2.11BSD/man/cat8/traceroute.0
TRACEROUTE(8) UNIX Programmer's Manual TRACEROUTE(8)
NAME
traceroute - print the route packets take to network host
SYNOPSIS
traceroute [ -m max_ttl ] [ -n ] [ -p port ] [ -q nqueries ]
[ -r ] [ -s src_addr ] [ -t tos ] [ -w ] [ -w waittime ]
_h_o_s_t [ _p_a_c_k_e_t_s_i_z_e ]
DESCRIPTION
The Internet is a large and complex aggregation of network
hardware, connected together by gateways. Tracking the
route one's packets follow (or finding the miscreant gateway
that's discarding your packets) can be difficult. _T_r_a_-
_c_e_r_o_u_t_e utilizes the IP protocol `time to live' field and
attempts to elicit an ICMP TIME_EXCEEDED response from each
gateway along the path to some host.
The only mandatory parameter is the destination host name or
IP number. The default probe datagram length is 38 bytes,
but this may be increased by specifying a packet size (in
bytes) after the destination host name.
Other options are:
-m Set the max time-to-live (max number of hops) used in
outgoing probe packets. The default is 30 hops (the
same default used for TCP connections).
-n Print hop addresses numerically rather than symboli-
cally and numerically (saves a nameserver address-to-
name lookup for each gateway found on the path).
-p Set the base UDP port number used in probes (default is
33434). Traceroute hopes that nothing is listening on
UDP ports _b_a_s_e to _b_a_s_e+_n_h_o_p_s-_1 at the destination host
(so an ICMP PORT_UNREACHABLE message will be returned
to terminate the route tracing). If something is
listening on a port in the default range, this option
can be used to pick an unused port range.
-r Bypass the normal routing tables and send directly to a
host on an attached network. If the host is not on a
directly-attached network, an error is returned. This
option can be used to ping a local host through an
interface that has no route through it (e.g., after the
interface was dropped by _r_o_u_t_e_d(8C)).
-s Use the following IP address (which must be given as an
IP number, not a hostname) as the source address in
outgoing probe packets. On hosts with more than one IP
address, this option can be used to force the source
address to be something other than the IP address of
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the interface the probe packet is sent on. If the IP
address is not one of this machine's interface
addresses, an error is returned and nothing is sent.
-t Set the _t_y_p_e-_o_f-_s_e_r_v_i_c_e in probe packets to the follow-
ing value (default zero). The value must be a decimal
integer in the range 0 to 255. This option can be used
to see if different types-of-service result in dif-
ferent paths. (If you are not running 4.4bsd, this may
be academic since the normal network services like tel-
net and ftp don't let you control the TOS). Not all
values of TOS are legal or meaningful - see the IP spec
for definitions. Useful values are probably `-t 16'
(low delay) and `-t 8' (high throughput).
-v Verbose output. Received ICMP packets other than
TIME_EXCEEDED and UNREACHABLEs are listed.
-w Set the time (in seconds) to wait for a response to a
probe (default 3 sec.).
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 30 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 gateway 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 3 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).
A sample use and output might be:
[yak 71]% traceroute nis.nsf.net.
traceroute to nis.nsf.net (35.1.1.48), 30 hops max, 56 byte packet
1 helios.ee.lbl.gov (128.3.112.1) 19 ms 19 ms 0 ms
2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 39 ms
5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 39 ms 39 ms 39 ms
6 128.32.197.4 (128.32.197.4) 40 ms 59 ms 59 ms
7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 59 ms
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8 129.140.70.13 (129.140.70.13) 99 ms 99 ms 80 ms
9 129.140.71.6 (129.140.71.6) 139 ms 239 ms 319 ms
10 129.140.81.7 (129.140.81.7) 220 ms 199 ms 199 ms
11 nic.merit.edu (35.1.1.48) 239 ms 239 ms 239 ms
Note that lines 2 & 3 are the same. This is due to a buggy
kernel on the 2nd hop system - lbl-csam.arpa - that forwards
packets with a zero ttl (a bug in the distributed version of
4.3BSD). Note that you have to guess what path the packets
are taking cross-country since the NSFNet (129.140) doesn't
supply address-to-name translations for its NSSes.
A more interesting example is:
[yak 72]% traceroute allspice.lcs.mit.edu.
traceroute to allspice.lcs.mit.edu (18.26.0.115), 30 hops max
1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
2 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 19 ms 19 ms
3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 19 ms
4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 19 ms 39 ms 39 ms
5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 20 ms 39 ms 39 ms
6 128.32.197.4 (128.32.197.4) 59 ms 119 ms 39 ms
7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 39 ms
8 129.140.70.13 (129.140.70.13) 80 ms 79 ms 99 ms
9 129.140.71.6 (129.140.71.6) 139 ms 139 ms 159 ms
10 129.140.81.7 (129.140.81.7) 199 ms 180 ms 300 ms
11 129.140.72.17 (129.140.72.17) 300 ms 239 ms 239 ms
12 * * *
13 128.121.54.72 (128.121.54.72) 259 ms 499 ms 279 ms
14 * * *
15 * * *
16 * * *
17 * * *
18 ALLSPICE.LCS.MIT.EDU (18.26.0.115) 339 ms 279 ms 279 ms
Note that the gateways 12, 14, 15, 16 & 17 hops away either
don't send ICMP "time exceeded" messages or send them with a
ttl too small to reach us. 14 - 17 are running the MIT C
Gateway code that doesn't send "time exceeded"s. God only
knows what's going on with 12.
The silent gateway 12 in the above may be the result of a
bug in the 4.[23]BSD network code (and its derivatives):
4.x (x <= 3) sends an unreachable message using whatever ttl
remains in the original datagram. Since, for gateways, the
remaining ttl is zero, the ICMP "time exceeded" is
guaranteed to not make it back to us. The behavior of this
bug is slightly more interesting when it appears on the des-
tination system:
1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 39 ms
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3 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 39 ms 19 ms
4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 19 ms
5 ccn-nerif35.Berkeley.EDU (128.32.168.35) 39 ms 39 ms 39 ms
6 csgw.Berkeley.EDU (128.32.133.254) 39 ms 59 ms 39 ms
7 * * *
8 * * *
9 * * *
10 * * *
11 * * *
12 * * *
13 rip.Berkeley.EDU (128.32.131.22) 59 ms ! 39 ms ! 39 ms !
Notice that there are 12 "gateways" (13 is the final desti-
nation) and exactly the last half of them are "missing".
What's really happening is that rip (a Sun-3 running Sun
OS3.5) is using the ttl from our arriving datagram as the
ttl in its ICMP reply. So, the reply will time out on the
return path (with no notice sent to anyone since ICMP's
aren't sent for ICMP's) until we probe with a ttl that's at
least twice the path length. I.e., rip is really only 7
hops away. A reply that returns with a ttl of 1 is a clue
this problem exists. Traceroute prints a "!" after the time
if the ttl is <= 1. Since vendors ship a lot of obsolete
(DEC's Ultrix, Sun 3.x) or non-standard (HPUX) software,
expect to see this problem frequently and/or take care pick-
ing the target host of your probes.
Other possible annotations after the time are !H, !N, !P
(got a host, network or protocol unreachable, respectively),
!S or !F (source route failed or fragmentation needed - nei-
ther of these should ever occur and the associated gateway
is busted if you see one). If almost all the probes result
in some kind of unreachable, traceroute will give up and
exit.
This program is intended for use in network testing, meas-
urement and management. It should be used primarily for
manual fault isolation. Because of the load it could impose
on the network, it is unwise to use _t_r_a_c_e_r_o_u_t_e during normal
operations or from automated scripts.
AUTHOR
Implemented by Van Jacobson from a suggestion by Steve Deer-
ing. Debugged by a cast of thousands with particularly
cogent suggestions or fixes from C. Philip Wood, Tim Seaver
and Ken Adelman.
SEE ALSO
netstat(1), ping(8)
Printed 11/26/99 February 28, 1989 4