All things related to multicast

[Hitoshi Asaeda <>]

> and my understanding is that some routers can be configured
> to ignore igmpv2 (or v1) messages for groups in 232.x.x.x so
> an igmpv2-only host cannot break ssm by forcing an ssm group
> into v2 compatability mode.

Just a reminder.

My IGMPv3/MLDv2 host-side implementations (incl. KAME) can avoid to
switch a host compatibility mode back to an older version.
You can configure your host to surpress it by sysctl(8), like;
        # sysctl -w net.inet.igmp.always_v3=1
        or
        # sysctl -w net.inet6.icmp6.mldalways_v2=1
and then your host always sends igmpv3/mldv2 report messages.
(Both default values are "0", meaning "act in compatibility mode".)

However, remember that you must know your host *always* sends
igmpv3/mldv2 report messages on *all* interfaces after making this
configuration, whereas this is (probably) the simplest way to escape
from some DoS attacks or accidents.
Thus, you may want to use it only when you are confident that your
host does not need to behave as an igmpv2 node, for example.
--
Hitoshi Asaeda