[OpenWrt-Devel] Regarding bridge multicast-to-unicast patch

[Linus Lüssing]

On Wed, Jun 03, 2015 at 07:47:49AM +0200, Steven Barth wrote:
> Do you by chance remember what was the behavior of the Linux kernel's
> intenral querier was.
> 
> I mean does it use the usual L3-address of the bridge as source?

For IPv4 it uses 0.0.0.0 by default and there's an option to use
the IPv4 address of the interface (multicast_query_use_ifaddr).
For IPv6 it always uses the link-local IPv6 address of the bridge.

> How does it behave in the presence of other queriers either on WiFi stas or
> other bridge ports?

For IPv4 if 0.0.0.0 is used and if it hears any other query it'll
become quiet (and will start querying again if that querier
vanished after a certain timeout).

For IPv6 and a non-zero IPv4 source address it'll use the normal
IGMP/MLD querier election mechanism, meaning the one with the
lowest IP address will become the selected querier and the only
one querying on the link.

If the selected querier is behind one of the bridge ports then
any multicast traffic is always forwarded to that port regardless
of the IGMP/MLD reports it got from there.

Cheers, Linus
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