From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Tue Aug 22 2006 - 11:36:02 ART
Mengdi,
The originating AS is the one that is at the end of the AS-Path
on the right. If there are other ASes in the transit path between you
and AS 54 then you would need to match _54$ instead of ^54$. If you are
directly connected to 54 then ^54$ would work, but it would exclude and
prefixes that AS 54 is prepending to you.
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Mengdi Cao
> Sent: Tuesday, August 22, 2006 6:24 AM
> To: ccielab@groupstudy.com
> Subject: IEWB Lab 7 Q 5.3
>
> Hi, Buddys,
>
> I am quite confused when doing IEWB Lab 7 Q 5.3 Bestpath Selection.
>
> It reads
> " ... configure your network so that all traffic from AS100 destined
for
> prefixes ORIGINATED in AS 54 transits the link to BB1."
> " ... configure your network so that all traffic from AS100 destined
for
> prefixes that are FROM CUSTOMERS of AS 54 is sent out towards BB3"
>
> From my understanding, "prefixes originated in AS54" should be
directly
> from
> AS 54 (by network statment or redistribution), thus the AS_PATH should
be
> a
> single "54" when entering AS100. Those willl some other things ahead
of
> 54
> should be orginiated from other AS, i.e., "prefixes from customers of
AS
> 54". Thus I designed the answer as:
> !
> router bgp 100
> bgp default local 100
> nei 54.1.7.254 route-m BB1 in
> nei 204.12.1.254 route-m BB3 in
> !
> ip as-pa access-l 1 per ^54$
> !
> route-m BB1 per 1
> m as- 1
> s local- 200
> !
> route-m BB1 per 10
> !
> route-m BB3 per 10
> m as-path 1
> s local- 50
> !
> route-map BB3 per 20
> !
>
> But when I checked it up with the answer I found the answer is roughly
the
> same but it's AS_PATH access list uses _54$ instead of ^54$. From my
> understanding that _54$ matches anything ends with 54. And in this
answer
> it is the same as match anything as this is applying on the EBGP
neighbour
> of AS 54. Thus I can not agree with this answer. Anyone got comments
on
> it?
>
>
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