bgp convergence problem

[Song Li <refresh.lsong () gmail com>]

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