Subject: Re: [nemo] summary of same MNP to mutliple MRs discussion

From: Mattias Pettersson <[email-masked]>
Date: Wed, 07 Apr 2004 10:09:16 +0200

Hi Vijay,

Vijay Devarapalli wrote:
> it took me a while to go through the entire thread. I
> am not sure what the problem is. the problem kept
> shifting. :) here is a summary (from what I understood).

Same happened to me. Now I'm through. :)

> 
> first of all, the current spec prevents assigning the
> same MNP to two mobile routers _if required_. it depends
> on what is configured in the Prefix Table on the Home
> Agent. if the Prefix Table on the Home Agent says that
> a particular MNP was given out only to MR1, the Home
> Agent sends a binding ack with status 142 to MR2 when
> MR2 sends a BU to the Home Agent.
> 
> if the Prefx Table says both MR1 and MR2 are authorized
> for a MNP, then it _is_ possible for both MR1 and MR2
> to register with the Home Agent with the same MNP at
> the same time. the HA then has two routes to the MNP,
> one route pointing to MR1 and the second pointing to MR2.
> this is what Hesham is talking about. the current NEMO
> basic support spec works in this case.

And it is made clear that this is supported?

I think we need to tie in the discussions in issue 34.

If an IGP is used, then the IGP will manage the routing table and create 
two entries. If only one HA is used, then the two entries will be in the 
  routing table of this HA, each of them pointing out an HA-MR tunnel. 
If two separate HAs are used, where the two MRs register with one each, 
the IGP will make sure that each HA has two entries: one pointing out 
the local HA-MR tunnel, the other pointing out the other HA.

On the other hand, if no IGP is used, we have to depend on the prefix 
table. I assume it will work when only one HA is in used. When two 
separate HAs are in use, there has to be an out-of-band synchronisation 
of the prefix tables on the two HAs. However, I think this 
synchronisation is out of specification.

> 
> if the Mobile Network splits, with MR1 in one network
> and MR2 in another network, both advertising the same
> MNP and both registered with the Home Agent, then there
> is a problem. Hesham wants this stated in the spec. the
> Home Agent could pick the wrong route.

Yes, but the form of distributed multilink subnet Pascal talked about 
would be a way to keep a split mobile network together.

I think there are good reasons to support both a NEMO with a single MNP 
but multiple MRs, and allow it to split.

> 
> then again, others have argued that if you expect two
> mobile routers which were part of the same Mobile
> Network (but not nested, both have uplinks) to move
> away and split the mobile network into two, it is
> stupid to assign the same MNP to both. each MR should
> be delegated a unique MNP.

I don't think it is stupid.

Basically for the reasons Marcelo stated, I see a clear case for a 
simple multihomed NEMO, with as little changes as possible to the legacy 
MNNs.

This simple case will, IMHO, include:
- No requirements on MNNs about SAS, DR selection, care about different 
access technologies
- The NEMO may split
- Do not rely upon host multihoming solutions to become RFC

and it is possibly solved by:
- having only one MNP in the NEMO
- letting the MRs and HAs have to see to that this works
- letting the routers handle all routing decisions
- have some form of multilink subnetting to handle the split.
- just provide connectivity and do not differentiate between accesses 
(MNNs won't be able to; MRs and HAs may be able to)

I think Hesham has a much more advanced case in mind.
- moving access selection to the MNNs
   - MNN/end-user responsible for the cost of the access selected
   - somehow propagate available accesses to the MNNs
- differentiate traffic from different apps
- if MR has multiple accesses, MNN must be able to tell MR (and HA) to 
use one specific.

This case puts a _lot_ of new requirements on the MNNs. Possibly legacy 
MNNs can fall back to a simpler case (we should make sure they can, 
which is why I am worried about allowing MRs to advertise different 
MNPs). I don't say that manufacturers of MNNs do not want to endorse 
these additional requirements, but we are primarily lacking a number of 
new protocols here. I fear this is too much for NEMO WG.

> 
> on top of everything we dont have a clear definition
> of what it means when two Mobile Networks merge or split.
> (we are _not_ talking about nesting here). this is
> almost MANET space.

If one MNP is used:

It is very much like multilink subnetting. A subnet that previously 
spanned a single link now spans two separate links. If the two links are 
connected to two router-mode interfaces of a multilink subnet router 
then they can still reach each other and still use the same MNP. Now 
with NEMO, the MLSR will be distributed over multiple MRs, so the each 
MR will have to tunnel traffic to another MR for MNNs that are in that 
MR's partition of the NEMO.

On the other hand, without the distributed multilink subnetting, the 
NEMO is broken, of course.

I would say that this case requires _coordination_ between MRs.

If one MNP per MR is used:

The NEMO essentially consists of two separate NEMOs, just merging their 
ingress links. An MNN may use the MRs of the other NEMO, but it will 
have to implement some form of host multihoming (optionally with session 
continuity support) to deal with SAS, DRS and NEMO split.

I would say that this case _does not_ require coordination between MRs.

/Mattias

---

From: Mattias Pettersson <[email-masked]>
Date: Wed, 07 Apr 2004 10:09:16 +0200

Hi Vijay,

If one MNP is used:

/Mattias

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From: Vijay Devarapalli <[email-masked]>
Date: Tue, 20 Apr 2004 15:40:33 -0700

Hi Mattias,

> And it is made clear that this is supported?

maybe not. but the basic support spec does not prohibit
this. my understanding is that this will be handled in
this WG when multihoming for NEMO is addressed in a
separate spec.

>  routing table of this HA, each of them pointing out an HA-MR tunnel. If 
> two separate HAs are used, where the two MRs register with one each, the 
> IGP will make sure that each HA has two entries: one pointing out the 
> local HA-MR tunnel, the other pointing out the other HA.
> 

okay.

> but multiple MRs, and allow it to split.

distributed multilink subnets sound interesting. I think
we need to look into them separately either in NEMO or
in another WG. but not in the NEMO basic support.

> I would say that this case _does not_ require coordination between MRs.

I think I understand now. it might be a good idea to write up a
draft on this.

Vijay

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From: Vijay Devarapalli <[email-masked]>
Date: Tue, 20 Apr 2004 15:40:33 -0700

Hi Mattias,

okay.

Vijay