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Re: Modified IPv6 to unmodified IPv4
We have been taking a look at impacts of double NAPT and there is an
interesting paper on P2P friendly NAPT from Bryan Ford, Pyda Srisuresh
and Dan Kegal. Take a look at section 3.5
Peers Behind Multiple Levels of NAT.
I don't think anyone is suggesting IPv4 with NAPT is a IPv6 alternative,
but more a complementary one that has become a necessity given how late we
have left things. During the transition period to IPv6 there will be a
mixture of IPv4-only, and IPv6-capable hosts - we are dealing with two
distinct issues: The exhaustion of IPv4; and, the transition to IPv6.
Implementing IPv6 in the provider network is comparitivly easy compared to
changing all the clients to support it.
Some fear that work to support continued IPv4 use will undermine the
transition to IPv6 - the industry as a whole must move forward with one
voice: IPv6 is the future, but we will not abandon IPv4 on D-day.
Addressing Peer-to-Peer, provider NAPT and NAT-PT/NAT46 should be items we
the industry take on. We can forsee these issues today, now we need to
agree whether we sholud do something about them within the IETF.
On Sat, 20 Oct 2007, Iljitsch van Beijnum wrote:
On 19-okt-2007, at 13:32, Nathan Ward wrote:
It is unclear to me why one would not just deploy traditional IPv4 NAPT and
regular IPv6 - it works with existing protocols, is significantly more
simple, and end user hardware is (we are told) being worked on.
The crucial difference is that in that case, the host must have IPv4
connectivity. Although building a NATed IPv4 network would at first seem
easier or not much more difficult than building an IPv6 network with some
gateways, I think the latter is a better way forward, especially as we're
getting closer to running out of IPv4 addresses. As soon as ISPs start NATing
their customers, many people will be behind double NAT, which makes it
impossible to open up ports to make peer-to-peer protocols work through a
single layer of NAT.
If the ISP hosts the IPv6-IPv4 gateways, then it's possible to have a clean,
routed path between the gateway and the end-user, even if a site has multiple
hosts, which pretty much requires NAT for SOHO sites for IPv4 today.
Another advantage is that the gatewayed IPv4 connectivity and real IPv6
connectivity go hand-in-hand so users always get both access to the legacy
IPv4 infrastructure and the new IPv6 infrastructure that (hopefully) allows
peer-to-peer applications and new protocols that would require an ALG with
NAT. With regular IPv4 NAT it's still an extra hurdle to get IPv6 in there so
large numbers of users will have to live with reduced transparency for some