The switch keeps flooding 224.0.0.0/24 with IGMP on, but a report for a
group in that block still made an entry for it, and the entry limited
the group to the ports that reported it. A host announcing mDNS on
224.0.0.251 thereby cut mDNS off from every other port. Such reports
are now ignored, as RFC 4541 asks.
igmp_setup(), which `igmp off` also calls, enabled the lookup of IPv4
multicast in the L2 table. Groups learned while IGMP was on therefore
kept going only to the ports that had reported them, and with reports
no longer trapped nothing updated those entries until a reboot.
The lookup is now enabled in igmp_enable() and disabled in igmp_setup(),
so with IGMP off all IP multicast is flooded again.
Only frames to 01:00:5e:00:00:16 reached the IGMP handler, so v1/v2
reports, which go to the group address, were never seen. The handler
also took the group from the first v3 group record for every type.
Pass all IPv4 multicast to the handler, which takes the IGMP header
from the IP header length, the group from the IGMP header for v1/v2
reports and v2 leaves and from the first group record for v3, and
returns 0 for anything that is not IGMP so it goes on to the IP stack.
The message and record types have names now.
DrDoof
logicog