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Re: I-D Action:draft-van-beijnum-modified-nat-pt-02.txt
On 3 dec 2007, at 14:39, Brian Dickson wrote:
Do IPv4-to-IPv6 protocol translation - but now, the extra "twist" -
embed the *port* in the IPv6 destination, *above* the IPv4 address.
This lets us set up "generic" ALGs, based on covering aggregates for
the "special" address space we use for the place where 6-back-to-4
happens.
And, we can then set up ALGs on a per-port basis, which are more-
specific addresses.
When I read this it wasn't obvious to me what you meant, but being
able to talk in person can sometimes be helpful. :-)
The idea is to have a format like ::port:v4:addr which makes it
possible to route all traffic for a given destination port to a
separate translator that is better prepared to translate the protocol
in question. This is a good trick!
There are even a few advanced tricks that can be accomplished, like
reverse-port-mapping to request inbound port(s) and possibly inbound
port+IPv4 address "reservation".
Combined with dynamic DNS, it may be possible to extend the
usefulness of a very small number of IPv4 addresses, to support a
much larger of "servers" who need reserved ports, although possibly
only intermittently. (Think SMTP for hosting, inbound with MX and
relay.)
Right, there are services that need a more or less permanent inbound
capability and others that only need this at certain times. I'd say
that SMTP is an example of the former, though. The latter would be
things like peer-to-peer applications that only run once in a while,
such as videoconferencing.
The implementation of things like DHCP (for IPv4) use well-know IPv4
"broadcast" address destination 255.255.255.255. But, having an IPv6
host listen on that address, transmogrified by the mapping including
port, means a specific IPv6 address can act as a DHCP server (or
relay).
Is this useful?
Oh, yeah, one other good thing - there is no requirement that the
ALGs or NAT-PT exist on the same network, just that they be
reachable via IPv6 natively. So, a small network could point their
"ALG default" at an upstream, who then would handle all the NAT-PT
stuff (presumably as either a value-add, paid, or bundled service)
for access to the V4 Internet.
Indeed.