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. We start our probes with a ttl of one and increase by one
until we get an ICMP "port unreachable" (which means we got to "host")
or hit a max (which defaults to net.inet.ip.ttl hops & can be changed
with the -m flag). Three probes (change with -q flag) are sent at each
ttl setting and a line is printed showing the ttl, address of the gate-
way and round trip time of each probe. If the probe answers come from
different gateways, the address of each responding system will be
printed. If there is no response within a 5 sec. timeout interval
(changed with the -w flag), a "*" is printed for that probe.
We don't want the destination host to process the UDP probe packets so
the destination port is set to an unlikely value (if some clod on the
destination is using that value, it can be changed with the -p flag).