From: Nitro Drops (nitrodrops@hotmail.com)
Date: Fri Jan 09 2009 - 21:03:35 ARST
Hi Guys,
Can BGP prefixes be learned from a IBGP peer neighbor and resend out to
another IBGP peer neighbor from the SAME interface, with route-reflector
client configured?
Understand BGP doesnt use 'split-horizon', for IBGP, it uses loop prevention
via route suppression which requires the use of RR, Confederation, Full Mesh.
R3 F0/0 (AS3) > EBGP > (AS1) F0/0 R4 F0/1 > F0/0 R6 F0/1 > Vlan30 SW1 Vlan 30
> F0/0 R5
AS3 advertising BGP prefixes to AS1, and full L3 reachability
R3 - AS3
R4, R6, SW1, R5 - AS1
R4 - RR client of R6
R5 - RR client of SW1
In the above setup, SW1 is learning the the BGP prefixes from IBGP neighbor
R6, which is non-RR-client of SW1, SW1 being a RR should reflect the BGP
prefixes to R5, learning and sending via SVI Vlan 30.
What i noticed, R5 cant learn the BGP prefixes at all, even though R5 has an
underlying L3 routes to R3.
I even made both SW1 a RR-client of R6, and R6 a RR-client of SW1, still R5
cant learn the prefixes.
Next, i created another new SVI Vlan 20 for the subnet between SW1 and R5
R3 F0/0 (AS3) > EBGP > (AS1) F0/0 R4 F0/1 > F0/0 R6 F0/1 > Vlan30 SW1 Vlan 20
> F0/0 R5
Only, then R5 is able to learn the BGP prefixes.
So my question is, can a single SAME interface be used for learning BGP
prefixes from one IBGP neighbor and sending them to another IBGP neighbor?
Some kind of split-horizon concept here even though BGP doesnt use that.
Anyway BGP commands to disable this?
Cheers
Nit
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