Subject: RE: draft-ipngwg-default-addr-select-00.txt

From: Tim Hartrick <[email-masked]>
Date: Tue, 26 Oct 1999 09:51:30 -0700 (PDT)

Richard,

> 
> So you can't assign global addresses to your tunnel interfaces?
> Ignoring the "fix your implementation" response...
>

Hmm...  This is a bit pejorative.  The implementation does not require
fixing.  It works as intended.

I freely admit that in order to support routing protocols over tunnels,
implement 6to4 or 6over4 the implementation of tunnel interfaces needs
to be more expansive.

However, to support automatic tunneling and support configured tunnels
modeled as routing table entries the implementation is adequate to the
task.

I didn't intend to have to defend our implementation.  I was merely
attempting to echo KRE's feelings about the utility of something like IPv4
unnumbered interfaces.

> One thought is that an interface that can't be assigned addresses shouldn't
> qualify as an interface. So from this perspective, your node would just have
> the ethernet interface plus a routing table entry referring to an
> implementation structure that has some passing similarity to an interface.
> Then the global address would be available as a source address when sending
> to the 6bone.
>

It has been assigned an address.  That address is an IPv4 compatible IPv6
address.  That assignment happens automatically, but it happens.
 
> Another thought: how will your node receive packets from the 6bone that are
> sent to the global address? They will be arriving via the tunnel. So it
> would seem that your implementation uses a "weak host" model? In Oslo and
> Tokyo the working group was considering a "semi-strong" model for IPv6 that
> I think would rule out your implementation (at least if the tunnel is
> considered to be an interface).
>

Both interfaces are configured to forward datagrams.  Since I haven't read
a definition of what the "semi-strong" model is I can't comment on it.

> A final thought, appropriate only for routers: you could consider the
> ethernet interface to be originating/receiving packets using the global
> address, and it's internally forwarding the packets over to the tunnel
> interface. If this is a desired viewpoint, I'd want to change the draft to
> be more explicit about effectively enlarging the candidate set of source
> addresses on routers.
> 

Yes, that is in essence what is happening.  I think the language would need to
be tightened (loosened?) to take into account the IPv6 equivalent of unnumbered
interfaces.  That assumes of course that we determine that a facility like
unnumbered interfaces still has utility in the IPv6 world.

The reason these things have been used in the IPv4 world was to avoid burning
down lots of address space at the server end of PPP dialup connections.  That
is less of a concern for IPv6 however they also have the added benefit of
making PPP dialup boxes at least a little easier to administer.

Tim Hartrick
Mentat Inc.
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