RE: Filtering BGP updates using ip as-path access-lists

From: steven.j.nelson@xxxxxx
Date: Thu Aug 15 2002 - 09:23:15 GMT-3

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Raj

I would use ip as-path access-list 1 permit ^4_[0-9]*$

This Reg Exp says permit 4 and any derivative of the numbers 0 through 9

With this reg exp you can match any as regardless of AS number.

Thanks

Steve

-----Original Message-----
From: Raj [mailto:raj.bahad@totalise.co.uk]
Sent: 15 August 2002 13:02
To: ccielab
Subject: Filtering BGP updates using ip as-path access-lists

Hi all,

I've come across a scenario for which I require some clarification.

I want to permit only networks originated from AS4, and AS's directly
attached to AS4. I use the following config to meet the requirements,
however I have come across documentation that has achieved the same results
using a slightly different version. I've listed both of them below:

ip as-path access-list 1 permit ^4_

and the other being:

ip as-path access-list 1 permit ^4_[0-9]*$

Could someone please help clarify why one method would be preferred over the
other?

Thanks,

Raj.

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