All things related to multicast

[Zenon Mousmoulas <>]

We have not tried announcing a default route for ipv4 multicast yet,  
but we did try the MSDP default peer.

It seems you are allowed to configure more than one default peers:

"[...] the first one is the active default peer as long as the router  
has connectivity to this peer and the peer is alive. If the first  
configured peer goes down or the connectivity to this peer goes down,  
the second configured peer becomes the active default, and so on."

So this is a decent solution after all, at least in the particular  
case, where the downstream (stub) network runs both MSDP peerings on a  
single border router.

On 15 Ιουν 2010, at 8:52 ΠΜ, Zenon Mousmoulas wrote:

> I am afraid incongruent routing, which is what this will typically  
> introduce, may further complicate rather than simplify things, which  
> is what we really want. Nonetheless it is an interesting idea worth  
> exploring. Thanks for the hint.
>
> Best,
> Z.
>
> On 14 Ιουν 2010, at 6:14 ΜΜ, Spurling, Shannon wrote:
>
> > Yes, that is the main downfall. Mostly I used this with smaller  
> > installs with a single RP. Once you get to multi-homed setups,  
> > which is a part of your original note I glossed over, BGP really is  
> > required.
> >
> > One of the nice things about mBGP is that you can send a default  
> > route for only the multicast address family, and not have it  
> > influence their regular unicast traffic. Can you originate a  
> > default just for the multicast address family? Only problem is  
> > trying to weight it so that the proper path is the default and the  
> > failover is available in case of failure on the main path. That  
> > part can get tricky.
> >
> > Shannon Spurling
> > WAN Engineer
> >
> >
> > -----Original Message-----
> > From: Zenon Mousmoulas 
> > [mailto:]
> > Sent: Monday, June 14, 2010 12:36 AM
> > To: Spurling, Shannon
> > Cc: wg-multicast
> > Subject: Re: inter-domain MSDP peering without BGP FIRT
> >
> > MSDP default peer would short-circuit any problem, but it would also
> > render the second MSDP peering useless. We have setup dual BGP and
> > MSDP peerings with different GRNET routers in order to provide
> > redundancy.
> >
> > Thanks for the feedback!
> >
> > Z.
> >
> > On 11 Ιουν 2010, at 5:17 ΜΜ, Spurling, Shannon wrote:
> >
> > > I am going to tell you of a solution I have used with Cisco routers
> > > with reasonable success. You have to be careful about this. I use it
> > > mainly with peers with their own PIM domains and no BGP, or the MSDP
> > > peer/PIM-RP being deep inside their network.
> > >
> > > Use MSDP default-peer and filter the heck out of the SA's, so that
> > > only SA's with their prefixes come from the site, and SA's without
> > > their prefixes go to the site.
> > >
> > >
> > > Shannon Spurling
> > > WAN Engineer
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: Zenon Mousmoulas 
> > > [mailto:]
> > > Sent: Thursday, June 10, 2010 12:57 PM
> > > To: wg-multicast
> > > Subject: inter-domain MSDP peering without BGP FIRT
> > >
> > > Dear all,
> > >
> > > We (GRNET) have a downstream network (let's call them U) who  
> > > receive a
> > > partial routing table from us. U runs BGP and MSDP peerings on a
> > > single border router (RP in their PIM domain) with two distinct  
> > > GRNET
> > > routers (anycast RPs in the GRNET domain, running full-mesh IBGP and
> > > MSDP). The BGP peerings are setup in a primary/backup scheme (using
> > > communities, local pref etc). BGP peerings carry both unicast and
> > > multicast NLRIs, but we use separate sessions for IPv4 and IPv6.
> > > Pretty standard stuff.
> > >
> > > Since U receive only a partial routing table, they rely on the
> > > "default network" mechanism for internet routing. This gateway of  
> > > last
> > > resort is configured once and, AFAIK, can't be set separately per
> > > NLRI. Since IOS (12.2SXF in their case) performs RPF lookups across
> > > both the MRIB and the unicast RIB, it seems to work out fine:  
> > > "show ip
> > > rpf" points to the default network when no prefix matches the  
> > > source,
> > > with a "unicast" RPF type. However MSDP peer-RPF check fails: SA
> > > announcements are rejected when no prefix matches the RP/Originator,
> > > so the default network doesn't apply in this case, or so it seems.
> > >
> > > MSDP debug also logs messages like this:
> > >
> > > Jun  7 18:15:33: MSDP(0): <grnet-msdp-peer>: Peer RPF check failed  
> > > for
> > > w.x.y.z, used IBGP route's peer 0.0.0.0
> > >
> > > which don't make much sense.
> > >
> > > Judging from the above, it looks like we effectively can not MSDP  
> > > peer
> > > with a downstream network without announcing to them (the equivalent
> > > of) FIRT in MBGP. Of course this is not a big issue while the number
> > > of prefixes is low, however there are still practical reasons  
> > > against
> > > this, namely avoiding incongruent routing.
> > >
> > > Have you ever noticed this? I have a feeling that enforcing  
> > > compliance
> > > to RFC3618 (ip msdp rpf rfc3618) would affect this behavior, but I'm
> > > not even sure if their border router supports it.
> > >
> > > Thanks in advance,
> > > Z.