Traceroute is a UNIX communication program that is used to see the route packets take to network host. This program attempts to trace the route an IP packet would follow to some internet host by launching UDP probe packets with a small ttl (time to live) then listening for an ICMP "time exceeded" reply from a gateway. It starts its probes with a ttl of one and increase by one until it gets an ICMP "port unreachable" (which means it has got to "host") or hit a max of 30 hops.
Traceroute will start its probe using UDP port number 33434. Traceroute hopes that nothing is listening on UDP ports 33434 to 33463 at the destination host (so an ICMP PORT_UNREACHABLE message will be returned to terminate the route tracing).
Frequently asked questions