From: Michael Snyder (msnyder@xxxxxxx)
Date: Thu Aug 15 2002 - 11:52:45 GMT-3
^4 [0-9]* [0-9]*$
Would match any AS that was directly connected to an AS that was
directly connected to AS 4. Is this correct?
Also I think the expression you cited ^_4_[0-9]*$ is different than
^4_[0-9]*$. If they are the same, why not use the shorter one?
Please Advise
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Chaim Gev
Sent: Thursday, August 15, 2002 8:13 AM
To: msnyder@ldd.net; raj.bahad@totalise.co.uk
Cc: ccielab@groupstudy.com
Subject: RE: Filtering BGP updates using ip as-path access-lists
The "*" means "match 0 or more sequences of the pattern" which is null
in
your suggestion.
^_4_[0-9]*$ is more accurate if you are asked to filter exactly AS4 (and
not
AS14).
>From: "Michael Snyder" <msnyder@ldd.net>
>Reply-To: "Michael Snyder" <msnyder@ldd.net>
>To: "'Raj'" <raj.bahad@totalise.co.uk>
>CC: <ccielab@groupstudy.com>
>Subject: RE: Filtering BGP updates using ip as-path access-lists
>Date: Thu, 15 Aug 2002 07:52:31 -0500
>
>I'm no expert on as-path access-lists.
>
>But, I believe the $ is the main difference.
>
>^4_ anything beginning with as path 4.
>
>^4_[0-9]*$ anything beginning with as path 4 and ENDS with one
>additional AS.
>
>Which brings up a question of mine,
>
>Why wouldn't ^4_*$ do the same thing?
>
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Raj
>Sent: Thursday, August 15, 2002 7:02 AM
>To: ccielab@groupstudy.com
>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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