[j-nsp] Proxmox with Multicast & Juniper EX

[Tore Anderson]

* Tore Anderson

> * Jeff Meyers
> 
> > I am mostly confused why the packets passing the core makes a
> > difference at all. For my understanding, igmp-snooping inspects the
> > communication and passes multicast traffic to exactly those who shall
> > receive it. Why isn't this working? I read that this requires an icmp
> > querier. Would it help to configure that querier on one of the
> > routers (it's two routers because of VRRP)? Can anyone explain why it
> > is working on a local switch but not anymore as soon as a 2nd switch
> > is involved in the path?
> 
> You'll need a querier in your network if you want IGMP snooping to
> work, otherwise the switch will remove the host interfaces from their
> subscribed multicast groups after a while. The querier can be one of
> the switches (you must configure a l3-interface on the VLAN), it
> doesn't have to be the upstream routers.
> 
> Other than that there's too little information in your message for me
> to say exactly what your problem is.

After thinking a bit more about it I think the behaviour you're
observing makes perfect sense. When you connect your hosts to one of the
EX4200s, they'll send an IGMP membership report to join the multicast
group in question. The EX4200's IGMP snooping picks up on this, and
multicast communication the two hosts then works (but probably just for
a limited amount of time, as there's no querier that would normally
cause the hosts to renew their membership in the group, so their
membership will likely just timeout eventually).

However these intial IGMP membership reports are not forwarded to the
EX4550, as it is not a multicast-router interface (from the EX4200s'
points of view, at least). So the EX4550 won't be able to learn of the
existence of the multicast group at all. Also, since the uplink to the
EX4550 isn't a multicast-router interface, nor a regular host interface
that's a member of the multicast group, packets destined for the
multicast group won't be forwarded to the EX4550 either.

You really need a multicast querier in the network for this to work...

Tore