[j-nsp] Multicast through a switch

[Alexander Marhold]

Turning off IGMP-snooping means that every MC will be sent out on all
interfaces within the same vlan. ( like broadcast)

Turning OFF is needed when you have a pure Layer2 Multicast environment und
you cannot turn on any multicast Querier. or irb-interface with PIM enabled,
or.... ( every vendor has different solutions for pure L2-multicast to
overcome that problem)

The reason for that is that IGMP is a softstate protocol and the
IGMP-querier will check via asking if there  are still interested listeners
on that LAN, if no answer the multicast stream will be turned off, by the
Querier, or if there is no querier it will be turned off by the switch doing
IGMP-snooping after timeout ( typically 180 sec)

And the behavior is the same for all enterprise switches when they support
IGMP-snooping ( not only EX3300)

With best regards

alexander

-----Ursprüngliche Nachricht-----
Von: juniper-nsp [mailto:juniper-nsp-bounces at puck.nether.net] Im Auftrag von
Gert Doering
Gesendet: Dienstag, 9. Januar 2018 09:19
An: juniper-nsp at puck.nether.net
Betreff: Re: [j-nsp] Multicast through a switch

Hi

On Mon, Jan 08, 2018 at 03:51:22PM -0600, Chris Adams wrote:
> Now we're trying to pass the feed through a VLAN to a new connection 
> through a switch (a VLAN on a trunk from our router to a VLAN on 
> another trunk to the transport carrier), but we're not sure how to get 
> the switch to pass the traffic.  I guess there's something we need to 
> configure static on the switch, but I don't know what.

"just passing through multicast" (as in "same VLAN") should not need any
special configuration.

OTOH, at least EX3300 like to eat multicast unless you turn off IGMP
snooping ("delete protocols igmp-snooping") - which, annoyingly, is
on-by-default.

Without any "smarts" in the switch, multicast is just like broadcast.

gert

--
now what should I write here...

Gert Doering - Munich, Germany
gert at greenie.muc.de