The Internet is a large and complex aggregation of network hardware, connected together by gateways. The traceroute command tracks the route packets follow from gateway to gateway. The command uses the IP protocol `time to live' field and attempts to elicit an ICMP "time exceeded" response from each gateway along the path to a particular host. The only mandatory parameter is the destination host name or IP number. The default probe datagram length is 38 bytes, but you can increase this by specifying a packet size (in bytes) after the destination host name. This is useful when the -f option is given for MTU discovery along the route. You should start with the maximum packet size for your own network interface (if the given value is even bigger, traceroute attempts to select a more appropriate value). If no packet size is given when using the -f option, traceroute determines the initial MTU automatically. To track the route of an IP packet, traceroute launches UDP probe packets with a small ttl (time to live) and then listens for an ICMP "time exceeded" reply from a gateway. Probes start with a ttl of one and increase by one until either an ICMP "port unreachable" is returned (indicating that the packet reached the host) or the maximum number of hops is exceeded (the default is 30 hops and can be changed with the -m option). At each ttl setting, traceroute launches three probes (you can change the number with the -q option) and prints a line showing the ttl, address of the gateway, and round trip time of each probe. If the probe answers come from different gateways, traceroute prints the address of each responding system. If there is no response within a 3 second timeout interval (which you can change with the -w option), an asterisk (*) is printed for that probe. To prevent the destination host from processing the UDP probe packets, the destination port is set to an unlikely value. You can change the destination port value with the -p option, if necessary.