Essential NetTools Help Documentation

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TraceRoute is a tool that traces the route (the specific gateway computers at each hop) from a client machine to the remote host being contacted by reporting all the router IP addresses in between. It also calculates and displays the amount of time each hop took. TraceRoute is a handy tool for both understanding where problems exist in the Internet network and for getting a detailed sense of the Internet itself.

TraceRoute works by causing each router along a network path to return an Internet Control Message Protocol (ICMP) error message. An IP packet contains a Time-To-Live (TTL) value, which specifies how long it can go on its search for a destination before being discarded. Each time a packet passes through a router, its TTL value is decremented by one; when it reaches zero, the packet is dropped, and an ICMP TTL expired in transit error message is returned to the sender.

The TraceRoute program sends its first group of packets with a TTL value of one. The first router along the path will therefore discard the packet (its TTL is decremented to zero) and return the TTL expired in transit error. Thus, we have found the first router on the path. Packets can then be sent with a TTL of two, and then three, and so on, causing each router along the path to return an error, identifying it to us. Some routers silently drop packets with expired TTL; for such hops you will get the Request timed out error. Eventually, either the final destination is reached, or the maximum value is reached, and the TraceRoute ends. At the final destination, TraceRoute sends an ICMP Echo Request packet (ping), and if the destination computer is reachable, TraceRoute displays Echo reply in the Response Message column.


To use this tool, enter an IP address or hostname and click Start. The following options are available:

· Start hop – allows you to set the hop from which to start tracing. It is often useful to set a value higher than 1 if the first several hops of the route are always the same; by setting a higher value you can save some time.
· End hop – allows you to limit the number of hops to trace.
· Pkt. size – sets the size (in bytes) of the data portion of the ICMP packet.
· Timeout – sets the maximum time (in seconds) TraceRoute will wait for the response from a router.
· DNS resolving – check this box if you want TraceRoute to resolve IP addresses to hostnames.
· Don't fragment – sets the Don't fragment flag in the packet.

Right-clicking on the window brings up a menu with the following commands:

· Send To – sends the selected IP address to other tools or to SmartWhois.
· Copy Results – copies the TraceRoute table to the clipboard.
· Save – saves the TraceRoute table to a file.