Karl Auer wrote:
host <-> home UPnP NAT <-> Carrier UPnP NAT <-> Internet <-> Carrier UPnP NAT <-> home UPnP NAT <-> host
"Trivially"? I think this looks much nicer:
host <-> Internet <-> host
Yes, if only the Internet were uniform. However, compared to V6 incapable V6 capable host <-> Internet<-> home router <-> Internet <-> 6/4 tunnel V6 capable 6/4 tunnel V6 capable end point <-> Internet <-> end point <-> Internet <-> V6 incapable home router <-> Internet <-> host which can often be: V6 incapable V6 capable host <-> Internet<-> home router <-> Internet <-> 6/4 tunnel V6 *INCAPABLE* 6/4 tunnel V6 capable end point <-> Internet <-> end point <-> Internet <-> V6 incapable home router <-> Internet <-> host
host <-> home UPnP NAT <-> Carrier UPnP NAT <-> Internet <-> Carrier UPnP NAT <-> home UPnP NAT <-> host
is just trivial and uniform.
The way it used to be before NAT, and the way, with IPv6, it can be again.
With IPv6, see above. Masataka Ohta