From: Huan Pham (pnhuan@yahoo.com)
Date: Fri Jan 09 2009 - 22:47:14 ARST
Bgp does not use the concept of split horizon. Bgp can peer over more than one hop away, so it does not really care how (I.e. via what interface) routes are exchanged.
I cannot read your topology properly so I cannot tell exactly where problem is. Few general suggestions you can check:
- make sure bgp peerings are up
- double check RR config
- check what is next hop advertized via bgp. You have to have reachability to the next hop or bgp route is not installed. Use next hop self on the "edge" router for the iBGP session to change next hop advertised to iBGP peer if required
- check bgp community attributes. No-advertise may stop RR from advertise routes received from one client to others
- post full bgp config , I will have a look at it when I have access to my pc
Sent from my iPhone
On 10/01/2009, at 10:03 AM, Nitro Drops <nitrodrops@hotmail.com> wrote:
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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