BGP weight

I have a question about BGP weight and how it affects routing on other
routers. Here is an example:

AS100 AS200
R1-------------R2
| |
| |
| |
R4-------------R3
AS400 AS300

Router R4 advertises network 4.0.0.0
Rip runs on all routers and advertises links between routers.

R2 sees two paths to 4.0.0.0 :

  Network Next Hop Metric LocPrf Weight Path
* 4.0.0.0 10.1.12.1 0 100 400 i
*> 10.1.23.3 0 300 400 i

Now, on router R1 I define weight of 50000 for all routes coming from AS200:
# neighbor 10.1.12.2 weight 50000

R2 sees now only one route to 4.0.0.0:
   Network Next Hop Metric LocPrf Weight Path
*> 4.0.0.0 10.1.23.3 0 300 400 i

R2 removed path via R1 which is good thing because this would create a loop.
My question is:
How R2 knows not to use R1 anymore ?

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Received on Fri Nov 19 2010 - 14:30:41 ART