Re: IGMP/MLD-Proxying: broken upstream forwarding rule? (RFC 4605 section 4.2)

Mark Doll wrote:
> Hi!
> 
> The IGMP/MLD-Proxying RFC 4605 states in section 4.2. "Forwarding
> Packets":
> 
> [...] A proxy device forwards packets received on any downstream
> interface to the upstream interface, and to each downstream interface
> other than the incoming interface based upon the downstream
> interfaces' subscriptions and whether or not this proxy device is the
> IGMP/MLD Querier on each interface. [...]
> 
> This seems to suggest an unconditional forwarding in the upstream
> direction, which will lead to forwarding loops in any non loop-free
> physical topology (any topology other than a tree). The correct
> forwarding rule must only forward packets received on interfaces, on
> which the proxy is the querier. So the above should read:

RFC 4605 only supports loop-free topologies.  The following text is in 
the Introduction:

    This document applies spanning tree multicast routing [MCAST] to an
    Internet Group Management Protocol (IGMP) or Multicast Listener
    Discovery (MLD)-only environment.  The topology is limited to a tree,
    since we specify no protocol to build a spanning tree over a more
    complex topology.  The root of the tree is assumed to be connected to
    a wider multicast infrastructure.

Regards,
Brian