Re: [DNSOP] Why would a v4 client send AAAA query?

[Mukund Sivaraman <[e-mail]>]

On Thu, Aug 29, 2019 at 03:13:45PM +0530, Naveen Kottapalli wrote:
> My query was about the behavior we observed on a gateway where a pure v4
> subscriber (not dual-stack) has sent both A and AAAA query for the same
> domain simultaneously.  Just wanted to know why would a pure v4 subscriber
> which cannot use the resolved AAAA domain addresses is trying to resolve
> the v6 addresses of the domain.

As Viktor pointed out, when a process calls getaddrinfo() without hints,
some libc implementations of getaddrinfo() don't consider what address
families the system has configured as it doesn't matter at that library
interface.

For example, here is FreeBSD's getaddrinfo() implementation:

https://github.com/freebsd/freebsd/blob/master/lib/libc/net/getaddrinfo.c#L2301

So, for example, FreeBSD's ping which uses gethostbyname2() with AF_INET
will appear to lookup only the A record of a hostname being pinged,
whereas FreeBSD's telnet which uses getaddrinfo() without hints (which
gets converted internally to AF_UNSPEC) will appear to lookup both A and
AAAA records.

Also what Mark said applies that even if you think a subscriber has no
v6 address/stack, they probably do.

		Mukund