The Network Layer
Using the test mapped to this layer, administrators can figure out the uptime of the target router and in the process identify when exactly the router was restarted. In addition, administrators can also easily assess the quality of network connections to and from the router, and the overall health, speed, and bandwidth usage of the network interfaces supported by the router.
Figure 1 : The test mapped to the Network layer
To know how to configure the tests mapped to this layer, refer to the Monitoring Cisco Router document and Monitoring Unix and Windows Servers document.