Network Administration: The tracert Command

The tracert command (spelled traceroute in Unix/Linux implementations) is one of the key diagnostic tools for TCP/IP. It displays a list of all the routers that a packet must go through to get from the computer where tracert is run to any other computer on the Internet. Each one of these routers is called a hop, presumably because the original designers of the IP protocol played a lot of hopscotch when they were young. If you can’t connect to another computer, you can use tracert to find out exactly where the problem is occurring.

tracert makes three attempts to contact the router at each hop and displays the response time for each of these attempts. Then, it displays the DNS name of the router (if available) and the router’s IP address.

To use tracert, type the tracert command followed by the host name of the computer to which you want to trace the route. For example, suppose that you’re having trouble sending mail to a recipient at wiley.com. You’ve used nslookup to determine that the mail server for wiley.com is xmail.wiley.com, so now you can use tracert to trace the routers along the path from your computer to xmail.wiley.com:

C:>tracert xmail.wiley.com
Tracing route to xmail.wiley.com [208.215.179.78]
over a maximum of 30 hops:
  1    27 ms    14 ms    10 ms  10.242.144.1
  2    11 ms    43 ms    10 ms  bar01-p5-0-0.frsnhe4.ca.attbb.net [24.130.64.125]
  3     9 ms    14 ms    12 ms  bar01-p4-0-0.frsnhe1.ca.attbb.net [24.130.0.5]
  4    25 ms    30 ms    29 ms  bic01-p6-0.elsgrdc1.ca.attbb.net [24.130.0.49]
  5    25 ms    29 ms    43 ms  bic02-d4-0.elsgrdc1.ca.attbb.net [24.130.0.162]
  6    21 ms    19 ms    20 ms  bar01-p2-0.lsanhe4.ca.attbb.net [24.130.0.197]
  7    37 ms    38 ms    19 ms  bic01-p2-0.lsanhe3.ca.attbb.net [24.130.0.193]
  8    20 ms    22 ms    21 ms  12.119.9.5
  9    21 ms    21 ms    22 ms  tbr2-p012702.la2ca.ip.att.net [12.123.199.241]
 10    71 ms   101 ms    62 ms  tbr2-p013801.sl9mo.ip.att.net [12.122.10.13]
 11    68 ms    77 ms    71 ms  tbr1-p012401.sl9mo.ip.att.net [12.122.9.141]
 12    79 ms    81 ms    83 ms  tbr1-cl4.wswdc.ip.att.net [12.122.10.29]
 13    83 ms   107 ms   103 ms  tbr1-p012201.n54ny.ip.att.net [12.122.10.17]
 14   106 ms    85 ms   105 ms  gbr6-p30.n54ny.ip.att.net [12.122.11.14]
 15   104 ms    96 ms    88 ms  gar3-p370.n54ny.ip.att.net [12.123.1.189]
 16    98 ms    86 ms    83 ms  12.125.50.162
 17    85 ms    90 ms    87 ms  xmail.wiley.com [208.215.179.78]
Trace complete. 

The most likely problem that you’ll encounter when you use tracert is a timeout during one of the hops. Timeouts are indicated by asterisks where you’d expect to see a time. For example, the following tracert output shows the fourth hop timing out on all three attempts:

C:>tracert xmail.wiley.com
Tracing route to xmail.wiley.com [208.215.179.78]
over a maximum of 30 hops:
  1    27 ms    14 ms    10 ms  10.242.144.1
  2    11 ms    43 ms    10 ms  bar01-p5-0-0.frsnhe4.ca.attbb.net [24.130.64.125]
  3     9 ms    14 ms    12 ms  bar01-p4-0-0.frsnhe1.ca.attbb.net [24.130.0.5]
  4     *        *        *     Request timed out.

Sometimes, timeouts are caused by temporary problems, so you should try the tracert again to see if the problem persists. If you keep getting timeouts at the same router, the router could be having a genuine problem.