Re: [Roll] [roll] #105: trickle-mcast: how to determine scope of MPL domain

["Jonathan Hui (johui)" <[e-mail]>]

On Nov 1, 2012, at 6:47 PM, Dario Tedeschi <[e-mail]> wrote:

> I don't understand what benefit is gained by allowing the use of non-link-local in the outer header, if encapsulation is required. Supporting both link-local and higher in the outer header just servers to complicate the forwarder.

The purpose is to limit the extent to which MPL disseminates a packet to something smaller than the entire LLN (item 2).

> Is item 2 a requirement that a subset of devices in the LLN participate in MPL forwarding and others don't, or is it that there are two MPL domains, or is it that one subset of devices are listening on multicast address A while others are listening on multicast address B? In any case, I don't see how the use of link-local scope in the *outer* header would not work.

As mentioned above, the purpose is to limit the physical extent of MPL forwarders that disseminate a message.  If we use a link-local destination address in the outer header, how do you propose to limit the region?

> As for encapsulation, using an MPL multicast address of the from FF02::00XX, in the outer header, would only add three bytes to the packet after 6lowpan compression.

I agree.

Maybe you could describe a concrete example of how using link-local addresses in the outer header would address Peter's scenario that he posted to the list?

--
Jonathan Hui