Summarization!!

Hey guys i'm not clearing the air on this topic. So classless routing protocols support auto-summary and classful routing protocols too allow auto-summary with the difference being that we can turn off auto-summary on classless routing protocols . So when we have discontiguous networks we disable autosummary on classless routing protocols but we can't on classful routing protocols . So this means that classful routing protocols chances of using is almost nil ! Right ? But in the vast mistic world of internet their are bound to be discontiguous networks , so the use of auto-summary in reducing routing tables is not such a great hit out their afterall ?

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Comments

tomaifauchai

You always want to turn off "Auto" stuff most of the time and do manual summarization

For Classful the following two rules govern RIPv1 updates:

If a routing update and the interface on which it is received belong to the same major network, the subnet mask of the interface is applied to the network in the routing update.
If a routing update and the interface on which it is received belong to different major networks, the classful subnet mask of the network is applied to the network in the routing update.

sKGP

tomaifauchai wrote: »

You always want to turn off "Auto" stuff most of the time and do manual summarization

For Classful the following two rules govern RIPv1 updates:
If a routing update and the interface on which it is received belong to the same major network, the subnet mask of the interface is applied to the network in the routing update.

If a routing update and the interface on which it is received belong to different major networks, the classful subnet mask of the network is applied to the network in the routing update.

I didn't get you about the classfull part could you elaborate . And if manual summary is done more as you say isn't it just gonna be too much large networks ?

thanks in advance

tomaifauchai

Example 1
192.168.1.0/30

R1----192.168.1.4/30----R2

192.168.1.8/30

On R1, your routing table would be as follow, even if it's RIPV1 configured on the 3 routers

C 192.168.1.0/30
C 192.168.1.4/30
R 192.168.1.8/30

Because 192.168.1.8/30 is in the same Classful network (192.168.1.0/24) than the IP on the R1 interface where it receive the update from R2
(took me a while to understand too...don't worry)

( R1(apply mask from the interface) <

R2 )

A situation where it won't work is
192.168.2.0/30

R1----192.168.1.4/30----R2

192.168.2.8/30

With such a setup on RipV1, you're doomed because R1/R2 apply classful mask because the received updates IS NOT from the same classful network and there's already a better Connected route for network 192.168.2.0.
If you have Packet tracker or GNS3, you should try both example on Ripv1 and Ripv2, with no auto-summary configured