Strange issues with DNS check

[nmail_uk]

I have a DNS check which executes every 5 minutes and checks that the server can resolve it's own IP address to its hostname.

However for one server in particular every now and then it just decides to return UNKNOWN (which then triggers an event) with nothing in the "last 500 values" for the period.

On another server it's just stopped sending results for the last 4 days with no events raised whatsoever.

All other checks on both servers are working perfectly. The same DNS check on 3 other servers is working perfectly.

The DNS check is defined in a template so there are no differences between how it's configured between servers. The command itself is: net.tcp.dns.query[{IPADDRESS}, {HOST.DNS}, A]. All my checks are active, all agents have passive mode disabled. ZABBIX is version 1.8.1 with all agents being 1.8.1.

So my questions are: why does one server send an UNKNOWN result? Surely if the DNS resolution fails, it would return PROBLEM? Why is this particular check not sending results on the other server when all other checks are working fine?

Thanks,
Andy

[nmail_uk]

OK it gets stranger: the server which is not sending results any more has the following in its log file:

10805:20100219:050537.672 Active check [net.tcp.dns.query[77.245.76.138, canberra.networkmail.eu, A]] is not supported. Disabled.

There is an entry at 5:00 and 5:05 this morning, however the last result ZABBIX received was at 19:35 on the 15th Feb (4 days ago.)

Interestingly the network to this server was a bit flaky between 4:50 and 5:20 this morning, but that doesn't explain why the check is suddenly unsupported because of this. It also doesn't explain why it's not received any results between then and the 15th Feb.

Also the status for this check is still listed as Active in ZABBIX, not inactive or not supported.

Note: I've restarted the agent on the server in question, and it's still not sending the results. This time there's nothing in the log file to indicate the check is unsupported.

[nmail_uk]

All sorted - schoolboy error!

I'd not read the parameter descriptions for the net.tcp.dns command - the first parameter is the DNS server's IP address, not the server's own IP address!

I've changed this and it appears to be working fine now.

It's bizarre that only two out of 5 servers had a problem with it though, and had still managed to receive some results - two servers of which are identical, and all running the same OS. Madness.