From: Peter van Oene (pvo@usermail.com)
Date: Thu Dec 05 2002 - 20:42:19 GMT-3
At 05:40 PM 12/5/2002 -0500, Wargo, Edwin wrote:
>Michael,
>
>Here's a copy/paste from RFC 1965
>(http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc1965.html):
Keep in mind this RFC deals with BGP confederations, which Michael wasn't
running as far as I can tell. RFC 1771, or better yet the recent draft-18
of the BGP spec from the IDR group would be a more accurate source for BGP
info.
>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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