Subject: [mobile-ip] FMIPv6 : Triggering of tunnel establishment

From: "Suvidh Mathur" <[email-masked]>
Date: Thu, 7 Aug 2003 18:20:42 +0530

Hi,

Reading the fmipv6 draft 06, one change I noticed is the triggering of HI /
HACK exchange
between ARs. Draft 06 requires HI / HACK exchange to be initiated after
receiving an
FBU from MN. Though the reason for this is clear, I do have some doubts
about it:

   1. If stateful address configuration is used at NAR, until NAR allocates
NCoA and
         sends it in HACK message, the PAR is not aware of the NCoA. In
such a scenario,
      PAR would not be in a position to send NCoA in PrRtAdv, and
subsequent FBU /
      FNA sending from MN would also be done without MN knowing the NCoA.

   2. For packet buffering at PARs, the draft specifies "When the PAR
receives an FBU,
      it MUST send a HI message to the NAR. Upon receiving a corresponding
HACK
      message, the PAR MUST send FBACK to the MN. Until the HACK is
received,
      the PAR MAY buffer any packets arriving for the MN."

      In this case, if MN sends FBU after attaching to the new link then
      there would be
      some packet loss which can be avoided if AR starts buffering on
      receipt of RtSolPr.

   3. For buffering at NAR, the draft specifies "The New Access Router MUST
NOT
      tunnel packets from the MN with PCoA as source IP address destined
for arbitrary
      correspondent nodes to PAR until a HI message is received, and the
NAR MAY
      buffer any such packets."

      What would be the trigger for NAR to start buffering?

Regards,
Suvidh

---

From: Rajeev Koodli <[email-masked]>
Date: Thu, 07 Aug 2003 13:44:37 -0700

Hello Suvidh,

>       FNA sending from MN would also be done without MN knowing the NCoA.

Right. However, the MN could "propose" a NCoA in FBU, which is then
carried in HI. The NAR can allocate a new one or okay the proposed one.
The result is indicated in FBack. Note that even if PrRtAdv provided NCoA,
the binding is not complete until FBack is received. When the allocated NCoA
is different compared to the proposed NCoA, FBack should contain the allocated

NCoA.

>       some packet loss which can be avoided if AR starts buffering on

When PAR should start buffering is a good question. If RtSolPr is sent just
before handover, this should work fine. However, the very same event that
allowed RtSolPr to be sent anticipating an impending handover could also
serve as trigger to send FBU. So, the general problem is: how does the MN know

it is moving ? Because of this and other reasons, we separated the Proxy
Router messages
from the actual handover timing. In any case, the MN should be able to send
them
any time. So, if an option to request buffering is desirable in RtSolPr,
I suppose we
could add that.

>       What would be the trigger for NAR to start buffering?

There has been some discussion on this leading to the following. The MN would
tunnel directly to PAR instead of requring NAR to do tunneling. In fact, the
tunnel termination and begining will happen at the MN instead of at NAR. So,
3) should not be an issue anymore.

Thanks,

-Rajeev