RIP Summarization

Lessons learned:

Rip Summarization –

Interface level | ip summary-address rip

At least one subnet must be in the rip database

Cannot summarize past the major network boundary
-workaround with “redistribute static”

-----------------------------------------------------------------------------

In order to summarize the aggregate at least one subnet must be in the RIP database. Ex: if we have 2 x /25 networks and we’re trying to generate a /24 summary, at least one of those networks would have to be in the database to begin with. We will need a corresponding network statement or another form of redistribution.  We cannot summarize past the major boundary.

EX: If we have 4 class C networks.  We could summarize the following to 192.168.0.0./22
192.168.0.0 /24
192.168.1.0 /24
192.168.2.0 /24
192.168.3.0 /24

The problem with RIP is that we cannot go past the major network boundary. The problem is that all these addresses are major class C networks or /24.

RIP will not allow this with summarization by itself. We could potentially do a static route to Null0 and redistribute these in. RIP does support the advertisement of arbitrary networks but within RIP there is a check that will not allow you to go past the major network boundary.

EX: if we wanted to summarize the networks

10.10.7.0 /24 and 10.10.9.0 /24 – we can summarize these routes with a /20

So the summary address would be 10.10.0.0 /20

To configure the routers.
on the interface you want to summarize -
# int FA0/0
# ip summary-address rip 10.10.0.0 255.255.240.0

We can verify this after by showing the route and looking at the route entry.
#sh ip route 10.10.7.10 – IP of host in the summary range.
Should show – routing entry for the new summary address.

Another workaround – we should extend the summary to a /8 and route the traffic to Null0. That way we have a placeholder for the network.  We can then go under the Rip process and redistribute static.

Router rip
redistribute static