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Traceroute is a network diagnostic tool used to track the pathway taken by a packet on an IP network from source to destination. Traceroute also records the time taken for each hop the packet makes during its route to the destination.
Traceroute uses Internet Control Message Protocol (ICMP) echo packets with variable time to live (TTL) values. The response time of each hop is calculated. To guarantee accuracy, each hop is queried multiple times (usually three times) to better measure the response of that particular hop.
Traceroute exists as part of most operating systems in one form or another.
A traceroute is also known as a tracert.
Traceroute is a very useful tool for determining the response delays and routing loops present in a network pathway across packet switched nodes. It also helps to locate any points of failure encountered while en route to a certain destination.
Traceroute uses ICMP messages and TTL fields in the IP header for its operations, and transmits packets with small TTL values. Every hop that handles the packet subtracts "1" from the packet's TTL. If the TTL reaches zero, the packet has expired and is discarded. Traceroute depends on the common router practice of sending an ICMP time-exceeded message back to the sender when the TTL expires.
By using small TTL values that quickly expire, traceroute forces routers along a packet's normal delivery path to generate these ICMP messages. These messages also identify the router. A TTL value of "1" should produce a message from the first router; a TTL value of "2" generates a message from the second one, and so on.
Traceroute uses the following command syntax, with or without optional parameters: tracert [-d] [-h maximum_hops] [-j host-list] [-w timeout] target_name
Traceroute output first displays the IP address of the destination and the maximum number of hops it will traverse before it will quit the trace. Next, it displays the name, IP address and response time taken at each hop.
This trace continues to the destination domain, listing all the hops along the way. It is worth noting that the trace may display different results if subsequent traces are run for the same destination. This may indicate a change of network path due to the failure of some link or hop. If a hop does not respond (request timed out), an asterisk (*) is displayed and then another hop is tried. If successful, the response time of the hop is displayed. At last, the destination domain with its IP address is displayed.