kern/138666: [multicast] [panic] not working multicast through igmpproxy

[Andriy Syrovenko]

2009/12/8 Bruce Simpson <bms at incunabulum.net>:
> Andriy Syrovenko wrote:
>>
>> I have switched to 8-STABLE. Kernel does not seem to crash anymore,
>> however IGMP still does not work. tcpdump complains that outgoing IGMP
>> report and leave packets have incorrect checksum- it is always 0.
>> Though I'm not sure weather it is IGMP checksum or IP checksum that is
>> incorrect.
>>
>
> This just sounds like a fairly normal artefact of tcpdump/bpf with checksum
> offload, as I get the exactly same thing on my desktop w/ re(4).
>
> You need to confirm the checksums at the wire to be sure, or disable
> rxcsum/txcsum:
>   # ifconfig re0 -txcsum -rxcsum
I've checked w/ tcpdump on my MacBook connected to the same LAN
segment the upstream interface of my router is connected to. The
packets on the wire have bad checksums. And yes, I have re(4)
interfaces as well. I'll try turning off checksum offloading today
evening, as soon as I get to my router.

> Nothing has changed in the behaviour of the code which computes IGMP
> checksums; it does not depend on the outer IP header, and isn't touched by
> IP checksum offload, unless your network card (or its driver) is doing
> something it shouldn't be doing.
I have looked through the tcpdump source code, and am now fairly
confident that it is IP (not IGMP) checksum that is broken.

> Perhaps Florian can shed some light on your IGMP issue? igmpproxy only
> understands IGMPv2, afaik.
Yep, it is igmp v2 only indeed.