Standard Nagios Plugins 1.4.9 and IPv6 problem?

[Frost, Mark {PBG}]

Hello.  We've been noticing that our Nagios host (Red Hat ES 3 release
3) has been sending out quite a lot of IPv6 DNS requests (I guess those
are "AAAA" record requests on port 53).  As our box is not configured to
do IPv6, this was a puzzlement.  At first I assumed it was some weird
resolver library configuration issue, but we couldn't find anything.

We started running funky queries (ones we new Nagios wouldn't normally
run) and looking for them via tcpdump on port 53.  We found that if we
ran pretty much any off the nagios-plugins package, it would generate
these IPv6 packets.  I did not enable IPv6 when I built the package.  I
tried rebuilding everything explicitly saying "--without-ipv6".  It made
no difference.

It appears that some of the check_ programs (like check_http,
check_ldap, check_tcp, check_smtp) have #ifdefs for IPv6 and allow the
command to take a -4 or -6 argument presumably to force IPv6 or IPv4.  I
tried that on a few tests and a '-4' did seem to suppress the IPv6 DNS
requests.  However, it appears that some commands like 'check_nt' which
we use rather heavily do not support the -4 flag and will generate the
extra 4-6 DNS IPv6 queries every time.  Based on the amount of traffic
we're doing on this box, this extra traffic is proving to be rather
painful.

I then ran the same test using our check_nrpe and it does not generate
IPv6 packets.  This leads me to believe there's something about the
nagios-plugins package that perhaps has some common code that
inadvertently generates all these IPv6 DNS queries.  For us, it
generates 4-6 extra queries as IPv6, fails, then falls back and does a
single IPv4 query which works immediately.

I went over to a test box we have running OpenSuse 10 and it's doing the
same thing.  This leads me to believe that is not the OS or resolver
configuration, but it's something to do with the standard plugins
themselves.

>From a quick glance at the code, it appears that if it detects that IPv6
is available on the box (even if it's not configured to use it), it's
going to try to query it.

Has anyone else seen this behavior?

Mark

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