[e2e] source code release

[Christian Huitema]

There is a whole family of protocols that work by overlaying a unique
name space on top of the existing IPv4 infrastructure. These protocols
are deployed by adding software to the end stations (to understand the
new overlay convention) and also optionally in some relays, to overcome
connectivity limitations. Your proposed 4+4 experiment has exactly those
characteristics: change the hosts so they understand the convention;
change the relays so they can do some form of "cross realm" routing.
This is not radically different from other experiments, like HIP, or
indeed like the IPAE proposal of 1992. 

You can achieve exactly the same result with a combination of two
currently deployed IPv6 services, 6to4 and ISATAP; 6to4 provides an IPv6
overlay on top of the connected IPv4 backbone; ISATAP provides an IPv6
overlay on an IPv4 private realm. The requirements of the 6to4/ISATAP
combo are exactly the same as the requirement of any other overlay
solution: upgrade the participating hosts, and upgrade the enabling
"NAT". You can in fact achieve an even better result by using the Teredo
approach, which overlays IPv6 on top of UDP, and as such does not
require upgrading most NAT.

Using IPv6 to structure the overlay has the big advantage of a clean
exit strategy: as some point, we can quit overlaying, and just route
IPv6.

-- Christian Huitema