From: Scott Morris (swm@emanon.com)
Date: Mon Feb 02 2004 - 14:12:10 GMT-3
That is correct. When you are filtering within your confederation (on the
edge?) then you can look at entries within the AS Path to make specific
decisions regarding entries from one particular peer versus another.
I don't have the original e-mail any longer, so I may be answering this out
of context here! But as I recall, you were looking to match things on an
outbound basis (preventing transit perhaps?). And on your outbound edge
router (still part of AS 200), if you matched on an empty AS Path (^$), then
you would only get things from within AS 200, which would not include your
confederation peers.
You have to remember that this type of filtering takes place before the part
of code where sub-confed AS information is replaced with the confed-id. So
at that point in time, you may have an existing AS Path of 65026 65027.
When AS 300 sees it, it will just have an AS Path of 200. But you need to
match ahead of time, and there IS still an AS Path, and one that is not
empty.
Hope that helps.
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, CISSP,
JNCIS, et al.
IPExpert CCIE Program Manager
IPExpert Sr. Technical Instructor
swm@emanon.com/smorris@ipexpert.net
http://www.ipexpert.net
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
kasturi cisco
Sent: Monday, February 02, 2004 10:27 AM
To: swm@emanon.com; sam6626@yahoo.com; bmcgahan@internetworkexpert.com
Cc: ccielab@groupstudy.com
Subject: RE: AS-Path Filtering with BGP Confiderations!
Guys,
What i am getting confused about is this Q ? Could someone kindly
explain: Now i know within a Confed say AS 200 there are Sub AS like 65026,
65027 etc. These are confed peers. Now when a router in As 300 sees the
routes from this confed wont it see it coming from 200. So when we filter
the routes say locally originated ^$ wont it filter all the sub AS.
Is this required or am i getting it wrong ? Hossam tried to explain but
looks i am dumb. Please explain.
Good Luck,
Kasturi.
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