Trace (also known as Traceroute or TRACERT in Windows) is a utility that traces a the route that IP (Internet Protocol) packets take from your computer to an internet host, showing how many hops the packet requires to reach the host and how long it takes to reach each router. If you're visiting a Web site and pages are appearing slowly, you can use traceroute to figure out where the longest delays are occurring.

The original traceroute is a UNIX utility, but nearly all platforms have something similar. Windows includes a traceroute utility called tracert. In Windows, you can run tracert by selecting Start->Run then typing "cmd" into the 'Open' field box, and then entering tracert followed by the domain name of the host. For example:

tracert www.pcwebopedia.com

Traceroute utilities work by sending sequential IP packets with incremental time-to-live (TTL) fields. The TTL value sets a maximum number of hops the packet can go through before it is rejected as an 'expired' packet. When this happens, the last router which received the packet returns a 'TTL expired' ICMP packet, which reveals the router's IP address, and by comparing the time when the packet was sent out and the time the 'TTL expired' packet came back an estimated time to reach that router can be calculated.

By sending a series of packets and incrementing the TTL value with each successive packet, traceroute finds out who virtually all the intermediary hosts are.

This facility is offered to customers through the 'Web Diagnostics' section in your Online Control Panel Control Panel.

Notes:

- The time quoted - RTT (round trip time) - is the time it took the packet to reach the router in question, plus the time it took the router to send an error message back. Since the route back might not be identical to the route to get there, this value is not necessarily equal to double the time it took the packet to reach the router.

- Don't worry if one or two of the middle hops show:

2 * * * ...or similar, as that often just indicates a router configured to not reply via ICMP.

- The main number you should be concerned with is the RTT for the last hop. Anything under 60 ms is fast, and anything under about 300ms is perfectly usable.

- Windows tracert.exe and UNIX traceroute differ in that tracert.exe sends ICMP echo packets, while traceroute sends UDP data packets, see below.

- RTT is not an indication of transfer speed or available bandwidth, although a router under bandwidth pressure is more likely to drop ICMP packets or provide very slow replies to them.