Subject: RE: [Mipshop] FMIPv6 - NAR sets up tunnel endpoint?

From: "GAABAB Brahim RD-CORE-CAE" <[email-masked]>
Date: Thu, 8 Sep 2005 10:20:28 +0200

Alex, comments inline.

> De : Alexandru Petrescu 
> 
> GAABAB Brahim RD-CORE-CAE wrote:
> > Hi Alex,
> > 
> > I think there is a misunderstanding here. Should read it like this :
> > "The NAR MAY also set up a reverse tunnel to the PAR in 
> this case.", i.e. when no NCoA can be assigned to the MN.
> 
> Right, I have read it too quickly previously.  The host route 
> and NAR-PAR tunnels are set up when the NCoA is impossible to 
> be assigned.
> I hope in that case the tunnel endpoint on PAR points to NAR 
> (instead of pointing to NCoA).

Right.

> 
> > I agree that the spec should be more clarified..
> 
> Maybe clarification about the fact that PAR-NAR tunnels are 
> possible as well as PAR-MN.

The only tunnel described in the spec is just between pAR and nAR. Until
the MN configures a valid nCoA, communications is as follows :

          MN (uses pCoA)------------ nAR
===================================== pAR-----Internet
  (1)                                --> tunnels from pCoA to pAR

  (2)       uses hostroute for pCoA <--

This is said explicitly in bottom of page 26, section 6.2.2
"  The NAR MAY provide support for PCoA (instead of accepting or
   assigning NCoA), establish a host route entry for PCoA, and set up a
   tunnel to the PAR to forward MN's packets sent with PCoA as a source
   IP address."

  (3)                                         tunnels packets for pCoA
to nAR <--
However, the step (3) is not explicitly mentioned. Furthermore, does the
nAR use 0 or 1 for the status flag of Hack ? I think that in case when
no nCoA can be assigend (even the proposed nCoA), the spec is not
explicit.

> 
> Also clarification is needed about the use of host-route.
> 
> Alex
> 

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---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 08 Sep 2005 19:50:57 +0200

GAABAB Brahim RD-CORE-CAE wrote:

>>> I think there is a misunderstanding here. Should read it like
>>> this : "The NAR MAY also set up a reverse tunnel to the PAR in
>> 
>> Right, I have read it too quickly previously.  The host route and
>> NAR-PAR tunnels are set up when the NCoA is impossible to be
>> assigned. I hope in that case the tunnel endpoint on PAR points to
>> NAR (instead of pointing to NCoA).
>
> 
> 
> Right.

Actually, reading further through the draft I find that NAR establishes
a host-route to PCoA also when MN sends FNA with an address that is
acceptable ("When the NCoA corresponding to the FNA message is
acceptable, the NAR MUST ... enable the host route entry for PCoA, if
any is present.")

I am completely lost: NAR MAY set up host-routes for PCoA if the NCoA
can not be allocated after HI and MUST set it if MN proposes a usable
NCoA in FNA.

> The only tunnel described in the spec is just between pAR and nAR.

First par on page 7 has "reverse tunnel between the MN and the PAR", so
the tunnel between pAR and nAR is not the only one, there is also the
possibility of tunnel between PAR and MN.

This is ambiguous and may be critical.  A tunnel endpoint on PAR should
precisely specify which is the other tunnel endpoint.  If it specifies
NCoA as other tunnel endpoint then it will forward packets to NCoA and
only the MN receiving it can decapsulate it, NAR will not decapsulate
that packet because the destination address of that packet is not any of
the NAR's addresses (NAR will try to just forward, not decapsulate).

> Until the MN configures a valid nCoA, communications is as follows :
> 
> MN (uses pCoA)------------ nAR =====================================
> pAR-----Internet (1)                                --> tunnels from
> pCoA to pAR
> 

Sorry I can't see the diagram... (white-space formatting may be why).

> 
> This is said explicitly in bottom of page 26, section 6.2.2 "  The
> NAR MAY provide support for PCoA (instead of accepting or assigning
> NCoA), establish a host route entry for PCoA, and set up a tunnel to
> the PAR to forward MN's packets sent with PCoA as a source IP
> address."

I agree it is said that NAR may install a host route for PCoA towards
its wireless interface.  As I said on the mail titled "NAR sets up host
route": when is that route deleted?  when is the similar route on PAR
deleted?

> to nAR <-- However, the step (3) is not explicitly mentioned.
> Furthermore, does the nAR use 0 or 1 for the status flag of Hack ? I
> think that in case when no nCoA can be assigend (even the proposed
> nCoA), the spec is not explicit.

It's the "Code" field of HAck, nor "status", right?  I think it should
use value a new value, 5, "Handover Accepted, NCoA not accepted and not
assigned".

Alex