All things related to multicast

[Hitoshi Asaeda <>]

> Right, I've also seen this happen. I must confess that whenever I hear
> of an IGMP related problem I think of the switches as the most likely
> culprit. I know of cases where there have been as many as 5 switches
> between the router and the host. It didn't take too long to find out
> that the regular IGMP queries from the router never reached the host,
> but it's quite tedious to find out which of the 5 switches discard it.

Adding the following spec and implementation on the host-side IGMPv3
could give some sort of the solutions?

"If an IGMPv3 host does not receive any IGMP query message within some
period (*) after it sends IGMPv3 join message, the host recognizes that
some switches toward its upstream router may not forward IGMPv3 report
or query messages. In this case, the host may want to switch its host
compatibility mode to IGMPv2 and send the IGMPv2 report that
corresponds to the previous join."

(*) defining "some period" is important, in order not to fall back the
router's compatibility mode to v2 unnecessarily.
--
Hitoshi Asaeda