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

[Robert Cragie <[e-mail]>]

On 12/11/2012 10:14 PM, Michael Richardson wrote:
> see inline
>
>>>>>> "Dario" == Dario Tedeschi<[e-mail]>  writes:
>      Dario> Non-link-local would be fine with the following caveats:
>
>      Dario> 1. A non-link-local mc address that *uniquely* identifies the MPL
>      Dario> domain must exist, whether it be IANA assigned or determined at
>      Dario> run-time.
>
>      Dario> 2. A packet injected into an MPL domain that has a mc address that does
>      Dario> not match the MPL domain address must be tunneled.
>
> okay...
> a packet with a link-local mc address does not need tunnelling, because,
> by definition, it can not leave the MPL domain, so it never needs
> tunnelling?

It's not quite as simple as that:

 1. A packet with a link-local mc address doesn't need tunnelling and
    doesn't need trickle multicast as it is intended to go only one hop
    and is therefore sent using link-layer broadcast without any MPL option.
 2. We have generally used the term "subnet-local" in the case of where
    the MPL domain covers the multi-link subnet exactly. If the
    originator is in the MPL domain, and all the intended recipients are
    in the MPL domain, then any packet forwarded by a MPL forwarder will be:
     1. Unencapsulated
     2. Have subnet-local mc address (e.g. FF03-based)
     3. Have a MPL option
 3. There is the other case where if the originator is not in the MPL
    domain or at least one of the intended recipients is not in the MPL
    domain (scope rules), then any packet forwarded by a MPL forwarder
    will be:
     1. Encapsulated
     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.
     3. Outer header will have a MPL option
     4. Inner header will have site local mc address (e.g. FF05-based).
        This will be tunnelled to multicast exit points
     5. Inner header will not have a MPL option
 4. The alternative to (3) is to use link-local mc address in
    conjunction with a MPL option:
     1. Encapsulated
     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
     3. Outer header will have a MPL option
     4. Inner header will have site local mc address (e.g. FF05-based).
        This will not be tunnelled as it is recapsulated every hop
     5. Inner header will not have a MPL option