Subject: Re: [mobile-ip] MIPv6 Issue 120: Mobile Prefix Advertisements

From: [email-masked]
Date: Mon, 21 Oct 2002 12:02:34 +0530

>
> > 1) Do we need to wait for any acknowledgement of MPA that is sent in
> > response to MPS ?
>
> 10.10.2 says that the home agent waits for an ack in the form of a BU
> with the new address or an MPS.
> 11.4.2. says that the mobile node uses the same retransmission
> procedure for MPS as for BUs.
>

The draft says -
"The home agent SHOULD periodically continue to retransmit an unsolicited
Advertisement to the mobile node, either until it is acknowledged by the
receipt from the mobile node of a Binding Update with a home address
matching the new home prefix in the packet, or until the home agent
receives a Mobile Prefix Solicitation from the mobile node. "

1)  It talks about retransmissions in case of "unsolicited Advertisements
to MN".

2)  In which case MN will send BU as an ack to MPA and in which case it
will send MPS in response to MPA ?

3)  What is meant by "receipt from the mobile node of a Binding Update with
a home address matching the new home prefix in the packet" ?

Suppose the advertisement sent due to change in valid lifetime of a
particular prefix A. Then the HA will send all the prefix information
options in the MPA to MN. And the BU from HA will contain the Home address
with the prefix A. What should be state of the flags 'S' and 'L' ?
What if there is a change in paramaters of more than one prefix ?

- Sourajeet

----------------------------------------------------------------
Sourajeet Mohanty
Software Engineer
Communications and Embedded Systems
L&T Infotech Ltd., Bangalore
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From: Jari Arkko <[email-masked]>
Date: Sat, 26 Oct 2002 09:23:19 +0300

> will send MPS in response to MPA ?

In Section 11.4.3 of the latest draft on the web there's a MAY where
the mobile node can choose to either accept the advertisement as is,
or send a solicitation. So thats the decision point. Presumably it
is up to the mobile node's policies whether to use BU or MPS followed
by BU.

The MAY clause wasn't quite correct in the posted version, so here's
the text I have on it now:

    For advertisements that do not contain the same ICMP Identifier
    value as in a recently sent solicitation, the mobile node MAY
    send a solicitation and expect an advertisement with a matching
    Identifier before further processing.

> What if there is a change in paramaters of more than one prefix ?

I suppose the flags should be as they normally are in BUs. What
if had an S=0 "multi-binding" which was sent using home address HoA1,
and implicitly for HoA2 & HoA3. Then we assume HoA2 prefix is somehow changed
and this change is communicated to the mobile node. The mobile node
will then send an S=0 re-registration, say again with HoA1. Is this
an acknowledgement? The current text isn't specific enough for this
case.

So lets think about this in depth this time. What are the potential
modifications?
- new prefix
- removed prefix
- changed prefix

When do we consider a BU to acknowledge the unsolicited MPA? I would
propose the following:
- A BU is received for one of the modified prefixes
- "One" above means receiving at least one BU; we leave it to the
   mobile node to send the rest if it needs to, now it at least knows
   about the change
- The above applies both to new prefixes (BU=reg), changed prefixes (BU=dereg)
   and changed prefixes (BU=rereg)
- "BU is received for" applies whether the home address is specifically
   given in the BU or implicitly determined through S=0

If this is acceptable, here's the proposed text:

    The home agent SHOULD periodically continue to retransmit an
    unsolicited Advertisement to the mobile node, until it is
    acknowledged by the receipt of one of the following messages
    from the mobile node:

    - A Mobile Prefix Solicitation.

    - A Binding Update for any home address with any of the
      modified prefixes. The modification can be the addition
      of a new prefix, the deletion of an existing prefix, or
      some other change in the information regarding the prefix.

      Note that the Binding Update is considered to be for a
      specific home address either because the home address
      was explicitly given in the message, or because it was
      implied through the use of the Single Address Only (S)
      bit.

Jari