From: Curt Gregg \(cugregg\) (cugregg@cisco.com)
Date: Thu Feb 15 2007 - 16:38:55 ART
Hey Sidalo,
I agree with your points. I'm trying to understand why _54$ would be
used opposed to ^54$ given the following;
R6 has two paths to AS 54 and their directly connected customers 500 and
600 thru RA and RB.
I need to prefer RA for routes inside of AS 54 and RB for routes to AS
500 and 600.
I used an as-path to match ^54$ and set a high LOC-PREF with a route map
to my neighbor RA and anything not matched by as-path would get a lower
LOC-PREF.
So basically routes to AS 54 would traverse RA and routes to AS 500 and
600 (attached to AS 54) would prefer RB.
I noticed mention of _54$ used instead of ^54$, they both have the same
results however I think to be specific ^54$ should be used to match
anything originating inside of AS 54.
sho ip bgp reg _54$ and sho ip bgp ^54$ show the same results.
________________________________
From: Sidalo [mailto:sidalo@gmail.com]
Sent: Thursday, February 15, 2007 2:16 PM
To: Curt Gregg (cugregg)
Cc: Cisco certification
Subject: Re: Question: BGP REG ^54$ or _54$
^54$ = coming only from AS 54 and passing though no other AS whether
before or after AS 54
_54$ = anything that started in AS 54 and could have passed through
additional AS before reaching you.
^54_ = anything that is coming directly from AS 54 and could have
originated somewhere before reaching AS 54.
On 2/15/07, Curt Gregg (cugregg) <cugregg@cisco.com > wrote:
Question:
Wouldn't these two expressions be the same or you trying to
match
anything originating in AS 54?
ip as-path access-list 1 permit ^54$
^ = start of a line
or
ip as-path access-list 1 permit _54$
_ = beginning of the line (or end of the line or a space)
Wouldn't _54$ also be considered the end of the path or
originating AS
as the as-path describes the AS systems it has passed thru
beginning
with the most recent and ending with the originating AS.
In this case AS 54 is the directly connected AS.
Are there pros or cons to using either or?
TIA
Curt
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