Traceroute is a network diagnostic tool used to trace the routes that packets take from one end to another across a network, Local (LAN) or Wide (WAN). It is used to visualize and understand the path the data packets follow as they traverse routers and network segments between source and destination.
When a traceroute is ran, it sends a series of ICMP (Internet Control Message Protocol) Echo Request messages with increasing Time-To-Live (TTL) values to its destination. The TTL is used to limit the number of hops (routers) the packet can traverse. Each hop made in the path decrements the TTL value and once the TTL reaches zero, an ICMP Time Exceeded message is sent back to the source.
Traceroute uses the ICMP Time Exceeded response messages to generate a list of the routers the packets passed through, mapping out the route from the source to its destination. It measures the round-trip times of each set of packets, indicating the latency between the source and each hop in the path.
Traceroute is valuable for troubleshooting networks, identifying bottlenecks, and understanding the topology between source and destination. It is available natively from most operating systems and can be used via third-party tools.