Re: bgp best path confusion

Thanks Gilles,

I added a R4 to the topology, that connects to R2, R3 and R1 over the
Frame-relay.
now, R4 is a RR too, and is ibgp peer to R3.

now no direct ibgp peering between, R3 and R2.,
and R3 and R2 are route-reflector-client of R1 and R4.

R1------R4
| \ / |
| \ / |
| \/ |
| / \ |
| / \ |
R2 R3

R3#sh ip bgp 2.0.0.0
BGP routing table entry for 2.0.0.0/8, version 17
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Flag: 0x900
  Not advertised to any peer
  Local
    10.1.22.2 (metric 1) from 10.1.13.1 (5.4.2.1)
      Origin IGP, metric 0, localpref 100, valid, internal, best
      Originator: 2.2.2.2, Cluster list: *5.4.2.1*
  Local
    10.1.24.2 (metric 2) from 10.1.34.4 (4.4.4.4)
      Origin IGP, metric 0, localpref 100, valid, internal
      Originator: 2.2.2.2, Cluster list:* 4.4.4.4*

I guess this one goes to rule 13.

On Thu, Aug 30, 2012 at 12:55 AM, Gilles Fabre <fabre.gilles_at_voila.fr>wrote:

> Hi
>
> this looks like a great design...isn't Route-Reflector supposed to remove
> the need for Full-Mesh ??
>
> anyway, I think in this case Rule #12 applies :
>
> 12. If the originator or router ID is the same for multiple paths, prefer
> the path with the minimum cluster list length.
> This is only present in BGP RR environments. It allows clients to peer
> with RRs or clients in other clusters. In this scenario, the client must be
> aware of the RR-specific BGP attribute.
>
> best regards,
> Gilles.
>
>
> > Message du 29/08/12 ` 19h01
> > De : "oo IPX"
> > A : "Cisco certification"
> > Copie ` :
> > Objet : bgp best path confusion
> >
> > i have a hub and spoke topology, R1 being hub.
> >
> > R1-is a Route reflector.
> >
> > also, R1, R2 and R3 are fully meshed ibgp peers. with R1, R2 and R3
> > advertising networks 1.0.0.0/8, 2.0.0.0/8 and 3.0.0.0/8
> >
> > *on what level of the bgp path decision making the following route is
> been
> > chosen?*
> >
> >
> >
> > *R3(config-router)#do sh ip bgp 2.0.0.0
> > BGP routing table entry for 2.0.0.0/8, version 4
> > Paths: (2 available, best #2, table Default-IP-Routing-Table)
> > Flag: 0x820
> > Not advertised to any peer
> > Local
> > 10.1.12.2 (metric 1) from 10.1.13.1 (1.1.1.1)
> > Origin IGP, metric 0, localpref 100, valid, internal
> > Originator: 2.2.2.2, Cluster list: 1.1.1.1
> > Local
> > 10.1.12.2 (metric 1) from 10.1.12.2 (2.2.2.2)
> > Origin IGP, metric 0, localpref 100, valid, internal, best
> > *
> >
> >
> > Network Next Hop Metric LocPrf Weight Path
> > *>i1.0.0.0 10.1.13.1 0 100 0 i
> > ** i2.0.0.0 10.1.12.2 0 100 0 i
> > *>i 10.1.12.2 0 100 0 i*
> > *> 3.0.0.0 0.0.0.0 0 32768 i
> >
> >
> >
> > Regards
> >
> >
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Received on Thu Aug 30 2012 - 01:13:22 ART