From: Wargo, Edwin (EWargo@greenwichtech.com)
Date: Thu Dec 05 2002 - 19:40:25 GMT-3
Michael,
Here's a copy/paste from RFC 1965
(http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc1965.html):
AS_PATH modification rules
Section 5.1.2 of [1] is replaced with the following text.
When a BGP speaker propagates a route which it has learned from another BGP
speaker's UPDATE message, it shall modify the route's AS_PATH attribute
based on the location of the BGP speaker to which the route will be sent:
a) When a given BGP speaker advertises the route to another BGP speaker
located in its own autonomous system, the advertising speaker shall not
modify the AS_PATH attribute associated with the route.
b) When a given BGP speaker advertises the route to a BGP speaker located in
a neighboring autonomous system that is a member of the local autonomous
system confederation, then the advertising speaker shall update the AS_PATH
attribute as follows: <end of paste>
R5 won't modify the AS_Path attribute for iBGP peer R2. R2, however, will
modify it's AS_Path attribute for eBGP peer R1.
HTH,
Edwin
-----Original Message-----
From: Michael Todd
To: ccielab@groupstudy.com
Sent: 12/5/02 4:46 PM
Subject: Weird AS prepend problem
I'm trying to prepend AS numbers to outgoing updates on a router that is
originating the routes. When I look at the neighboring router, the AS
numbers weren't added. If, from a router not originating the routes, I
add the same route-map to an outgoing neighbor, the AS numbers are
prepended. I'm using the exact same route-map and access-lists on both
routers. Should I be able to prepend an AS path to an IGP neighbor if I
am originating the routes? Any ideas?
Visual:
R5 AS 200------------------R2 AS 200--------------R1 AS 8888
R5 originates 172.32.1.0 from a loopback using a network statement.
Outgoing route-map to R2 matches 172.32.1.0 and sets as-path prepend to
500 and 501. Clear IP BGP *, then look in R2, no dice. See the route,
but not from 500, 501. If I put the same route-map on the R2 for R1
neighbor, R1 sees 500 501.
I'm tearing my hair out! I've triple-checked the configs. I'm running
12.1(5)T9 on all routers. Nothing else special happening with BGP.
Thanks in advance!
Michael Todd
.
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