I'm currently running a single Nagios instance. From time to time, I'm getting false alarms about timeouts - for example, it says that HTTP is down on some server, but when I open it in my browser several seconds later, it loads fast, and in general there is no trace of an error.

What can I do to reduce such false alarms?

I'm guessing that it's because of transient network issues on my monitoring server. I guess that setting up another monitoring server on a different network would greatly help, but how do I plug it into Nagios?

Is it at all possible with Nagios or do I have to switch to another monitoring system? I like my configs and, if possible, I'd like to stay with Nagios or something compatible (Icinga?)