mesh network vs broadcast/multicast question

C. Scott Ananian cscott at cscott.net
Tue Jun 26 11:06:35 EDT 2007


On 6/26/07, Dan Williams <dcbw at redhat.com> wrote:
> On Tue, 2007-06-26 at 15:22 +0200, Alexander Larsson wrote:
> > 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?

You can specify the hop limit at layer 2.  IPv6 also allows
link-local, site-local, and global multicast addresses, so you can
determine whether how far you want your multicast to go.

> > 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.)

Mesh broadcast, as I understand it, uses a "flood-fill" approach.
Each node maintains a small buffer of broadcast messages that it has
seen recently.  If it receives a packet that it has not yet seen, it
relays it to all of his neighbors.

It's not perfect, but improving mesh broadcast/multicast is an
independent task which doesn't have to be done immediately.
  --scott

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                         ( http://cscott.net/ )


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