BGP Question: Problems with connectivity when using local prefere nces

Devon True dtrue at
Fri May 4 01:28:14 UTC 2001


We are running BGP4 between Sprint and UUNet. We are using route-maps to add
local preferences to certain AS numbers to force traffic out Sprint rather
than UUNet. One of the AS's we force out Sprint is AS3356 (Level3). 

Our CTO has a DSL line from a local provider. When he traceroutes from his
DSL connection, he goes across the DSL provider, Level3, and stops at UUNet.
When I run a traceroute to his DSL IP, I go across UUNet, Level3, and stop
at the DSL provider's router.

Here is the AS path that my traceroute takes: AS701 -> AS3356 -> AS12050
Here is the AS path that his traceroute takes: AS12050 -> AS3356 -> AS701

We are forcing Level3 routes out our Sprint connection, but AS12050 routes
go out UUNet (no local-preference change).

When I took out Level3's AS from our route-map, thus sending Level3 routes
out UUNet, everything worked fine. He could reach us and I could him. Any
ideas why?

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