tracen

tracen is a network diagnostic tool commonly found on Unix-like operating systems, including Linux and macOS. Its primary function is to trace the path that network packets take from a source computer to a destination. It achieves this by sending out packets with incrementally increasing Time To Live (TTL) values. Each router along the path decrements the TTL value. When a router receives a packet with a TTL of zero, it discards the packet and sends an ICMP "Time Exceeded" message back to the source. Tracen records the IP address and round-trip time of these intermediate routers, effectively mapping out the hops between two points on a network.

This information is invaluable for network troubleshooting. By observing the path, administrators can identify bottlenecks, pinpoint where packet loss is occurring, or diagnose connectivity issues. If a website is unreachable or slow, tracen can show at which router the connection is failing. It can also reveal the geographical location of the intermediate servers, providing a broader understanding of the network infrastructure. While effective, tracen primarily relies on ICMP messages, which some network devices may block or rate-limit, potentially leading to incomplete traces. Newer tools like mtr combine the functionality of tracen and ping to provide more robust and continuous network path analysis.