Filter the default route, but accept all other routes

Question

I have a BGP session where the other participant is advertising the default route in addition to a number of small prefixes.

I want to filter out the default, but accept those other prefixes.

I've tried to use:

ip prefix-list no-default-route seq 5 deny 0.0.0.0/0

In combination with:

neighbor 10.4.1.1 prefix-list no-default-route in

But that ends up filtering all of the smaller prefix routes as well.

Is there a way I can filter out the default, but accept all other prefixes?

Remember, prefix-lists (just like access-lists) have an implicit deny statement at the end. You're denying 0.0.0.0/0 as well as everything else. — Ryan Foley, Commented Sep 9, 2014 at 9:14
Thanks for pointing that out -- it didn't dawn on me that there is an implicit deny. — Elliot B., Commented Sep 9, 2014 at 18:34

generalnetworkerror · Accepted Answer · 2014-09-10 06:04:09Z

8

You need to add a statement to explicitly allow those prefixes after denying the default-route, so the final prefix-list becomes:

ip prefix-list no-default-route seq 5 deny 0.0.0.0/0
ip prefix-list no-default-route seq 10 permit 0.0.0.0/0 le 32

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answered Sep 9, 2014 at 6:46

Teun Vink

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Paul Tobias · Accepted Answer · 2017-11-20 11:15:57Z

1

The accepted answer is correct. Another way of writing the same thing, with just one rule, would be:

ip prefix-list no-default-route seq 5 permit 0.0.0.0/0 ge 1

answered Nov 20, 2017 at 11:15

Paul Tobias

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2 Answers 2