mesh network vs broadcast/multicast question

[Alexander Larsson]

Hi dan, I have some questions on the mesh network for the updates work.

What is the broadcast domain for a laptop on the mesh? (I.E. how far are
broadcast messages sent)? Is it just the set of nodes reachable from
your machine, or are broadcasts forwarded by the mesh?

This affects how avahi works, as avahi only uses local broadcasts.

Another question is on multicasts. How many hops do multicast packets
live on the mesh? And are there any other limits than nr of hops to
avoid multicast loops? (Otherwise its likely that nodes see multicast
packages many times, especially in dense networks.)

I read on the olpc wiki about the mesh using three different channels.
My understanding on this is that these pretty much generate three
separate mesh networks that are routed between by the school server, and
that laptops can end up on any channel. 

Does this mean that two laptops next to each other can be on two
completely different networks? This means broadcasts (and by extension
Avahi) cannot reach from one laptop to the other. Is this true? And are
we doing something to work around this (like letting users manually
switch channels)?