can we disable AAAA queries in the resolver ?

[Lev Walkin]

Luigi Rizzo wrote:
> hi,
> recently i have been bitten by a problem which might be already
> known, but still...
> 
> quite a few apps (sendmail and ssh among them) seem to always
> try an AAAA query if compiled with ipv6 support, and even if
> the kernel does not support ipv6, tcpdump shows AAAA queries going out
> to the nameserver, and often timing out or otherwise causing my
> apps significand delays at startup.
> 
> My understanding is that there are multiple buggy components here:
> my ISP's nameserver certainly shouldn't behave so badly on AAAA
> requests, and the applications should not bother asking AAAA queries
> when the kernel has no ipv6 support.
> On the other hand, the resolver code is probably just innocent
> because if some application issues an AAAA request, the resolver
> has no reason to object. Still, rather than fixing the many
> broken applications, or the nameserver (on which i have no control)
> i wonder if it is possible to instruct the resolver, perhaps through
> some option in resolv.conf, to immediately return some kind
> of negative replies on selected queries ?

The code does not seem to have this as an option, but it is rather
a compile-time stuff. Refer to the /usr/src/lib/libc/net/getaddrinfo.c.
Indeed, it would be useful to have it configurable either in resolv.conf
(options) or as an environment variable (RES_OPTIONS).


-- 
Lev Walkin
vlm at netli.com