RE: ip prefix-list [bcc][faked-from]

From: marvin greenlee (marvin@ccbootcamp.com)
Date: Tue Jan 11 2005 - 19:49:12 GMT-3


Did you clear your BGP process after changing your filtering? What is the
rest of your BGP config?

- Marvin Greenlee, CCIE#12237, CCSI# 30483
Network Learning Inc
marvin@ccbootcamp.com
www.ccbootcamp.com (Cisco Training)

-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Tuesday, January 11, 2005 2:38 PM
To: Group Study
Subject: ip prefix-list [bcc][faked-from]
Importance: Low

Hey guys,

Here's something interesting.

It took me a while, but finally I got it into my head how to create an

ip prefix list ie if you have something like this:

ip prefix-list ALLOW-BGP-IN seq 5 permit 112.0.0.0/5

the slash without being followed by a le or ge means

the prefix must = 112.0.0.0 and the mask must be 248.0.0.0

This also means that 112.0.0.0/8 wouldn't match.

Does everyone agree?

Well, I just came across a scenario which breaks this rule.

I was using the above prefix-list to filter all routes except

112.0.0.0/8
113.0.0.0/8
114.0.0.0/8
115.0.0.0/8
116.0.0.0/8
117.0.0.0/8
118.0.0.0/8
119.0.0.0/8

It worked but based on the rule above it shouldn't have, right?

Can anyone explain why my seemingly "incorrect" prefix-list

allowed those routes?

TIA, Tim



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