As a versatile network monitoring tool, Nagios can monitor the health of various network elements such as routers and switches. Among others, Nagios can be configured to monitor BGP sessions of a router, and generate alerts whenever there is something wrong in existing BGP session(s). Several BGP monitoring plugin tools exist for Nagios. These tools are useful in monitoring critical BGP peers of a router, and generating alerts for them. This tutorial will explain how to monitor BGP neighbors using Nagios plugin tools.