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BGP Path Question posted 08/25/2007
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          R2 (AS2000)
   ----------fa0/0----------
   |                       |
   |e0                     |fa0/0
R8 (AS8000)             R1(AS1000)
   |e1                     |fa0/1
   |                       |
   ----------fa0/0----------
        R3 (AS3000)

eBGP Peerings:
R8--R2
R8--R3
R1--R2
R1--R3

Situation:
R8 is advertising 80.0.0.0/8 with all default attributes.

Result:

R2-2610XM#show ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
*  80.0.0.0         10.10.10.1                             0 1000 3000 8000
i
*>                  10.10.10.8               0             0 8000 i



R1-2611XM#show ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
*  80.0.0.0         10.10.10.8                             0 2000 8000 i
*>                  20.20.20.8                             0 3000 8000 i
R1-2611XM#


R3-2610XM#show ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
*> 80.0.0.0         20.20.20.8               0             0 8000 i



Question:  

Why is R3 not seeing both paths?   Is R1 not advertising the longer 
path to R3 because it is aware that R3 already has a shorter path?

Even if that was the case I would have assumed both paths would be 
seen by R3 but the shortest path via 8000 would be selected as best.


When I debug "ip bgp updates"  R1 does not send an update to R3 for 
that path unless, R3 sends a withdrawal of its existing path.