Classful Auto Summarization – RIPv1

Consider the following network

Both Router TK1 and Router TK2 are running RIPv1. Both routers are configured to
advertise all of their attached networks via RIP. Router TK1 will only see a 10.0.0.0/8 router advertised from by Router TK2. This decision process is based on RIPv1s auto summarization.

Rule 1 – Subnet 134.10.14.5/28
This subnet is dropped because Router TK2 compares the mask to its other subnet 134.10.10.0/24 and they do not match.

For interfaces that are part of the same major network (ie 134.10.0.0/16 in this case) all the component networks should have the same subnet mask. The only change is if the interface is a /32 (or host route).


Rule 2 – Subnet 192.75.1.2/22
This subnet is dropped because this route is a super net (ie /22 mask rather than a bunch of /24). Advertising any network prefix less than its classful major network is not allowed in RIP route summarization.


Rule 3 – Subnet 10.10.10.1/27
This route isn’t part of a major network the router knows about so Rule 1 does not apply. This subnet is also not a super net of a classful network so Rule 2 does not apply. As a result this route is summarize to its classful boundary and send it out to Router Tk1

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