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Re: [Idr] Progressing draft-bhatia-bgp-multiple-next-hops-01.txt



Joel:

They are different routes on the RS as the AS-PATHs are different. Each client needs to prepend its AS number when advertising to the RS. (The RS may skip its own AS number in advertising.)

-- Enke

Joel M. Halpern wrote:

I am missing something. I don't believe that "all" the routes requires the inclusion of redundancy. Whether R1 or R2 sends the advertisement, with the same AS Path and the same Next Hop (R2), there is no need for the route server to send that advertisement twice. it will not add information.
Yours,
Joel


At 03:54 PM 8/25/2006, Enke Chen wrote:

Manav:

Manav Bhatia wrote:


We had some feedback from the IX operators where they wanted asymmetric routes exchange. That is, while the IX clients would advertise their best routes, the route server needs to advertise *all* the routes learnt from all its IX clients to each client. Adding a bit in the capability that does this didn't seem to be much of an overhead! :)


Here you emphasize the need for the route server to advertise *all* the routes. I think that is valid, and a solution must be able to accomplish that. This point is also presented in your proposal:

-----------------------------------------------------------------------------------------------------------


9.3 eBGP mesh scaling at IXes via Route Servers [...]

  If there were a mechanism in BGP to allow an IX route-server to pass
  all other advertisements to a customer peer, without performing any
  path selection or applying any policy, then ...

-----------------------------------------------------------------------------



Let us look at this example:


(X) R1 R2 R3 | | | -------------------------- | RS


The RS peers with R1, R2, and R3 and advertise *all* the routes back.

However, once R1 and R2 start to peer with each other:

   - R1 learns X from R2.
   - Both R1 and R2 advertise X (with R2 as the nexthop) to RS.

How does RS advertise two paths from R1 and R2 for X to R3? (The two paths
have the same nexthop, but different as-path attributes).


-- Enke



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