[ntp:questions] Pool returns IPv6 address to IPv4 query

Rick Jones rick.jones2 at hp.com
Tue Nov 19 22:30:28 UTC 2013

Danny Mayer <mayer at ntp.org> wrote:
> On 11/19/2013 2:47 PM, Rick Jones wrote:

> > That passing-in a literal IPv6 address is precisely where I first
> > started noticing problems with netperf.  For ages (in Internet
> > Time at least) it "just worked" even when all I had were
> > local-scope (link-scope?) IPv6 addresses configured.  Then someone
> > made a libc change and life became Quite Unpleasant (tm).

> You should not be using literal IP addresses of either flavor
> without also setting the AI_NUMERICHOST flag otherwise it tries to
> do a DNS lookup. That's poorly written code otherwise.

I guess I was spoiled by gethostbyname()?  I'll not contest whether
netperf contains poorly written code - it has plenty :) but I'll
point-out that looking at the Linux manpage for getaddrinfo() I get
the impression it is a suggestion rather than a requirement:

       node specifies either a numerical network address (for IPv4,
       numbers-and-dots notation as supported by inet_aton(3); for
       IPv6, hexadecimal string format as supported by inet_pton(3)),
       or a network hostname, whose network addresses are looked up
       and resolved.  If hints.ai_flags contains the AI_NUMERICHOST
       flag then node must be a numerical network address.  The
       AI_NUMERICHOST flag suppresses any potentially lengthy network
       host address lookups.

I parse that as "If AI_NUMEICHOST then must be addr" rather than "If
addr, must be AI_NUMERICHOST."

A: Because it fouls the order in which people normally read text.
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