Subject: MIPv6 and site local addresses

From: Thomas Narten <[email-masked]>
Date: Mon, 11 Nov 2002 12:19:19 -0500

One more apparent headache: a mobile node running mobile IP for IPv6
(MIPv6) will often be in 2 different domains simultaneously. It's home
domain (where it continues to have a Home Address and the domain that
it is currently visiting). How does one handle site-locals in this
case?

Consider the comparatively easy configuration where MIP is using
global addresses for everything, but both sites happen to use SLs for
some of their own internal stuff. When the MN needs to send an IP
packet to a particular address, and it is a SL address, where does it
send it?  should it:

- tunnel it back through the Home Agent? (I.e., assume the address is
  for a node at its home site)

- send the packet locally (i.e, assume the packet is for a node on the
  local site)

Problem is, neither answer is right in all cases, and it seems like
there are no easy rules for making the right thing happen in all
cases. This leads me to conclude that using both SLs and MIP together
will lead to scenarios where communication will fail, when the typical
user will expect them to succeed. This does not seem good like a good
situation.

Note that a fundamental assumption (at least in my mind) is that when
one uses MIPv6, everything should "just work". SLs seem to introduce
some problems here.

Note that the situation is a whole lot messier still, if the MN's Home
Address is SL, or if the HAs it is using are SL. But one can at least
say "don't do that". But it still leaves the above issue unresolved.

Thomas
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From: Charlie Perkins <[email-masked]>
Date: Mon, 11 Nov 2002 12:27:33 -0800

Hello Thomas,

> - send the packet locally (i.e, assume the packet is for a node on the

What if the rule is that the mobile node tunnels when it is away
from home, and sends the packet locally when it is deregistered
and attached to its home network?  I don't see the case where
that isn't a reasonable thing to do.

Our current restriction is that a mobile node that uses a site-local
home address also must have a site-local care-of address when
using that address.  I think this eliminates the problem entirely.

> one uses MIPv6, everything should "just work". SLs seem to introduce

So far, when we have had problems, we have made restrictions
(as just noted) so that indeed Mobile IPv6 just works.  Sometimes
the restrictions could be lifted by specifying additional protocol, but
at this point the amount of additional protocol is to be reduced,
even at the cost of some restriction.

I hope this resolves the issue.

Regards,
Charlie P.

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From: Thomas Narten <[email-masked]>
Date: Mon, 11 Nov 2002 15:34:35 -0500

> that isn't a reasonable thing to do.

The problem is that this doesn't seem to work in all cases. If the
visited site is using SL addresses, the above rule means that the MN
can't use them (for conversing with local nodes, at least not while
using its Home Address). In other words, things that work one way for
a regular node at the visited cite, won't work for the MN. That
doesn't seem like a desireable property.

> using that address.  I think this eliminates the problem entirely.

The issue I cite also occurs when neither the Home Address or COA is a
SL, so I don't understand the above comment.

> even at the cost of some restriction.

My comments were prompted by my reading of the MIPv6 spec. IMO, the SL
wording there has problems. In a few places, it says things like "if
you are visiting a network with the same site as your home, then
...". But, AFAIK, we have know of no way of determining what site a
node is connected to when it visits some arbitrary link.

Thomas

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From: Charlie Perkins <[email-masked]>
Date: Mon, 11 Nov 2002 12:57:15 -0800

Hello again Thomas,

> doesn't seem like a desireable property.

I guess the Mobile IPv6 specification is not supposed to cover
cases where the mobile node is not using Mobile IPv6.  Then,
if a mobile node wants to use visited site-local addresses for
communication within the visited site, that should be O.K.

If the mobile node IS using Mobile IPv6 with a global care-of
address, then  ...? should it use that global care-of address for
other communications (e.g., very short term) for which the
home address is not involved?

> node is connected to when it visits some arbitrary link.

That is true, and it was discussed.  The conclusion we came up with is
that a mobile node might erroneously use a visited site-local address as
a care-of address, but that its home agent would never see the Binding
Update, so the mobile node would not be able to establish communications
with its home site using the visited site-local address.

This is the same, effectively, as the case where the node is not using
Mobile IP at all.

Regards,
Charlie P.

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From: Jari Arkko <[email-masked]>
Date: Tue, 12 Nov 2002 00:34:25 +0200

> home address is not involved?

The issue was simultaneous use of site-local addresses both
at the home site and at the visited site. I think the problem
is that when we see a site local address in the stack and
expect to do, say, a TCP connect to it, we don't know where
that address came from. If it came from home-site DNS then
we should somehow get to the home site. If it came from visited
network http link, then we should use it locally. I don't
think solving the problem by picking the right source address
is quite enough. This is because we may not have enough
information to do this selection. On the other hand the problem
also appears more general than just MIPv6 specific, because
other types of tunnels have similar problems.

Jari

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From: Keith Moore <[email-masked]>
Date: Mon, 11 Nov 2002 19:37:14 -0500

> I think the problem

indeed, it's much the same problem regardless of whether you're
triyng to 'connect' via a MIPv6 tunnel, another kind of tunnel,
or some layer 7 protocol that uses IP addresses as endpoint 
identifiers.  in all of these cases the fact that SLs are ambiguous
makes them very difficult to use.

Keith