Subject: Re: [mobile-ip] Draft on Mobile IP Architecture and Reorg

From: Alper Yegin <[email-masked]>
Date: Sun, 02 Mar 2003 19:36:54 -0800

> Pekka Nikander and I wrote a draft on separating out Mobile IP along the
> architectural boundaries of global v.s. local link routing changes. The draft
> is
> draft-kempf-mobileip-arch-00.txt. This draft was primarily intended as a
> recommendation on the upcoming reorg of Mobile IP, which will be discussed at
> the NSIIM BOF.
> 
> The draft makes a recommendation for taking all the work currently involved in
> local link routing (CARD in Seamoby, ODAD, FastRA, FRA, etc. in IPv6, and
> FMIPv6
> in Mobile IPv6) and grouping them together into a separate working group with
> a
> tightly focussed charter based on architectural considerations, so that any
> changes to RFC 2461 and 2462 are well-designed and co-ordinated.

Thanks James, for initiating this discussion.

I'd think such a WG would be named "Fast Handovers for IPv6", right?
CARD, FastRA, oDAD are meant to benefit general IPv6 users as well,
not only FMIPv6 users. But the above collection gives me the impression that
the focus is "FMIPv6". And you want to bring together other components that
FMIPv6 might benefit from. Is that the right characterization of your
proposal?

Some comments on the draft:

   The local routing problem consists of two parts:
    
  1) The need for a mechanism by which the Mobile Node obtains a new
     care of address on a new link,

This is really "simple network access" problem with IPv6.

  2) The need for a mechanism to temporarily repair the local routing
     failure due to a switch in link prior to the change in global
     routing at the Home Agent (and, in route optimized, Mobile IPv6
     Correspondent Nodes) taking place.

One way to see this is "sometimes local routing fix can (temporarily)
substitute global routing fix"

   Localized mobility management does not address reducing the amount
   of time required for the Mobile Node to detect that is has moved ...

It doesn't, neither does any of the other methods. This can be handled by L2
triggers ....

   At the extreme, a regional routing proxy may be required
   for every subnet [for LMM approach], like a Foreign Agent, or for every
   aggregation router serving a collection of subnets through a low capacity
   edge link, like a T1 line.

Other methods are already at this "extreme".

   Because both the mechanism and expected deployment pattern of the
   regional routing proxy involve mechanisms more similar to the global
   Mobile IP architectural elements, "localized" mobility management
   should more properly be called "regionalized" mobility management,
   and therefore regional routing proxies are more properly considered
   part of the global, not local, Mobile IP architecture.

I don't quite follow this. To some extent, all these methods have Mobile IP
architectural element, that is binding an IP address to another one for
redirecting traffic.

   From the design, it is entirely
   unclear why the old access router is privileged with respect to
   starting the tunnel.

Because this is so much like "Mobile IPv6" as in forwarding from previous
care-of address, so it is a natural choice.

  The 
   global routing proxies scale like servers, in the sense that
   reliability depends on multiple expensive, very reliable nodes with
   highly replicated state so that the unlikely failure of one node
   requires a hot standby to quickly take over. The local routing
   scales like routers, in the sense that reliability depends on
   multiple, cheap nodes with replicated functionality and minimal
   replicated state so that routing fails over automatically with
   minimal to no host involvement.

I disagree with this characterization. Looking at the method proposed, there
is no fundamental difference between the Home Agents and enhanced routers
assisting these fast handovers. I don't think one can be so complex and the
other so simple. And I cannot follow the logic that leads to:

   This suggests that the signaling for mitigating local routing
   failure should be derivative of the local link signaling in RFC 2461
   rather than the global signaling used with the Home Agent and
   Correspondent Node.

alper

---

From: "Nick 'Sharkey' Moore" <[email-masked]>
Date: Mon, 3 Mar 2003 18:08:57 +1100

On Sun, Mar 02, 2003 at 07:36:54PM -0800, Alper Yegin wrote:
> not only FMIPv6 users.

True, true, OptiDAD was drafted to be independent of the whole MIP
thing, and it's conceivably useful to have quick handovers without
everything else, for example if L4 is tolerant of changing IP addresses
(yeah, yeah, I know, L4 mobility isn't a good idea for many things).

Actually, maybe this whole MIP thing splits most easily into:

* fast handovers (predictive, non-predictive, maybe L2 dependant)
* MIPv6 Route Repair (signalling to HA/CN/MAP/whatever)

(And then route repair can be split again as per James' suggestions.)

The advantage of this split is that it makes it quite clear that 
handover optimizations are outside the scope of MIPv6 ... which
still leaves a MIPv6 useful for web browsing, ssh sessions, etc 
without introducing a whole lot of optimization weirdness.

-----N
-- 
Nick 'Sharkey' Moore  <[email-masked]>  <http://zoic.org/sharkey>
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