[vlc] SOLVED (well, sort of): IGMP snooping on Foundry EdgeIron 4802F

[Bruno Treguier]

Hello everybody,

Several months ago, I posted a message about a strange behaviour of an
EdgeIron switch 4802F, which would cut off the stream when an "IGMP
Membership report" was sent by a client, and would allow the stream on
reception of an "IGMP Leave Group"... :-/

The solution was finally sent to us by Foundry: one must NOT use
multicast addresses lower than 224.0.7.0 on these switches, as IGMP is
not taken into account on those addresses... This is rather weird, as
(if I'm not mistaken) this limitation is not part of any draft or RFC...

And of course it's not written in any of the switch's docs either ! :-)
And yes (Murphy's law), we were using one of those forbidden addresses
(and were miles away of thinking our problem could be related to that !).

When using addresses from 224.0.7.0 up, everything is fine, except that
when you don't have a multicast router and are multicasting on a single
LAN, you must rely on the switch's functionalities in order to generate
IGMP Queries. And on the 4802F, only 10 ports out of 48 (or 24 for the
2402F) can use the internal query generator simultaneously. On the 38
(or 14) other ports, as no query is generated, the clients do not send
periodic membership reports other than the (unsolicited) first one when
they join a group. The timers associated with those unlucky ports
eventually timeout, and the stream is cut off after 4 minutes or so
(default timeout around 260 seconds)...

Hopefully, their new generation switches (4802CF) do not seem to suffer
from any of these "features" and their behaviour regarding IGMP seems
rather sound.

I hope this message will seem to you as factual as I meant it. It's in
no way "Foundry bashing". My purpose is just to inform other people of
the behaviour of the switches we are using here, just in case someone
else stumbles on the same problems (we've lost a LOT of time digging
into this).

Best regards,

Bruno

P.S.: vlc is GREAT ! ;-)

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