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Thread Index [isp-bgp] Re: Zebra as Route Reflector
On Tue, 2003-07-29 at 01:54, Tulip Rasputin wrote:
>
> I am not sure if the RRs are always supposed to be in the traffic path.
>
> ---[A]\-----------
> \ |
> [RR]---- [C]
> / |
> / |
> ---[B]-----------
>
> A, B and C are 3 clients of the RR. RR here reflects the routes from A and B to C - but doesnt
> come anywhere in the data forwarding path. C can throug some IGP cloud can send data directly to A
> and B.
>
> Isnt this possible?
Possible it is.
It is also possible to mess it up :-) And i just wanted to point that
out. For instance if the IGP distances above all are the same, the RR
will perform path selection based on say router-id... However if B is
closer to C than to A (that is how i interpret your diagram) this may
not be the desired result.
I guess the answer to your question depends on topology, metrics, etc.
> This is then a limitation of the RR. Shouldn't we be addressing it? Lately there have been some
> proposals in the IETF to advertise multiple BGP routes. Will that not help here?
The original purpose of RRs is to aggregate routing information. If you
do not aggregate information (via selecting a subset of available
paths), then you defeat the purpose.
In reality, it seems to me that often people use reflection more as a
configuration aid. But that is probably the wrong tool for the job.
It was originally thought that the number of TCP sessions in a mesh
could be a problem. My opinion is that this is not really an issue. iBGP
meshes w/ several hundreds of routes work just fine.
One could think of a route reflector-like box that doesn't always
advertise just one path and doesn't always advertise all.
But that is a very significant change from the current model.
regards,
Pedro.
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