Converting between IPv4 and IPv6

[Darren Reed <darrenr%netbsd.org@localhost>]

Something that I'm looking at now with IPFilter is converting IPv4 headers
into IPv6 headers and back again as part of its NAT functionality.  One of
the big problems that needs to be solved is that packets coming in or going
out change protocol type in mid stream.  This is not something that will be
pleasant for the rest of the kernel if left alone.

So I'm thinking through how to get the IPv4 packet that came in on fxp0
and has been converted to IPv6 in the middle of ip_input() over to 
ip6_input().

I suspect that the only thing that I can do is put it on ip6intrq and 
schedule
a soft interrupt for IPv6 and have it come up through IPv6 that way.

There is also a similar issue for output.

Does anyone else have any thoughts on this?

Darren