icmp 3/5 message makes the most sense

[Francis Dupont]

> but it really seems to me this needs to be an icmp6 message, originating from
> 2001:db8:0:1::1, going to the cpe  which is at (at the moment) :2 or :3

=> no! And it is not a DS-Lite feature so it has nothing to do with IPv6.

> not an icmp4 message, which has no real internal destination

=> its destination is the source of the message (BTW this means it can
be natted back).
One important characteristic is the source address must be the shared address.

Regards

Francis Dupont <fdupont at isc.org>