Hector Santos <hsantos(_at_)santronics(_dot_)com> writes:
IPv4 and IPv6 are very different and software NEEDS to change in order
to even BEGIN to thinking about supporting it.
I have to pick this nit. The difficulty of supporting IPv6 in userspace
programs tends to be exaggerated. At least on UNIX varients, programs
that use the new getaddrinfo and getnameinfo interfaces can frequently be
written to be entirely agnostic about which IP stacks they're using.
I agree that changes are required for older software written against the
gethostbyname and related interfaces and for many things that one wants to
do in servers, not to mention weird network programs like ping or
traceroute require more work. But for many common typical client
networking patterns, nothing other than writing to the new generic name
and address resolution interfaces is required.
I've written code that works fine with IPv6 without even testing on an
IPv6-enabled system. The code from my perspective as a programmer is
identical either way.
In fact, from that perspective, it would be a bit annoying to write a
fallback to A without also writing a fallback to AAAA for hosts without an
MX record. The obvious (at least with thirty seconds of thought, and I
may be missing gotchas) way of implementing resolution of a mail server is
to do an MX record lookup and, if that fails, call getaddrinfo on the RHS
and connect to the resulting addresses until one of them works. This
would treat AAAA identically to A.
--
Russ Allbery (rra(_at_)stanford(_dot_)edu)
<http://www.eyrie.org/~eagle/>