Subject: Re: [MOBILE-IP] MIPv6 node location detection

From: "Hesham Soliman (EPA)" <[email-masked]>
Date: Sat, 14 Oct 2000 00:41:45 +1100

> What is the difference between two advertisement below ?
>       - Renumbered home link router advertisement
>       - Router advertisement in a foreign link
>
> My question is why the mobile node don't just add the new address
> in MN's address list. How do the MN decide whether it start MIPv6
> process or autoconfiguration process for renumbered home link address.
> What if the all home addresses in the list have expired before the MN
> get FA's router advertisement, can the MN still use the expired address
> record
> in it's system ?
>
        => I think you're certainly asking the right question but
        perhaps to the wrong mailing list :)
        If I understand you correctly, you're saying that while the
        MN is at Home, if a new advertisement is received with a new
        prefix, how does it know that this is not another foreign subnet.
        Well based on my rusty knowledge  of ND and stateless address
        configuration, it doesnt know. But I don't think that this is
strictly
        a MIP issue. While you're at home MIP does not do anything
        for  you. So that's why I'll cc IPng on this to see if someone can
        give you a better answer, or maybe I missed something here.
        BTW FA's do not exist in MIPv6.

> I also can't find RFC or draft which define exactly address list in a
> MIPv6 MN. A IPv6 node have a address list and  every prefix has lifetime.
> Please give me some advice on it.
>
>
>

---

From: "John F. Leser" <[email-masked]>
Date: Fri, 13 Oct 2000 10:14:26 -0400

>         BTW FA's do not exist in MIPv6.

Reading through section 10.4 of the MIPv6 draft (version 12), I get the
impression that:

1. Movement detection is not a simple problem to solve.  The draft
doesn't really specifiy what method should be used.

2. Seeing an adverisement from a router with a different prefix is not a
good way to detect movement.  The preferred movement detection method
seems to be loss of reachability of the MN's default router, which is
noticed through neighbor unreachability detection and/or use of the
router advertisement interval option.

> > Please give me some advice on it.

You may want to take a look at section 5.2 of RFC 2462, which mentions the
address list.  I hope this is helpful.

-------------------------------------------------------------------
John Leser                      UNH InterOperability Lab
IP/Routing Consortium Engineer  Morse Hall, 39 College Rd, Room 332
Tel: (603) 862-0090 (8-5 EST)   Durham, NH 03824-3525
Fax: (603) 862-1761             Web: www.iol.unh.edu
-------------------------------------------------------------------

---

From: Lars Henrik Petander <[email-masked]>
Date: Sat, 14 Oct 2000 11:30:22 +0300

On Fri, 13 Oct 2000, John F. Leser wrote:

> good way to detect movement.

That depends whether you are keeping a list of the known routers. If you
have a list of all known routers and you hear an advertisement from a new
router, which is not on the list, then you have probably moved.

This gives you the possibility of making a handoff before losing contact
with your current router. Of course the list needs to be purged of routers
that have been unreachable for some time. This scheme works well if the
user moves linearly, but requires router unreachability detection in other
cases.

> The preferred movement detection method

Neighbour unreachbility detection is somewhat slow due to the default
timer values. Also frequent sending of RAs has some downsides, e.g., heavy
processing and bandwidth costs. Since the handoff takes place only after
losing the default router, some packets may be lost.

Based on my experiences developing the movement detection part of the MIPL
implementation, a combination of eager cell switching that is moderated by
the list of known routers combined with router unreachbility detection
based on the router interval option works well in most cases.

Henrik Petander

---

From: Francis Dupont <[email-masked]>
Date: Tue, 17 Oct 2000 16:15:29 +0200

In your previous mail you wrote:

=> there are many different methods, some of them are (too) slow,
some of them can detect movements when there is no movement, this can
be a problem or not... I think we need to get results from fast/smart/...
handoff special group and from implemention experiences.

=> I agree but the other way is not better.

   The preferred movement detection method seems to be loss of
   reachability of the MN's default router,

=> this is not good if there are more than one router and of course
is very bad if the number of potential default routers is large enough...

   which is noticed through neighbor unreachability detection

=> which uses neighbor solicitations, not router solicitations !

   and/or use of the router advertisement interval option.

=> this point should be added into neighbor discovery specs (ie.
it is useful in general, not only for mobility).

   > > MIPv6 MN. A IPv6 node have a address list and  every prefix has lifetime

=> in *theory* the list is the union of local prefixes and home prefixes,
both are in router advertisements on the local link and through the tunnel
with the home agent with the according lifetimes. In order to get the whole
list ASAP someone suggested in this list that the home agent sends router
advertisements to the MN when a home registration is done.

The issue is what happens if the home link is renumbered when the MN is
stopped. In fact this depends on how the MN knows its home prefix(es):
 - very stupid implementations believe the MN is started at home then
   the home prefixes will be prefixes of the first attached link: no
   problem with renumbering.
 - stupid implementations use a static config in order to know home
   prefixes then if the config is too old the MN will not be able to
   find its home link (and a home agent).
 - someone suggested in the list to use a name which can be updated
   when the home prefix is renumbered (but not renamed :-). It is a
   fine idea out of the scope of the mobile IPv6 draft.
I think most implementations use the second way (static config)...

An open question is what to do with DHCPv6?

Regards

[email-masked]

---

From: Francis Dupont <[email-masked]>
Date: Tue, 17 Oct 2000 16:24:19 +0200

=> this works well in an environment where mobility is some kind of
cellular thing. There are other types of movements, some of them
very easy to detect like physical interface (ex)changes. Someone
proposed the final solution: use PPP and bring it down and up
during movements (not more silly then anything is cellular :-).

Regards

---

From: Thomas Eklund <[email-masked]>
Date: Wed, 18 Oct 2000 11:34:18 +0200

Hi some commente regarding the movement detection algorithm.
I agree that it might not be a good idea to tie your movement detection to
when you are seeing an advertisement from a router with a different prefix.

First of all - the statemachine for the movementdetection can be at two
places - either in the 1) mobile node (which is the case today) or 2) it can
sit in the network and then you could have network controlled handoff.

To improve handoff you must make increase mobile IP's link-layer awarness.
This is usually achived by listening on the field strengh or something
similar of the radio link. The solution is different for every different
radio link you have.

Take 802.11 ethernet for instance, there you can associate every radio cell
(and AP) to an IP subnet with a new prefix or you can associate several AP
to an IP subnet (recomended). In case 1) you can associate every radio cell
with a subnetprefix and you modify you movement detection algoritm (MDA) so
that it builds up an internal list with prefixes and subnet and associated
field strengh.

For instance:
General Parameters:
Joning treshsholds: xxx dBm
Leaving Treshholds: xxx dBm

CoA        Current Subnet   Field strengh  Active CoA
CoA1         Prefix 1                   xx dBm           ---
CoA2         Prefix 2                   xx dBm        Active
CoA3         Prefix 3                   xx dBm           ---
CoA4         Prefix 4                   xx dBm           ---
CoA5         Prefix 5                   xx dBm           ---

The intention is also to start bulding new CoA before you must switch over
to a new AP which will make you handover quicker. You listens on the field
strengh of the different radio cells or subnets and associate make you
handover based on the field strengh.

This approach could also be done from the AP or BS which would be a good
aproach o a WAN radio like GSM or CDMA. Then the movement detection
algorithm sits (it is not called that in GSM terms) in a BSC and in tells
you to do you handover but in this case you would have to interupt that let
mobile IP have that info and then mobile IP could be invoked in network
initiated handoffs. This is nice on paper and would really optimize the
radio network for IP but there is a lot of polotics here which can make it
very difficult.

You can also include QoS parameter in your handover design and you can make
it very advanced.

In other it is nothing in the spec that stops you from achieving very good
handoffs.

-- Thomas Eklund

----- Original Message -----
From: "Francis Dupont" <[email-masked]>
To: "John F. Leser" <[email-masked]>
Cc: <[email-masked]>; <[email-masked]>
Sent: Tuesday, October 17, 2000 4:15 PM
Subject: Re: [MOBILE-IP] MIPv6 node location detection

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---

From: "John F. Leser" <[email-masked]>
Date: Wed, 18 Oct 2000 11:10:50 -0400

> similar of the radio link. The solution is different for every different

[cut]

I don't doubt that there are many ways the link layer could provide
excellent movement detection.  I think the issue here is how to provide
some movement detection for MIPv6 without any special signalling from
lower layers.

I think you did touch on an important point - movement detection is really
two problems - (1) detecting movement on to a link, and (2) detecting
movement off of a link.  If the mobile node is eager to move to new
networks, then it is only critial that (1) take place quickly for smooth
handoffs.  Its somewhat less clear to me when (2) must take place, but it
should happen eventually.

With this in mind, I'd like to suggest this as an idea for movement
detection:

- Require that a home agent's router advertisements always contain all
of the prefixes on the network that are valid for home or CO addresses.

- Then, whenever a MN receives an RA with the H bit set, it will know
with certainty whether that RA came from the current home or foreign
network, or from some new network, based on whether the prefix of the MN's
home or current CO address is advertised in the RA.  This way, movement
onto a new link is detected as soon as any home agent on that link sends
an advertisement.

- Whenever an RA is received indicating movement onto a new link,
the MN transitions neigbor cache entry for the old default router(s) to
stale, to accelerate unreachability detection.

Of course, the danger here is that the network could be misconfigured so
that home agents are not advertising all prefixes.  This would be
sub-optimal (mobility would be uses when it is not needed), but wouldn't
prevent the mobile node from communicating.

I'm curious what people think of this.

---

From: "Charles E. Perkins" <[email-masked]>
Date: Wed, 18 Oct 2000 08:39:29 -0700

Hello John,

I've been unable to keep up with the general discussion on
this issue, but I've scanned through many of the messages.
I think this is an issue that should be resolved in the next
(and perhaps _last_ before Proposed Standard) revision of the
Mobile IPv6 protocol specification, which is coming imminently.
Thus, I'd like to find out if we can get to some agreement on
whatever clarifications or enhancements are needed.

> some movement detection for MIPv6 without any special signalling from

Agree.

> of the prefixes on the network that are valid for home or CO addresses.

seems to solve the problem with least harm.  I particularly think
it compares well with another alternative which was suggested,
according to which the mobile node would have to assume that every
advertising home agent was its own home agent.  I think the strategy
above will introduce less traffic on the wireless link.

I also agree with previous statements that renumbering should happen
gently.  In the context of your suggestion, this would mean that the
deprecated prefix would be carried by agent advertisements for quite
a while.  I think that whatever is specified in the Neighbor Discovery
draft SHOULD cover the required time durations for deprecated addresses,
but I didn't go check the wording before sending this message.  If it
is not sufficient there, then we should make some explicit parameter
value specifications in the Mobile IPv6 draft.

> stale, to accelerate unreachability detection.

Agree.  And, if your strategy is adopted, I reckon the draft should
explicitly state this.

> prevent the mobile node from communicating.

A lot of things can go wrong if the network is misconfigured!

Maybe we can put mandatory requirements in the draft so that such
misconfigurations go against explicitly stated MUSTs.  Your help
in determining some correct wording would be appreciated.

Regards,
Charlie P.

---

From: Francis Dupont <[email-masked]>
Date: Fri, 20 Oct 2000 14:09:29 +0200

=> according to other messages your idea is to overload the meaning
of the H flag with "this RA announces all the prefixes"...
I don't think it is a good idea but if to know the number of prefixes
(there are some optimizations where this info is needed) is very useful
then why not a new extension with it in any RA?

=> this is not protected against a rogue RA and doesn't work with
overlapping cells (which seems to need the help of the layer two).

=> move the state to incomplete is more aggressive (faster but more
expensive if there is no real movement).

=> I think to rely on RAs for movement detection is not very good because
if this should be fast then the frequency of RAs has to be very high
(ie. higher than reasonnable). And this is dedicated to a very special
scenario (the cellular one) when there are many of them. In this list
(mobile IP) many of us did shout that cellular != wireless != mobile,
please add me...

Regards

PS: the only very clear indication you can get from a RA is to receive
an announce for the home prefix(es) where you are in visit. In other
cases you can only suspect a movement.