SNMP is sometimes feared for being not-so-simple monitoring protocol, but as a standard it has proven its worth many times and is the main way to monitor network equipment as well as supported by all operating systems. I will first discuss SNMP protocol, its data structures and its security features. Then we will discuss how to use Nagios with existing SNMP plugins and how to write new SNMP plugins in Perl while optimizing SNMP requests to minimize check completion time. This presentation is aimed for those using Nagios in Linux or other Unix environment and where standard Net-SNMP tolls and libraries are available.