Traceroute is a command-line based tool used to identify the path used by a packet to reach its destination. This tool uses ICMP message, but unlike ping, it identify every router in a path taken by the packet. Traceroute is useful when troubleshooting network problem because it can help identify where exactly the problem?. You figure out which router in the path to an unreachable target should be examined more closely as the probable cause of the network’s failures.
Traceroute send a series of ICMP echo request packet to the destination. First series of messages has Time to Live (TTL) parameters set to 1, which means the first router in a path will discard the packet and send an ICMP Time Exceed message. TTL is then increased by one until the destination host is reach and an ICMP echo reply message is receive. Originating host can use received ICMP message to identify all routers in a path.
Traceroute command on Windows named tracert. On Unix and Cisco IOS traceroute it is invoke using the traceroute command.
Below is an example of using the tracert command in Windows:
In the above output you can see the traceroute command has list the IP addresses of all the routers in the path.
Traceroute on Unix-like operating systems
Traceroute command on Unix work slightly different than Windows. It use UDP packets with large destination port numbers (33434 to 33534) that is unlikely to be use by any applications at the destination hosts. Like the Windows command, traceroute on Unix use TTL to get the IP addresses of the intermediary router. When a destination host is reached, it replies with an ICMP port unreachable messages.
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