auto-summarization: classful vs classless routing protocols

Posted by yorble on Server Fault See other posts from Server Fault or by yorble
Published on 2012-10-14T20:49:59Z Indexed on 2012/10/14 21:39 UTC
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ip-routing

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rip

Suppose a router R1 is directly connected to the following subnets:

10.1.0.0/24

10.1.1.0/24

10.1.2.0/24

10.1.3.0/24

If it is running RIPv1, it will advertise:

"i have the network 10.0.0.0" (implicitly understood by receiving RIPv1 routers as 10.0.0.0/8 because the protocol is classful)

but suppose we changed the routing protocol to RIPv2 and turned ON auto-summarization. Would it behave in the same way? Would it advertise:

"i have the network 10.0.0.0" (advertised WITHOUT subnet mask, and implicitly understood by other routers as 10.0.0.0/8)

OR would it auto-summarize in a non classful way like:

"i have 10.1.0.0/22" (advertised as network id and subnet mask pair)

In other words, does turning on auto-summarization in RIPv2 (or other classless routing protocols) cause it to auto-summarize in a classful manner or simply auto-summarize classlessly to the best of its ability?

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