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Re: IPv6 and IPv4 resolver preferences



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Felipe Alfaro Solana wrote:

> When running "telnet computer1" and looking at the packets captured by
> Ethereal, I can see _exactly_ four queries, all of them asking for the
> RR host record of "computer1.mydomain.com", that is, four queries asking
> for the same FQDN. Of the four queries, the first one asks for the AAAA
> RR, while the remaining three ask for the A RR.

Look again.  There are two and two.  And you'll have to look at the so
ruces for the old glibc version.  It's not important enough to explain
in detail here given that all these are implementation details which
have changed.


> In my case, it's just the other way around. I DO want IPv6 queries, and
> I DO want IPv6 to always have precedence over IPv4. Anyways, I'll get
> glibc-2.3.3-53 as soon as it's available.

getaddrinfo does sorting according to RFC 3484.  If the v4 addresses are
before the v6 addresses in the list returned by getaddrinfo, then the v4
addresses are deemed preferrable.  Usually this is the correct result.
There are a few cornercases of RFC 3484 which I cannot implement at
userlevel and there are a few places where the RFC 3484 is outdated (wrt
to other parts of IPv6), but I hardly think this is a real problem.

So, adjust your interfaces so that the address selection prefers the v6
addresses.  And read RFC 3484.

- --
â Ulrich Drepper â Red Hat, Inc. â 444 Castro St â Mountain View, CA â
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