All things related to multicast

[Bill Owens <>]

	I have been given a multicast routing problem to solve for 
NYSERNet, and I am hoping to get some hints on it. We currently have 
a native ATM backbone, so those NYSERNet sites that are running 
native multicast just have it flowing across their PVC's to Abilene. 
However, we're contemplating a project that would replace our ATM 
switches with routers, and therefore enable/force us to be involved 
in the multicast routing.

The problem is that we need to do this with fairly minimal 
configuration. I'm casting about for solutions that will allow us to 
implement some subset of functionality soon and give us reasonable 
capability in the short term, then fill in the rest later. I've gone 
over the Connecting Multicast Domains draft, looked at a few other 
configurations, and come up with the following.

Our plan has Juniper M20 routers at both ends of our network, 
connecting to Abilene in NYCM and CLEV. The new backbone routers 
would be connected between those Junipers, and our customers 
connected to them. For unicast routing, the Junipers and the new 
backbone routers will be in one AS, and each of the campuses will 
each have their own, EBGP peering with us. Most of the campuses run 
OSPF internally, some have EIGRP (and one has RIP ;)

For multicast, one of the Junipers would peer with Abilene using MSDP 
and MBGP, and run PIM-SM, and act as an RP for both the backbone 
routers and the customers. I *think* that both the backbone routers 
and the customers' edge routers could run just PIM-SM with the 
Juniper as the RP. So in crude ASCII terms, a customer's connection 
would look like this:


 ---------          -------------          --------          ---------
|         |        |             |        |        |        |         |OSPF or
| Abilene | EBGP   | Juniper M20 | IBGP   |   NN   | EBGP   | NN Cust |EIGRP
|   GSR   |--------|  (Buffalo)  |--------| Router |--------|  Cisco  |--->
|  CLEV   | MBGP   |    *RP*     | PIM-SM |        | PIM-SM |  75xx   |PIM-SM
 ---------  MSDP    -------------          --------          ---------
            PIM-SM

Since the Juniper is the RP for the entire network, it would know 
about all our sources and could advertise them with MSDP. I think 
that would allow us to avoid using a multicast default router 
internally, but I'm not sure. I also think that we would be able to 
peer with external multicast networks through our other Juniper as 
well, so long as it used the Buffalo RP, but I'm not sure of that 
either.

I know that this configuration is not the most efficient, and would 
also require that campuses that desire to have internal multicast 
sources run their own RP just for those groups, and we'd have to 
delegate some portion of the adminstratively scoped space to them. At 
some future point, probably driven by the pace of multicast adoption 
within our community, we'd upgrade to the more conventional 
configuration and run MBGP/MSDP at the customer connections as well.

The big question, though, is whether it would work at all. Has anyone 
tried this sort of thing? Does it seem to make sense?

Thanks for any help you can provide,
Bill.