[c-nsp] Problem switching from IGMP v2 to v3

[John Neiberger]

We have a few devices that are currently using IGMP v2 and we have
IGMP v2 configured on the switchports for those devices. For various
reasons, we need to change that to IGMP v3. The first step was to
change the configuration on the interfaces to IGMP v3. When we did
that, it broke the multicast stuff and it would not recover. We had to
switch back to IGMP v2 to recover. That doesn't make any sense to me,
though. I thought that IGMP v3 was fully backward compatible to IGMP
v2.

I'm not aware of any differences that would cause this behavior. Are
there some differences between the two that might cause this?

Thanks!
John