configured using RIP v1 in my virtual lab ...

by default it shouldn't work using RIP v1 but it works well..we have different subnet masks....

so why it works....

I have this problem too.
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mohammedmahmoud Fri, 04/27/2007 - 00:41

Hi there,

This is called discontigous network, normally R1 should advertise (auto-summary), and R2 will drop the route since it has learned a subnet of the same major network from a connected interface, please issue a debug ip rip to trace the operation.

Please refer to these documents:

Behavior of RIP and IGRP When Sending and Receiving Updates

Why Doesn't RIP or IGRP Support Discontiguous Networks?

HTH, please rate if it does help,

Mohammed Mahmoud.

alwahidi22 Fri, 04/27/2007 - 01:04

thank you Mohammed for your response , but 1) i want to know that i can use different subnet mask lengths within RIP networks , if yes why we say that RIP is clasfull protocol

2) discontigous network you mean here that we connect for example two networks(class A) for example using network( class B ) or using different network portion ( class A )

Jon Marshall Fri, 04/27/2007 - 01:37


You can use different subnet masks per major subnet ie. you could use the following


You cannot use different subnets within the same major network ie.

This is because RIP does not exhange the subnet mask in it's routing updates.

Discontiguous means exactly what you say and what you have done in your lab.



alwahidi22 Fri, 04/27/2007 - 01:57

thank you jon

i appreciated your response and it was very helpful for me , so 1)the discontiguous network doesn't work with RIP ?

...2)is the following topology Discontiguous network ?

3)is the following topology work with RIP v1?

by the way this is one of the topology that used in one of cisco books

Jon Marshall Fri, 04/27/2007 - 02:08


No this is not a discontiguous example.

The major network numbers are

So you do not have a major network that is split by another major network.

Yes the above topology should work with RIPv1 for the reasons stated above.



mohammedmahmoud Fri, 04/27/2007 - 03:14

Hi there,

You're last example is not a discontigous network (no major network overlap), but your original post was a discontigous network, and RIPv1 doesn't support discontigous networks, as it never sends the subnet mask with the routes, please refer to the documents i've send you.


Mohammed Mahmoud.

alwahidi22 Fri, 04/27/2007 - 03:54

does this topology work with RIP V1

Jon Marshall Fri, 04/27/2007 - 04:12


No it shouldn't because here you do have a discontiguous major network ie.

See Mohmammed's links for more details.



mohammedmahmoud Fri, 04/27/2007 - 04:15


Just as Jon has said, it shouldn't work as its a discontigous network, and referring to the link both routers will drop the routes exchanged since they match the major boundary.


Mohammed Mahmoud.

alwahidi22 Fri, 04/27/2007 - 04:37

Thank you Mohammad , i appreciated your ideas and i hope to be friends

mohammedmahmoud Fri, 04/27/2007 - 04:42

Hi Ibrahim,

You are always welcomed, and i'll be glade to have you as a friend.


Mohammed Mahmoud.

alwahidi22 Fri, 04/27/2007 - 04:35

Thank you jon , i have understand all the ideas you talk

thank you very much


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