Troubleshoot network problems with tracerout/tracert

You're probably familiar with using the ping command to see if you can access a particular node on the network. This is useful in ruling out the cause of your network problem. For example, you might initially think the Cisco router is at fault, but the machine you're trying to access may not even be turned on. However, ping only tells you a few things: Whether you can access the machine, its current IP address (if you know the computer name but not the IP), and if connections are slow (if the ping takes an unusually long time to come back).

The Linux traceroute command gives you much more information regarding what actually happens on the way between your terminal and the device you're trying to access.

But on Microsoft Windows, the correct command is tracert. If you try traceroute or trace, you're liable to get a message like "'traceroute' is not recognized as an internal or external command, operable program or batch file."

Note also that the output takes a bit longer than ping, so it may look as if it's hung for awhile, especially if there is a timeout somewhere.

Now that you know the basics of how to call this command from Linux or Windows, the next thing you'll need to learn is how to interpret its results. Tracerout (or tracert) sends three packets of information that tell you the roundrip time (in milliseconds) that it took for the packet to get to your router, the remote computer's router, and (finally), the remote computer. Thus, each row of output will show three numbers indicating the respective time in milliseconds:

    1    <1 ms    <1 ms    <1 ms server.mycompany.com [10.94.160.10]

If there are several gateways to the fínal network destination, you'll see multiple lines of output, each of which is called a "hop."

If a packet is not received back, it is shown as an asterisk. For example, this is how a timeout would look:

   1    *       *       *    Request timed out.

In some cases, you may be able to ping a machine but not effectively communicate with it. A line of asterisks from tracert may help point you to the reason for the problem.

However, don't be too concerned if you see an asterisk for the first or second column. Sometimes the machines may be configured not to return those packets.