When computers communicate over the Internet, there are often many connections made along the way. This is because the Internet is made up of a network of networks, and two different computers may be on two separate networks in different parts of the world. Therefore, if a computer is to communicate with another system on the Internet, it must send data through a series of small networks, eventually getting to the Internet backbone, and then again traveling to a smaller network where the destination computer resides.
These individual network connections, called "hops," typically go unnoticed by the average user. After all, why bother tracking all the various connections when you are only interested in communicating with the destination computer? However, if a connection cannot be made or is taking a unusually long time, tracing the path of connections along the way can prove to be helpful. This is exactly what the traceroute command does.
Traceroute is a TCP/IP utility that allows a user to trace a network connection from one location to another, recording every hop along the way. The command can be run from a Unix or DOS command line by typing tracert [domain name], where [domain name] is either the domain name or the IP address of the system you are trying to reach. A traceroute can also be done using various networking utilities, such as Apple's Network Utility for Mac OS X.
When a traceroute is run, it returns a list of network hops and displays the host name and IP address of each connection. It also returns the amount of time it took for each connection to take place (usually in milliseconds). This shows if there were any delays in establishing the connection. Therefore, if a network connection is slow or unresponsive, a traceroute can often explain why the problem exists and also show the location of the problem.