When you monitor an IPv6 DNS server with check_dig -6, and uses the server name (not its IP address), check_dig falls back to IPv4 if the name server does not reply immediately in IPv6. It is not the behavior I expect (if I say -6, it is because I want to be sure IPv6 works). Reading the source, it seems check_dig puts the -6 as the end of the command line (call to xasprintf ). Testing with dig on the command line, it seems indeed that -6 does not have the same semantics when used at the begin or at the end of the command line (before or after the server name). I therefore suggest this patch: <pre><code>--- ./plugins/check_dig.c.orig 2014-01-27 14:55:56.000000000 +0100 +++ ./plugins/check_dig.c 2014-01-27 15:10:07.000000000 +0100 @@ -88,8 +88,8 @@ usage_va(_("Could not parse arguments")); /* get the command to run */ - xasprintf (&command_line, "%s @%s -p %d %s -t %s %s %s", - PATH_TO_DIG, dns_server, server_port, query_address, record_type, dig_args, query_transport); + xasprintf (&command_line, "%s %s @%s -p %d %s -t %s %s", + PATH_TO_DIG, query_transport, dns_server, server_port, query_address, record_type, dig_args); alarm (timeout_interval); gettimeofday (&tv, NULL); ̀`̀` Yes, dig's parsing is... special. </code></pre> — Reply to this email directly or <a href='https://github.com/monitoring-plugins/monitoring-plugins/issues/1228'>view it on GitHub</a>.<img src='https://github.com/notifications/beacon/5514713__eyJzY29wZSI6Ik5ld3NpZXM6QmVhY29uIiwiZXhwaXJlcyI6MTcwNjM2NDczMCwiZGF0YSI6eyJpZCI6MjQzMjI3MjB9fQ==--8f5fe93e9f106eaee4eb8660a47a51f7be84091d.gif' height='1' width='1'>