[zadikian]

Owning 192.0.2.4 in v4 didn't really give you 2002:192.0.2.4 in v6, as in v6 packets can't reach you that way. If someone sent a v6 packet there, some router on their side would intercept it and relay as v4. Aside from this still relying on v4, it was very unreliable in practice because of uncertainty around what v6 route is taken to the relay. There's an RFC somewhere that looked at this in hindsight.

[throw0101a]

AIUI, you encapsulate anything to 2002:192.0.2.4/48 into an IPv4 packet with "41" in the protocol field (as opposed to 6 (TCP) or 17 (UDP)) and send it to 192.0.2.4. 192.0.2.4 would then work as the relay and extract the IPv6 traffic and handle it.

* https://en.wikipedia.org/wiki/IPv4#Protocol

* https://simple.wikipedia.org/wiki/Protocol_41