From: Matt Mullen (mullenm@gmail.com)
Date: Thu Feb 15 2007 - 17:12:33 ART
Hey Curt,
It's not obvious when AS 54 is your directly connected neighbor, but these
two expressions are really quite different. Routes originating in AS 54
when it is your directly connected neighbor would have an AS Path consisting
of just 54. So in this case _54$ or ^54$ would work just fine. Consider
though what would happen if you had an AS Path of 100 200 54 and you were
trying to match routes originating in AS 54. Now, only the _54$ would
match. The underscore allows matching zero or more occurences of any
character, and thus would allow matching 100 200 in front of 54 whereas
^54$ would not.
-Matt
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
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Thu Mar 01 2007 - 07:38:46 ART