Auto-Summarization

wshenry

I need some help with understanding auto-summarizing routes on the various routing protocols. I'm aware the VLSM makes it easier for routes to be summarized and save bandwidth on the network.
I want to know about classful and classless ip address in its relation to summarization (supernetting)
just a bit confused with this topic, can someone please help?

2lazybutsmart

You've asked 10 questions in a couple of sentences. are you a lawyer?

You know what summarization is right? You have like 10 subnetted networks of a classful address and you summarize them by sending the classfull address instead of all 10 networks. You can also do more detailed summarization, but that's the main idea.

All classful protocols don't send subnet information with their route updates, so classful protocols don't support VLSM nor summarization.

Classless protocols send subnet information via route updates and therefore support summarization, VLSM, CIDR, the works.

EIGRP and OSPF are two classless protocols. RIP and IGRP are classful. You can have variabally subnetted masks with the former two but not the latter. You can also manually summarize with EIGRP and OSPF. EIGRP auto summarizes by default.

There's something called discontiguous networks, and that's when two networks of a classful address are connected together by another network of a different classfull address. In this scenario, EIGRP will auto summarize at boundaries which means the discontiguous network scenario won't work unless you turn off auto summarization.

OSPF, on the other hand, doesn't auto summarize so it supports discontiguous networks by default.

2lbs.