[171547] in North American Network Operators' Group
bgp convergence problem
daemon@ATHENA.MIT.EDU (Song Li)
Tue May 6 00:00:46 2014
X-Original-To: nanog@nanog.org
Date: Tue, 06 May 2014 11:58:58 +0800
From: Song Li <refresh.lsong@gmail.com>
To: NANOG <nanog@nanog.org>
Reply-To: refresh.lsong@gmail.com
Errors-To: nanog-bounces@nanog.org
Hi everyone,
I have one bgp convergence problem which confused me. The problem is as
follows:
+--------+
| AS5 |
+------+16.1/16 |
| +-----+--+
| |
+---+--+ |
| AS4 | |
| | |
++-----+ |
| |
| |
| |
+-----+--+ +-+-----+
| AS2 | | AS3 | 16.1/16 (5)
| ISP | | ISP |
+---^----+ +---^---+
| |
| +--------+ |
+-----+ AS1 +----+
|customer|
+--------+
16.1/16 (2 4 5)
AS1 multihomed to AS2 and AS3, for some reasons AS1 disconnect from AS3,
and as a resutl the route to 16.1/16 will be 16.1/16 (2 4 5).
After a while, the BGP seesion between AS1 and AS3 reestablished but
AS1 leaks the route 16.1/16 (2 4 5) to AS3. At this point,
1/ AS1 will have two bgp routes for prefix 16.1/16: 16.1/16(2 4 5)and
16.1/16(3 5), according to shorter AS_PATH it will select 16.1/16(3 5)
as best route.
2/ AS3 also have two bgp routes: 16.1/16(2 4 5) and 16.1/16(5),
according to local_pref it will select 16.1/16(2 4 5).
in this case, AS1 and AS3 select each other as the best route to AS5, i
wonder which route will be the final best route after bgp convergence in
AS1 and AS3.
Thanks!
--
Song Li
Room 4-204, FIT Building,
Network Security,
Department of Electronic Engineering,
Tsinghua University, Beijing 100084, China
Tel:( +86) 010-62446440
E-mail: refresh.lsong@gmail.com
