[Xorp-users] IGMP report group ...?

[Bruce M Simpson]

Hervé Léonard wrote:
> The flag 'ALLMULTI' for the network card driver (in ifconfig) was not the
> root cause of the group membership in xorp router.
> It was in fact the IGMP version number for the interface in Xorp
> configuration.
> With the IGMP version 2 (by default) the IGMP membership doesn't work. But
> with version 3, it does.
>   

Pavlin's already covered most of the technical points here, so I'll be 
brief:

Those could in fact be overlapping issues, as IGMPv3 uses a single 
link-scope group address for its reports -- therefore a strictly IGMPv3 
querier does not need to have the ALLMULTI mode set on the interface, 
although as it SHOULD listen for old version hosts, this still breaks 
the spec.

A multicast router does of course need to be listening on all groups 
regardless of whether IGMP is running or not, otherwise it may not be 
able to forward multicast traffic.

You haven't mentioned which network driver you're using in Linux, so 
broken ALLMULTI filtering still can't be ruled out as the root cause.

thanks
BMS