From: Ravi Singh (way2ccie@googlemail.com)
Date: Tue Feb 17 2009 - 22:33:14 ARST
Hi Group,
I think I might have to go back to basics here. Suppose R1 in AS-1 is
learning a prefix (2.0.0.0/8) from R2 in AS-2 and R-3 also in AS-2 is
connected to R1 & R2 both as in the diagram below
R1 <----->R2
\ |
\ |
\ |
\ |
R3
R1 forms an eBGP peer with R2 & R3 and R2 & R3 form iBGP amongst
themselves. R1 now receives the same prefix(2.0.0.0/8) from R3 as well and
since everything else is same the comparison is made based on router-id & R2
having a lower id (2.2.2.2) wins. Now, if on R1, I shut the BGP relationship
towards R2 the only path will be from R3 as the best path. I turn the BGP
neighbor on again and R1 still shows the path from R3 as the best path even
though R2 peering is up and R2 has a lower router-id.
It stays this way untill I hard reset the BGP peering on R1(or R3). Even a
soft reset serves no good. My question is , is this the expected behaviour
and if yes why so ? I mean shouldn't the protocol be intelligent enough to
recalculate its decisions on receiving prefixes with more preferred
attributes.
Thanks,
Ravi
Blogs and organic groups at http://www.ccie.net
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