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

Michael Richardson <mcr+ietf@sandelman.ca> Fri, 21 December 2012 19:55 UTC

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Subject: Re: [Roll] [roll] #105: trickle-mcast: how to determine scope of MPL domain
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>>>>> "Robert" == Robert Cragie <robert.cragie@gridmerge.com>; writes:
    Robert> <RCC> Almost there. In the case of forwarding using MPL
    Robert> domain (subnet-local) mc address, the inner packet is
    Robert> strictly tunnelled, i.e. there will be no hop count
    Robert> decrementing per hop. I discussed this offline with Jonathan

okay, and this is because the packet is in a tunnel, which is not
addressed to the "link", so in effect, it is not a local packet.

I can buy this, and so #3 does not decrement, while #4 does.

What is the use case for #3 and what is the use case for #4?
What I'm trying to get at here is: what is the argument to have both?

Who is going to need each one?

On 14/11/2012 9:13 PM, Michael Richardson wrote:
> Robert, has written 3 rules about when to encapsulate, and how to
> recognize the MPL domain.  With two options #3 and #4.
>
> the difference is  (#3):
>
>>     2. Outer header will have subnet-local mc address (e.g.
>>        FF03-based). This can be used to control propagation in
>>        conjunction with the MPL option.
> vs (#4)
>
> <    2. Outer header will have link-local mc address (e.g. FF02-based).
> <       This cannot be used to control propagation as it only goes one
> <       hop; the MPL option is used alone
>
> and as far as I can understand in both cases MPL forwarders will
> decapsulate and re-encapsulate, thus decrementing the inner TTL each
> time.   Or did I misunderstand here?





-- 
Michael Richardson <mcr+IETF@sandelman.ca>;, Sandelman Software Works 
IETF ROLL WG co-chair.    http://datatracker.ietf.org/wg/roll/charter/