CIDR FAQ

David,

> But isn't it possible to have a router convert from an IPv6 address
> with provider bits to an IPv4 address by simply stripping all but the
> lowest 32 bits from the IPv6 address?
> 
> The hosts on the LAN remain entirely IPv4, but the addresses that
> leave the router have the provider bits added by the router.

You can't strip a non-zero part of IPv6 address, as this would cause
transport layer pseudo-header checksum to fail.

Yakov.