[multimob] Some comments on draft-ietf-multimob-fmipv6-pfmipv6-multicast-03

[Stig Venaas <[e-mail]>]

Hi

Here are my comments on the 03 version.

There may be a line that is too long, and there is one case where a
"MUST not" needs to be replaced with "MUST NOT". Please see the idnits.
http://tools.ietf.org/idnits?url=http://tools.ietf.org/id/draft-ietf-multimob-fmipv6-pfmipv6-multicast-03.txt

One thing is unclear to me in 3.3. It says:

    There are two ways to obtain the multicast
    membership of an MN.  First, MAGs may perform explicit tracking (see
    [RFC4605], [RFC6224]) or extract membership status from forwarding
    states at node-specific point-to-point links.  Second, routers can
    issue a general MLD query at handovers.  Both methods are equally

Are you assuming point-to-point links in this second case? If not,
then I don't see how the PAR can find out the MNs subscribed groups
just by doing an MLD query.

Also wondering if it should be pointed out here that it's not just
groups. For SSM it would be (S,G) or channels. I see it says
groups/channels many other places though. It might be worth explaining
what the term channel means.

    applicable.  However, a router that does not operate explicit
    tracking needs to query its downstream links after a handover.  The
    MLD membership information then allows the PAR to know the multicast
    group subscriptions of the MN.

    In predictive mode, the PMAG (PAR) will learn about the upcoming
    movement of the mobile node.  Without explicit tracking, it will
    immediately submit a general MLD query and receive MLD reports for
    the subscribed group(s).  As displayed in Figure 4, it will initiate
    binding and context transfer with the NMAG (NAR) by issuing a HI
    message that is augmented by multicast contexts in the mobility
    options defined in Section 5.3.  NAR will extract multicast context
    information and act as described in Section 3.1.

In 4.2.2 it says "it MAY need to issue". I don't think this is the
appropriate use of MAY. It's not like MAY implement, or MAY do
something. There is no freedom of choice here. Whether it is done or
not just depends on the situation. I think you could replace "MAY"
with "will".

In 5.3 it says:

    Length: 8-bit unsigned integer.  The size of this option is 8 octets
    including the Type, Option-Code, and Length fields.

How can this be 8 octets. It looks like 4 octets when including the
reserved field, and then the total length varies with the size of the
report payload? But I guess the payload is always at least 4 octets?

In 5.4 it says:

    Length: 8-bit unsigned integer.  The size of this option in 8 octets.
    The length is 1 when the MLD (IGMP) Unsupported Report Payload field
    contains no Mcast Address Record.

Should it say "is" like in 5.3, or should 5.4 say "in"? It looks to me
like the length is 4 if there is no payload. Or is the payload at least
4 octets?

In 5.4 it says:
    that are not supported or prohibited in the new access network.  This
    field MUST always contain the first header line (reserved field and
    No of Mcast Address Records), but MUST NOT contain any Mcast Address
    Records, if the status code equals 1.

Should it say this in 5.3 as well?

It might be good to make the IANA considerations more explicit. It would
be good to explicitly specify what the new tables look like.

Stig