Re: IGMP report messages..

> I have doubt about IGMP report messages.
> IGMP report messages are sent to group-address.
> Is there any reason why we don't send messages to
> ALL_IGMP_HOSTS ? (at least once in 100 sec.). So

Because a host that does not join a multicast session does not want to
listen the non-membership report. It is fine only the group member
hosts (and routers) listen the corresponding report.
(In fact, if a host speaks IGMPv3, it does not need to listen the
report at all, because of elimination of a report surpression
mechanism. This is not your question I guess, but would be nice to
know.)

> that routers can learn groups dynamically.

A multicast router captures all IGMP reports, even though it is not
the corresponding group member.

> As of now most router implementations does not accept
> packet from any UNKNOWN group. So it can accept packet
> only if router has configuration about possible groups
> in its network.

What UNKNOWN means? Multicast routers listen all IGMP reports.

> Many implementation does not support Router Alert Option as
> well. So what is the soultion for this ?

I think many routers support it.
If I talk about a BSD's host-side implementation, RA option for IPv6
was implemented years ago and the one for IPv4 is included in the
IGMPv3 implementation of KAME.
--
Hitoshi Asaeda