RFC 6724

Phillip Hellewell sshock@gmail.com
Mon Nov 12 16:50:00 GMT 2018

On Mon, Nov 12, 2018 at 4:20 AM Florian Weimer <fweimer@redhat.com> wrote:
> RFC 3484 has always been rather problematic (particularly Rule 9, which
> we do not implement).
> I seriously doubt that there is any benefit from address sorting.  It's
> a layering violation, and it makes renumbering harder because you now
> need to consider the impact on address sorting.  Its core assumptions
> are also quite wrong on many networks (e.g., private addresses often
> have less georeplication than public Internet service, so public
> addresses are closer by).
> In any case, I think address sorting should be performed by the caching
> DNS resolver, not the stub resolver.

An administrator of a given machine may not have any control over the
DNS server, yet they should still be able to control address order,
e..g., to prefer IPv4 over IPv6 or vice-versa.

> Do you have a setup that actually relies on address sorting?  Do you
> have any examples where DNS provides a set of addresses for a single
> name with different labels/precedence, so that sorting the addresses
> actually has an effect?

Yes, this happens all the time.  Look no further than google.com.  It
has both A and AAAA.  As a system administrator, I should be able to
set up my prefix policy table to prefer IPv4 over IPv6 if desired.
That is just one example.  See RFC 6724 for more examples.

One should be able to control address order without having to set up
and run their own special DNS server/proxy/whatever.

> Currently, we have a lot of code which is questionable at best when it
> makes a difference, but it's mostly unused.  I would like to remove it,
> rather than keep maintaining it.

Please don't take away this ability.  I honestly can't believe you are
even suggesting it.  That would be three steps backwards and cripple
Linux's IPv6 support.  I would have to say Linux doesn't support IPv6
if you did that.

If you don't want to update the policy table to the latest RFC, just
leave it alone and forget I said anything.


More information about the Libc-help mailing list