wayne at schlitt
Nov 27, 2006, 5:29 PM
Post #18 of 33
In <200611272347.kARNlEqG047492 [at] asarian-host> Mark <admin [at] asarian-host> writes:
Re: IP4 mapped IP6 connection controversy
[In reply to]
> Purely from a sender perspective, is not the sole purpose of publishing an
> ip6 mechanism to indicate that it should only have meaning/relevance on an
> IPv6 socket?
I think that is what is being debated.
> ... Even if the SMTP connection is
> via IPv6, an IPv4-mapped IPv6 IP address (see [RFC3513], Section
> 2.5.5) MUST still be considered an IPv4 address.
> All fine and dandy. But again, what is the relevance of "seeing" an IPv4
> address on an IPv6 connection? The socket-type, IPv4 or IPv6, should
> determine which of the namesake mechs has (mutual exclusive) relevance. So
> as to say that "v=spf1 ip6:::FFFF:220.127.116.11 -all", while, according to
> our RFC, MUST still be considered an IPv4 address, STILL should have no
> relevance as IPv4 address in the context of evaluating an ip6 mech on an
> IPv6 connection. As if saying: "You have the right key, but you're trying
> to open the wrong door with it."
Ok, I'm far from an IPv6 expert, but my understanding is as follows:
Besides the case that Julian mentioned, where an OS may translate all
sockets, whether they are IPv4 or IPv6, into IPv6 sockets so that
applications just have to deal with one format, there are other cases.
It is quite possible to have a host that has IPv6 connectivity only,
just like it is possible to have only IPv4 connectivity. Such an IPv6
host will, for the next few decades, almost certainly need to use an
IPv4 gateway to access IPv4-only hosts. Such a gateway will act very
much like NAT gateways and the RFC1918 private addresses, such as the
10.x.y.z space. This includes having things similar to
port-forwarding where a connection on a certain IPv4 address on port
80 will get translated by the IPv6<->IPv4 gateway into a connection on
the IPv6-only host on port 80.
So, some IPv4-only machine goes off and tries to send mail to
ipv6-only.net. It will connect on some "IPv4" address and use port
80, which will automatically get run through the gateway.
ipv6-only.net will now see an IPv6 socket connection using an
IPv4-mapped IPv6 address.
Another case is that even if a host has both IPv4 and IPv6
connectivity, it may be the case that the fastest/best routing is to
use a IPv4<->IPv6 gateway and end up in a similar situation as above.
While this is almost never the case today, that could easily change in
another 10 years.
Corrections and/or questions are welcome. As I said, I'm not an IPv6
expert and I may misunderstand this and I certainly could be doing a
poor job of explaining it.
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