Subject: RE: [nemo] RFC 3963: Clarifications if the MR is MN too

From: "Pascal Thubert \(pthubert\)" <[email-masked]>
Date: Wed, 11 May 2005 09:08:03 +0200

As I remember, the intent is that:

1) The Home address is a unique id for a registration. 

2) R bit and ~R bit are mutually exclusive. So a binding is for either
one but not both. NEMO says:  
	If the Mobile Router has a valid binding cache entry at the Home
   Agent, subsequent Binding Updates for the same Home Address should
   have the same value as the value in the binding cache for the Mobile
   Router Flag (R).

In other words, if a MN needs to maintain 2 bindings, then it needs 2
home addresses. This would be the only way to have both types of
binding.

3) A MR that binds with R bit is reachable at its home address with the
full service set of an MN. R bit only adds functionality to the MRHA
tunnel.

4) NEMO basic does not cover route optimization. So the behavior of a HA
should a CN attempt RR test for an MR binding is undefined. I suspect
that by default, most implementations would act as if the MR was a MH. 

To answer a specific question from the original mail, the term "Mobile
Node" is inherited from RFC 3775. When RFC 3963 says Mobile Node, it
means as defined by RFC 3775. The term Mobile Host was previously
undefined and we used it in NEMO to point out the difference. But an RFC
3775 Mobile Node is really a Host and I agree it's misleading.

The Cisco implementation supports concurrent bindings for MRs and MNs
but a single binding per Home Address.

Do I miss anything?

Pascal

| -----Original Message-----
| From: [email-masked] [mailto:[email-masked]] On Behalf
Of
| Thierry Ernst
| Sent: Wednesday, May 11, 2005 8:12 AM
| To: [email-masked]
| Subject: Re: [nemo] RFC 3963: Clarifications if the MR is MN too
| 
| 
| Hi,
| 
| Yes, the HA supports both operation, but I think the question is
| about doing this simultaneously.
| 
| On the MN side, the current text in RFC 3963 doesn't mean the MN can
act
| simultaneously both as a MH and a MR ; and, if it does, does it need
to
| send only 1 BU or 2 BUs.
| 
| I think the authors of the RFC should clarify this point (i.e. what is
| the correct interpretation, from an implementation point of view, of
the
| possibility for a MN to act both as a MH and a MR).
| 
| Thierry
| 
| 
| > > The RFC 3963 says in:
| > >
| > > (1) Section 3, p5 "When the Mobile Router moves away from the home
| > > link and attaches to a new access router, it acquires a Care-of
| > > Address from the visited link.  The Mobile Router can at any time
| > > act either as a Mobile Host or as a Mobile Router. It acts as a
| > > Mobile Host as defined in [1] for sessions it originates and
| > > provides connectivity to the Mobile Network.  As soon as the
Mobile
| > > Router acquires a Care-of Address, it immediately sends a Binding
| > > Update to its Home Agent as described in [1]. When the Home Agent
| > > receives this Binding Update, it creates a cache entry binding the
| > > Mobile Router's Home Address to its Care-of Address at the current
| > > point of attachment."
| > >
| > > (2) Section 4.1, p7 "A new flag (R) is included in the Binding
| > > Update to indicate to the Home Agent whether the Binding Update is
| > > coming from a Mobile Router and not from a mobile node.  The rest
of
| > > the Binding Update format remains the same as defined in [1]."
| > >
| > > (3) Section 4.1, p7 "Mobile Router Flag (R) The Mobile Router Flag
| > > is set to indicate to the Home Agent that the Binding Update is
from
| > > a Mobile Router. If the flag is set to 0, the Home Agent assumes
| > > that the Mobile Router is behaving as a Mobile Node, and it MUST
NOT
| > > forward packets destined for the Mobile Network to the Mobile
| > > Router.
| > >
| > >
| > > Assuming that a MR is MN too, as described in (1), my questions
are:
| > >  - (2) seems to indicate that such a MR has to send 2 BU: one with
| > > R=0 for MIPv6 and one with R=1 for MIPv6. Am I wrong?
| >
| > In our implementation one R-BU is sufficient to "bind" both the HoA
| > and the complete MNP.  It was not in the intention to have two BUs
| > sent one for MH and one for MR.
| >
| > > - (3) seems to indicate that a HA cannot manage NEMO and MIPv6. Am
I
| > > wrong?
| >
| > Terminology-wise, "If the flag is set to 0, the Home Agent assumes
| > that the Mobile Router is behaving as a Mobile Node" should probably
| > better say "Mobile Host" instead of "Mobile Node".  That would
clarify
| > things I believe.
| >
| > Implementations that I know of have a HA that either supports MH or
| > both MH/MR (a MN is an MH and MR actually, by the RFC3775
definitions
| > I believe).

---

From: Thierry Ernst <[email-masked]>
Date: Wed, 11 May 2005 17:23:44 +0900

>    have the same value as the value in the binding cache for the
>    Mobile Router Flag (R).
> 

Make sense. Shouldn't this be enforced, and clarified in the spec ?

I mean, the question raised in this thread clearly shows that
implementers don't know how to interpret the spec.

> 3) A MR that binds with R bit is reachable at its home address with
> the full service set of an MN. R bit only adds functionality to the
> MRHA tunnel.

That's the point.

> 4) NEMO basic does not cover route optimization. So the behavior of a
> HA should a CN attempt RR test for an MR binding is undefined. I
> suspect that by default, most implementations would act as if the MR
> was a MH. 
> 
> undefined and we used it in NEMO to point out the difference. But an
> RFC 3775 Mobile Node is really a Host and I agree it's misleading.

Yes, very missleading since the definition of a node is "either a host
or a router", so a MN is either a mobile host or a mobile router per
definition. But RFC 3775 is only about MH. May be the revised RFC 3775
should change the wording too.

> but a single binding per Home Address.

What do you mean, using 2 HoAs then ?

> Do I miss anything?

Thierry