traceroute is a network diagnostic tool for IP networks. Like many simple network utilities, it is available on multiple platforms and under Windows as tracert. Its purpose is to display the path of packets and the transit delays in each step. A step is referred to as a hop. The RTT of each hop is recorded; the sum of the mean times in each hop is a measure of the total time needed to establish a connection. By default, it outputs the result of each hop and the final results. It sends out three packets and proceeds unless all three packets are lost more than twice. If this happens, the connection will be considered lost; therefore, the route/path cannot be evaluated. By default, traceroute uses UDP.

traceroute is available at the Windows command prompt as tracert, but unfortunately, it is not part of most default Linux installations. However, it is available from the repositories. You can obtain it from a standalone package (traceroute); you can also obtain it as part of the inetutils-traceroute utilities.

The output of traceroute is simple: the first column displays the hop count, and the last column displays the IP address and hostname. The middle three columns display the RTT of each of the three packets sent. The only required parameter for this utility is the hostname or IP address of the destination host.

You can also invoke traceroute from the pfSense web GUI, which you can do by navigating to Diagnostics | Traceroute. You can enter the hostname or IP address in the Hostname field, and you can select the protocol in the IP Protocol drop-down box. The source address of the trace can be set in the Source Address drop-down box. You can also set the maximum number of hops and enable DNS lookup. You can even change the protocol used by traceroute from UDP to ICMP. When you are done configuring the session, you can click on the Traceroute button.