All things related to multicast

[Bill Owens <>]

On Fri, Jun 11, 2010 at 09:23:41AM +0300, Zenon Mousmoulas wrote:
> Quite similar to "ip route 0.0.0.0", the default route is installed  
> with "ip default-network" (gateway of last resort) pointing to a  
> network which is known by eBGP (announced from GRNET).
. . .  
> So the difference is you have a static default route pointing to the  
> IP next-hop, while they are pointing it to a network learnt via BGP  
> from GRNET. However "ip default-network" does not have a multicast  
> counterpart; perhaps they could use "ip route" and "ip mroute" instead.
> 
> However, the question is: does MSDP work for you in this case? Would  
> it accept an SA where the originator would match this default route in  
> an RPF lookup?

I can't test that without tearing out the mBGP configuration and replacing it 
with a static route, since the static unicast default points to our 
commercial ISP, and (unsurpisingly) they aren't multicast-capable. This is a 
common configuration within our membership, since NYSERNet only carries R&E 
traffic and our members rely on a commercial network for regular Internet 
access. The router will be configured for full R&E routes (uni and multi) and 
a simple default points to the commercial ISP.

I did take a look at the Cisco docs, and they seem to say that MSDP only 
checks BGP or mBGP routes, there's no mention of static:

 How RPF Check Rules Are Applied to SA Messages
 
 The rules that apply to RPF checks for SA messages are dependent on the BGP 
peerings between the MSDP peers:
 
 •Rule 1: Applied when the sending MSDP peer is also an interior (M)BGP peer.
 
 •Rule 2: Applied when the sending MSDP peer is also an exterior (M)BGP peer.
 
 •Rule 3: Applied when the sending MSDP peer is not an (M)BGP peer.
 
 RPF checks are not performed in the following cases:
 
 •If the sending MSDP peer is the only MSDP peer, which would be the case if 
only a single MSDP peer or a default MSDP peer is configured.
 
 •If the sending MSDP peer is a member of a mesh group.
 
 •If the sending MSDP peer address is the RP address contained in the SA 
message. 
 

I think there might be cases within NYSERNet where there isn't BGP running on 
the MSDP speaker, but we might be getting away with that because of the first 
rule under the second section, "If the sending MSDP peer is the only MSDP 
peer". Your user has MSDP sessions with two routers, and I don't think we 
have that configuration anywhere.

Bill.