Traceroute is a utility that records the route (the specific gateway computers at each hop) through the Internet between your computer and a specified destination computer. It also calculates and displays the amount of time each hop took. Traceroute is a handy tool both for understanding where problems are in the Internet network and for getting a detailed sense of the Internet itself. Another utility, PING, is often used prior to using traceroute to see whether a host is present on the network.
</> The traceroute utility comes included with a number of operating systems, including Windows and UNIX-based operating systems (such as IBM's AIX/6000) or as part of a TCP/IP package. If your system doesn't include the utility, you can install it. There are freeware versions that you can download.
When you enter the traceroute command, the utility initiates the sending of a packet (using the Internet Control Message Protocol or ICMP), including in the packet a time limit value (known as the "time to live" (TTL) that is designed to be exceeded by the first router that receives it, which will return a Time Exceeded message. This enables traceroute to determine the time required for the hop to the first router. Increasing the time limit value, it resends the packet so that it will reach the second router in the path to the destination, which returns another Time Exceeded message, and so forth. Traceroute determines when the packet has reached the destination by including a port number that is outside the normal range. When it's received, a Port Unreachable message is returned, enabling traceroute to measure the time length of the final hop. As the tracerouting progresses, the records are displayed for you hop by hop. Actually, each hop is measured three times. (If you see an asterisk (*), this indicates a hop that exceeded some limit.) If you have a Windows operating system, try traceroute out by clicking on Start-->Programs-->MS-DOS Prompt, and then at the C:WINDOWS prompt (or run cmd as administrator), enter:
tracert www.google.com
or whatever domain name for a destination host computer you want to enter. You can also enter the equivalent numeric form of the IP address.
Source from: whatis.com
