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Re: MSDP & MBGP posted 05/26/2008
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Hi Thor,

You could have two AS# with separate IGP and a requirement to not leak unicast routes in between.
In that situation for RPF purposes you'll have to use MP-eBGP. Please note that you'll need to advertise your AS's RP address but also the prefixes describing your sources (MSDP will send SA message containing both to the remote RP).

On your second question - mesh MSDP groups are not obligatory and you can live without such and I don't expect the lab to ask you anything more then just configuring a mesh group between say two RP.
You can expect a task that asks you to prevent a MSDP "speaker" to forward a received message to other speakers (since MSDP mesh-groups are fully meshed the forwarding is disabled), unless they tell you directly to confgure the mesh groups ;)

As for the RPF source preference, your list is correct.

Regards, Rado

Thor Kopp wrote:
I was working on an lab with MSDP & MBGP only to realise that Multicast BGP
was doing nothing ie if i just has ipv4 unicast BGP working with my MSDP
peers, multicast worked fine. Can anyone give me a few scenarios owhen we
would need to use multicast BGP and also mesh groups under MSDP as i'm a
little hazzy on those as well.

The only thing that i can think of with multicast BGP is if you had an rfp
failure based on your unicast routing table and you weren't allow to use the
'ip mroute' command, then you could advertise your RP within multicast over
a different peer to override your standard rpf check as MBGP routes are
preferred over unicast routes. Is my understanding correct here?

1. Static mroutes
2. DVMRP routes
3. MBGP routes
4. Unicast routes

- Thor

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