CIDR FAQ

Fri Aug 18 18:43:07 UTC 1995

Kent,

> If you have an IPv6 capable host, why use "IPv4 compatible" addresses?  Why
> not use an algorithmic translation that includes a provider prefix?  It
> would seem to me that any IPv6 host should have the capability to
> algorithmically translate its IPv4 address, preferably dynamically.

IPv4 compatible addresses are needed to allow IPv6 communication across
IPv4 only "cloud". This way a router at the border between "dual"
(IPv6/IPv4) part of a network  and IPv4 only part of the network can
determine packet's destination by just looking at the low order 32 bits
of the IPv6 destination address (the IPv4 address is needed to figure
out how to tunnel the packet across the IPv4 only part of the
network).  An alternative would be to maintain a static mapping on the
router (and this is a not an easy manageable proposition).

Yakov.

P.S. Perhaps this discussion is a bit outside the scope of this list,
so we should either (a) continue this in private, or (b) move it
to the IPng mailing list.