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

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

SungJin Lee <[email-masked]> writes:
> What is the difference between two advertisement below ?
>       - Renumbered home link router advertisement
>       - 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

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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:
>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?

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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.

At 09:37 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 ?
>
>         with stateless autoconfiguration. At a time the router changed 
> the home link
>         received ? isn't it possible the IPv6 node to think it's moved to 
> a foreign
>         link and start MIPv6 process ?
>
>

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From: "Vanitha Neelamegam" <[email-masked]>
Date: Mon, 16 Oct 2000 19:29:41 +0530

Hi,
	Can anyone suggest me a IPV6 router (something like IPV4 Gated, which runs
in Linux Environment) which can be used for interop testing.

regards,
Vanitha

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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.
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