Re: [lwip-users] multicast and join group issue

[Bob Scheffler]

Just remember that IP multicast terminates in an Ethernet broadcast. If your
switch supports IGMP snooping, it will keep the Ethernet broadcast off all
the ports. If the switch never sees the IGMP (or got confused) it probably
will send all Ethernet broadcasts out ALL switch ports. This is a fail-safe
for most smart switches. A cheap switch usually doesn't support IGMP
snooping, so it will broadcast all Ethernet broadcasts out ALL switch ports.

Probably with your testing, the switch got confused. The "good reset" caused
it to begin snooping again, and thus sending the broadcasts only out the
switch ports that sent an IGMP Membership Join. Do you see any IGMP
Membership Queries? Whoever the rendezvous point is should be sending
membership queries. This is to prune any members of the multicast that have
'dropped' off. If this is a small LAN, you probably don't see any of that,
and it is a simple IGMP snooping situation.

Bob
-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of pcu
Sent: Monday, May 12, 2014 1:57 AM
To: address@hidden
Subject: Re: [lwip-users] multicast and join group issue

Now it works, without in the firmware...

May be after a good reset of switch, pc and router.
And the messages are not more broadcasted, just send to the right devices.

Pierre



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