Technical data

traceroute
traceroute
Displays the route that packets take to the network host.
Format
traceroute [-m max_ttl] [-n] [-p port] [-q nqueries] [-r] [-s src_addr] [-v] [-w waittime] host [packetsize]
Description
The Internet is a large and complex aggregation of network hardware connected
together by gateways. The traceroute command tracks the route that packets
follow from gateway to gateway. The command uses the IP protocol time-to-live
(TTL) 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 address. The
default probe datagram length is 38 bytes, but you can increase this value 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 1 and increment by one until either
an ICMP ‘‘port unreachable’’ is returned (indicating that the packet reached
the host) or until the maximum number of hops is exceeded (the default is 30
hops and can be changed with the
-m option). At each TTL setting, three probes
are launched (the number can be changed with the -q option), and traceroute
displays 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
displays the address of each responding system. If there is no response within a
3-second timeout interval (which can be changed with the -w option), traceroute
displays an asterisk (*) for that probe.
To prevent the destination host from processing the UDP probe packets, the
destination port is set to an unlikely value. If necessary, you can change the
destination port valued with the -p option.
Note
This program is intended for use in network testing, measurement,
and management. It should be used primarily for manual fault isolation.
Because of the load it could impose on the network, do not use traceroute
during normal operations or from automated scripts.
Flags
-A
Looks up the AS-number (autonomous system) for each hop’s network address at
the whois server specified by the -h option.
A–48 Troubleshooting Utilities Reference