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Traceroute is a command-line utility that maps the path data packets take from a source to a destination by identifying each "hop" (router or switch) along the way. It works by sending packets with incrementally increasing Time to Live (TTL) values, and each router that a packet passes through decrements the TTL. When TTL reaches zero, the router sends back an ICMP "Time Exceeded" message, allowing traceroute to log the round-trip time for that specific hop. This process is repeated until the packet reaches its final destination, and the tool can be used to diagnose network performance issues by identifying where delays or failures are occurring in the connection path.

How it works

Traceroute sends packets with a Time to Live (TTL) value of 1. The first router decrements this to 0, discards the packet, and sends a "Time Exceeded" message back to the source. The tool then sends a packet with a TTL of 2. The first router decrements it to 1, forwards it, and the second router decrements it to 0, sending back a "Time Exceeded" message. This process repeats, with the TTL value increasing by one each time, until the packet reaches its destination. To determine when the final destination is reached, traceroute sends a packet with a port number that is likely to be unreachable. The destination server then sends back an "unreachable" message, allowing the tool to calculate the final hop's round-trip time.