Subject: RE: ISATAP in unmanaged networks?

From: "Christian Huitema" <[email-masked]>
Date: Thu, 13 Nov 2003 07:40:26 -0800

On Thu, 13 Nov 2003, Fred Templin wrote:
> I have not studied this space, but it occurs to me that ISATAP
> could be tried as a first alternative to check whether the two
> hosts are separated by a NAT. If there is no intervening NAT,
> it seems to me that ISATAP would provide the benefit of not
> needing the UDP header and "bubble" packets, yielding
> greater efficiency. Otherwise, if blocked by a NAT the
> initiating host coud after a short timeout try again with
> Teredo.

Pekka already answered: we considered ISATAP, and found only one domain
of applicability, the "corner case" that Pekka mentioned. If the ISP is
not providing global addresses (e.g. provides net 10 addresses to
subscribers), then the subscribers cannot use the 6to4 technology. The
nodes could use Teredo, but the current specification requires that the
Teredo server uses a global address, which means that the Teredo clients
will have good connectivity with nodes outside the ISP, but poor
connectivity with nodes on the inside. Subscribers of a net 10 ISP will
be better served if this ISP provides an ISATAP service, including a
router. This will enable direct connectivity between the nodes, and
communication through the ISATAP router with the nodes outside the ISP.
We will document that.

However, the service only provides one IPv6 address per IPv4 address.
When the unmanaged network is connected through a NAT to a net 10
network, the nodes behind the NAT cannot directly use an ISATAP service
provided by an ISP. 

-- Christian Huitema 

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