From: Jason Morris (mcnever@gmail.com)
Date: Mon Jan 12 2009 - 20:24:39 ARST
> 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
>
one thing note worthy if i'm remembering correctly, the next hop
address has to be reachable by a route more specific than a 0.0.0.0/0
route correct? so if your using a default route on R5 pointing to the
address on F0/0 of R3 (which is what your next hop should be if your
not changing it), the route wont be injected.
semi related question...
next hop unreachable will keep it from showing up in the BGP as well
as the routing table correct?
what if you do a show 'ip bgp nei x.x.x.x received-routes'... will it
show up in that list?
Thanks
Jason
On Fri, Jan 9, 2009 at 7:47 PM, Huan Pham <pnhuan@yahoo.com> wrote:
> 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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