Linux® Routing

traceroute

traceroute is likely only second to the ping command as the most often used network troubleshooting tool. traceroute shows the path between the source (the Linux node where the command is executed) and the destination.

traceroute, unlike ping, does not rely on the routers in the path responding to a particular path but rather assembles a UDP packet with the destination address—but with the time-to-live bits set to 1 for the first packet that is sent. traceroute then sends the packet, and the first router on the way to the destination accepts the packet and decrements the time-to-live. Because the time-to-live was 1, the time-to-live is now zero, which triggers the first router in the path to send back an ICMP time exceeded message ...