Subject: [MOBILE-IP] MIPv6 node location detection

From: SungJin Lee <[email-masked]>
Date: Thu, 12 Oct 2000 10:37:12 +0900

I got confisued while i was reading MIPv6 standards and
have a couple of question with cases like following. The 
It is assumed that the MIPv6 node use stateless autoconfiguration. 
Let me know if  i lost some in MIPv6 and IPv6 RFC.

Q.1   A MIPv6 node moved to foreign link. The MIPv6 node restarts 
        the system there and receives  router advertisements with 
        foreign network prefix.
        
        How do the MIPv6 node detect if it is located in foreign link ?
        isn't it could be normal autoconfiguration as in the home llink ?

Q.2   A MIPv6 node located in it's home link. The node got an IP address
        with stateless autoconfiguration. At a time the router changed the home link
        prefix and multicast the router advertisement with new prefix. 
        After the home link prefix ifetime expired or before the life time 
       expired, it received router advertisement with new prefix. 

       Why doesn't the IPv6 node think it's located in foreign link when it
        received ? isn't it possible the IPv6 node to think it's moved to a foreign
        link and start MIPv6 process ?

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 12 Oct 2000 14:22:58 +0200

>         isn't it could be normal autoconfiguration as in the home llink ?

Before moving save your home address somewhere; now land in a foreign
net, get a new address, compare it to the previously saved and thus
decide you're a foreigner.

>
> Q.2    A MIPv6 node located in it's home link. The node got an IP
>        address with stateless autoconfiguration. At a time the
>        router changed the home link prefix and multicast the router
>        advertisement with new prefix.  After the home link prefix
>        ifetime expired or before the life time expired, it received
>        router advertisement with new prefix.
>
>        Why doesn't the IPv6 node think it's located in foreign link
>        when it received ? isn't it possible the IPv6 node to think
>        it's moved to a foreign link and start MIPv6 process ?

I would relate this to "renumbering".  The draft-12 provides for
renumbering while MN is away and I think that your case might be
enunciated as a particular case of that.

Alex

---

From: SungJin Lee <[email-masked]>
Date: Fri, 13 Oct 2000 21:19:03 +0900

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 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. 

----- Original Message ----- 
From: "Alexandru Petrescu" <[email-masked]>
To: <[email-masked]>
Sent: Thursday, October 12, 2000 9:22 PM
Subject: Re: [MOBILE-IP] MIPv6 node location detection

: SungJin Lee <[email-masked]> writes:
: > Q.1     A MIPv6 node moved to foreign link. The MIPv6 node restarts
: >         the system there and receives  router advertisements with
: >         foreign network prefix.
: >
: >         How do the MIPv6 node detect if it is located in foreign link ?
: >         isn't it could be normal autoconfiguration as in the home llink ?
: 
: Before moving save your home address somewhere; now land in a foreign
: net, get a new address, compare it to the previously saved and thus
: decide you're a foreigner.
: 
: >
: > Q.2    A MIPv6 node located in it's home link. The node got an IP
: >        address with stateless autoconfiguration. At a time the
: >        router changed the home link prefix and multicast the router
: >        advertisement with new prefix.  After the home link prefix
: >        ifetime expired or before the life time expired, it received
: >        router advertisement with new prefix.
: >
: >        Why doesn't the IPv6 node think it's located in foreign link
: >        when it received ? isn't it possible the IPv6 node to think
: >        it's moved to a foreign link and start MIPv6 process ?
: 
: I would relate this to "renumbering".  The draft-12 provides for
: renumbering while MN is away and I think that your case might be
: enunciated as a particular case of that.
: 
: Alex
:

---

From: Alexandru Petrescu <[email-masked]>
Date: Fri, 13 Oct 2000 17:42:37 +0200

>       - Router advertisement in a foreign link

I'm sharing your surprise there's no written differentiation.  It is
so striking that I imagine the authors have already thought of it and
left it as an exercise :-)

Let's say the MN wrongly considers the newly received RA as a
movement, when in fact it was renumbering at home.  It would first
configure a CoA and default route, then try a BU to his HA.  Now two
things can happen here: (1) either the HA is not yet renumbered, so it
will send a Binding Ack or (2) it has been renumbered and is no longer
reachable.  MN will use either the received Binding Ack (1) or HA
Discovery (2) to find out that the HA's prefix is the same as the
initial MN prefix (1) or as the CoA (2).  Surprise, you're at home, so
BU again, this time with zeroed lifetime to remove wrong cache entry.
Thus, renumbering took place and not visiting.

I think this would not work if home net and visited net both renumber
at the same time and take each other's prefixes.

Alex

---

From: Fred Baker <[email-masked]>
Date: Fri, 13 Oct 2000 19:22:49 -0600

I am not the most knowledgeable on the subject, and my betters may correct
me. But I would think this has to be answered in the exchange with the Home
Agent.

First, the Mobile Node has a number of limitations on its knowledge. It
doesn't know its own prefix beyond what it received in a router
advertisement, for example - if the router advertisement has changed
prefix, that may well mean that the device has changed subnet within its
home domain and should just use that address, or as you suggest, it may
mean that somebody is renumbering the network. Since it doesn't know the
site prefix, it cannot distinguish between the home domain (which is larger
than the prefix for a particular subnet) and a foreign domain.

It also has a responsibility. It must keep the Home Agent apprised both of
its own current address and its current care-of address. So if its address
changes, or if a new address is added to its list on some interface, it is
going to have to advise the Home Agent of that.

It is from the Home Agent's response that it will determine what's
happening. If the Home Agent expresses the opinion that it needs to use the
COA, it probably does, and if the Home Agent thinks its address is just fine...

Now, I haven't read the latest specifications to tell you how the Home
Agent expresses that. But I think it is in that context that the
information is going to have to be derived and communicated.

At 10:37 AM 10/12/00 +0900, SungJin Lee wrote:
>Let me know if I lost some in MIPv6 and IPv6 RFC.
>
>        How do the MIPv6 node detect if it is located in foreign link?
>        isn't it could be normal autoconfiguration as in the home llink?
>
>        received? isn't it possible the IPv6 node to think it's moved to a
> foreign
>        link and start MIPv6 process?

---

From: Fred Baker <[email-masked]>
Date: Sun, 15 Oct 2000 18:44:27 -0700

I came up with the answer to your question. It takes some work, but it's
there. Review draft-ietf-mobileip-ipv6-12.txt

One the router advertisements (sections 4.1, 5.6, 5.7, etc), the routers
tell you whether they are willing to be a home agent and/or a foreign
agent. If no neighboring system is willing to be your home agent but there
is a foreign agent, you are roaming. If there is someone willing to be a
home agent but you cannot authenticate with him, your previous home agent
remains your home agent, and you are roaming. If someone advertises that he
will be your home agent and you can authenticate with him, you are at home.

The one thing that bothered me as I read this was an implicit assumption,
perhaps on my part and perhaps on the author's part, that the device has to
somehow come in contact with its home agent as a neighboring device once in
a while. I can think of a number of scenarios in which this may not be true
- imagine a case where you have a telephone mailed to you on the road
because the old one broke. You certainly want to be able to tell the new
phone the old phone's information and have it stick. Or imagine a device
which is permanently roaming - it never actually is at home. You would want
to configure a home agent address somehow. I trust that in these cases the
protocol is not required.

---

From: Fred Baker <[email-masked]>
Date: Tue, 17 Oct 2000 17:01:26 -0700

I got this privately, and Michael is willing to take this discussion public.

At 08:59 AM 10/16/00 -0700, Michael Thomas wrote:
>My general feeling is that for most wireless devices there is no reason
>why the mobile would _ever_ be directly attached to its home subnet
>router. The reason is pretty straightforward: I want my HA to be a fast
>router on housed on a fast network. I definitely do _not_ want it housed
>on my true home network because then I'd have to deal with triangular
>routing through krufty and slow cable/dsl, not to mention not wanting to
>book qos through a last mile technology. The casual security problem will
>still be as much a problem in wireless as it is today. Namely, it will be
>the exception, not the rule.

There are a couple of points to consider here. One is that I tend to think
a lot of the discussion in Mobile IP is oriented around radio networks, and
it's not in the least obvious to me that radio networks are the only use of
it. I'm looking at it for quite another use that could use radios as the
last mile, but requires no radios at all, and runs on a pretty large scale.
So there is a trap we could fall into here that is somewhat worrisome.

Another is largely as Michael says - we want the Home Agent to be somewhere
with enough capacity for huge numbers of things to use it. The "optimized"
routing helps MIP scale quite a bit, which is an important commercial step.
Making the home agents be in routers off in crufty corners of our corporate
attics (the non-radio case) defeats a lot of that. In such cases, we will
want something more central.

I looked through the Hierarchical Mobility draft, and it seems to have the
right mix of things - although I have to say it is more a marketing
statement about the technology ("it is wonderful and Ericcson is applying
for a patent") than a statement about how to do it beyond the need for
another bit; we need quite a bit on the routing aspects of the technology.
But I think there is a simpler approach that scales more nicely.

In DHCP, there is an assumption that there is a DHCP listener on every LAN.
That isn't even close to reality, so in routers there is often a feature
called a DHCP Helper; it receives the DHCP message and forwards it to an
appropriate DHCP server. I submit that having a Home Agent Helper - a
process which picks up messages sent to the home agent anycast address and
tunnels them to somewhere more central - gives you the right mix of scaling
properties and the ability to site home agents appropriately.

Similarly, if a mobile access helper anycast address existed, the local
router could either be that system, or could tunnel messages to it. If
could advise the mobile device of its presence and willingness to act as a
care-of address; the mobile node would give this mobile access point a more
local care-of address, and said MAP would forward messages directed to it
to that more local COA. The only concern I have with putting the COA
directly on the mobile device is the need for someone to forward them
during handoffs, and this would allow for that. It seems like this "helper"
model is not dissimilar to the Hierarchical Mobility model, but simpler.

I can write up a draft if someone is interested to explore that.

---

From: Francis Dupont <[email-masked]>
Date: Tue, 17 Oct 2000 16:19:08 +0200

In your previous mail you wrote:

=> this is explicitely forbidden because many things (not only mobility)
will break if two prefixes are quickly swapped...

[email-masked]

PS: prefixes are not ephemeral, default lifetimes are in days and
renumbering "hold down" in months.

---

From: Francis Dupont <[email-masked]>
Date: Tue, 17 Oct 2000 16:57:33 +0200

At 08:59 AM 10/16/00 -0700, Michael Thomas wrote:
   >router on housed on a fast network.

=> for some other reasons I believe this kind of "virtual" home link will
be common. For instance if mobile IPv6 is used for mobile phones then
the home link will be a set of large boxes inside the core of the operator
and mobile nodes will be *never* at home (in fact the home link doesn't
need to physically exist then I call this a "virtual" home link).

   it.

=> I agree, even the future of IPv6 seems to be 3G mobile phone, my favorite
mobile IP usage is to exchange a 9600bits/s wireless expensive PPP for
a 100Mbits/s free Ethernet. Only mobile IP can do that!

=> you are a bit unfair with hierarchical mobility. This is a good idea
and some proposals are already merged and implemented (ie. it is no more
academic paper or industrial marketing :-).

   appropriate DHCP server.

=> this exists in DHCPv6 as "relays" and multicast can optionally be used
in order to find servers.

   I submit that having a Home Agent Helper - a
   process which picks up messages sent to the home agent anycast address and
   tunnels them to somewhere more central - gives you the right mix of scaling
   properties and the ability to site home agents appropriately.

=> I think the current home agent discovery in mobile IPv6 (which uses
an anycast address in the home prefix) has already the good properties
(it just needs to get some numbers from IANA to be usable :-).

   to that more local COA.

=> this is the hierarchical mobility idea: hide local movements...

   The only concern I have with putting the COA
   directly on the mobile device is the need for someone to forward them
   during handoffs, and this would allow for that. It seems like this "helper"
   model is not dissimilar to the Hierarchical Mobility model, but simpler.

=> I've seen an answer by a hierarchical mobility person...

Regards

---

From: Claude Castelluccia <[email-masked]>
Date: Tue, 17 Oct 2000 17:31:19 +0200

Hello Fred,

> another bit; we need quite a bit on the routing aspects of the technology.

As a co-author of the draft, I of course do not agree with you.
There is nothing marketing about this draft. We describe in detail
our protocol.
What do you thing is missing in this draft? We will be very happy
to make any useful additions that will make it more technical...
BTW we also have an implementation ( that can be
downloaded at http://www.inrialpes.fr/planete/)...
FYI I am not from Ericsson but from INRIA. INRIA is a public
research center. We are not selling anything and we do not care about
marketing...

> But I think there is a simpler approach that scales more nicely.

this looks very much like a marketing statement :-)

> model is not dissimilar to the Hierarchical Mobility model, but simpler.

I am not sure  I understand everthing but from what I have just read this
does not look simpler than HMIPv6.
HMIPv6 is just a simple extension to Mobile IPv6...I don't think one
can do simpler ;-)

> I can write up a draft if someone is interested to explore that.

yes, I think that would be really interesting and useful...

regards,

Claude.

--

----------------------------------------
Claude CASTELLUCCIA, INRIA Rhone-Alpes
ph:  +33 4.76.61.52.15 (fax: 52.52)
http://www.inrialpes.fr/planete/