Subject: Re: [Roll] Question about RPL and multicast

From: "Pascal Thubert (pthubert)" <[email-masked]>
Date: Fri, 4 Feb 2011 17:07:30 +0100

Hi Mounir,

RPL supports a multicast service for storing mode only. So there is no
tunnel. And the multicasted packets are copied at L3, not L2.

A node that wishes to listen to a group will send a DAO to (at least and
usually) one selected parent. Recursively, the DAO reaches the root, and
a RPF path is created for that listener.

As a result a router has DAO entries for all children that are ancestors
listening to a mcast group. It copies the mcast packet to all its
children, as opposed to unicast where it copies to only one child. And
it copies to the selected parent as well. It should refrain from copying
to the node that passed the packet, which should be a waste.

Do you have a specific issue with this?)

Pascal

http://www.xtranormal.com/watch/7011357/

From: [email-masked] [mailto:[email-masked]] On Behalf Of
KELLIL Mounir
Sent: Thursday, January 27, 2011 5:30 PM
To: roll WG
Subject: [Roll] Question about RPL and multicast

Dear all,

In the last version of RPL draft, it is mentioned that an RPL node (a
router) forwards multicast data to the preferred parents and to the
children that have subscribed to the multicast group. Yet, it is not
clear whether this packet forwarding is achieved through IP tunnelling
(multicast-in-unicast) or using L2 (unicast) relaying? (I'd say the
second is right, but I'm not sure). And, the same question arises for
the case of the multicast source within the DODAG..

Best regards

Mounir