Trace Route Test
Traceroute (tracepath on modern Linux systems, tracert on Windows operating system) is
a computer network tool used to determine the route taken by packets across an IP network.
Traceroute works by increasing the "time-to-live" value of each successive batch of
packets sent. The first three packets have a time-to-live (TTL) value of one
(implying that they make a single hop). The next three packets have a TTL value of 2,
and so on. When a packet passes through a host, normally the host decrements the
TTL value by one, and forwards the packet to the next host. When a packet with a
TTL of one reaches a host, the host discards the packet and sends an ICMP time
exceeded (type 11) packet to the sender. The traceroute utility uses these
returning packets to produce a list of hosts that the packets have traversed en
route to the destination. traceroute may not list the real hosts, it indicates that
the first host is at one hop, the second host at two hops. IP does not guarantee
that all the packets take the same route.
[see Wikipedia]