traceroute(8)

NAME

traceroute - print the route packets take to network host

SYNOPSIS

traceroute [ -dFIlnrvx ] [ -f first_ttl ] [ -g gateway ]
        [ -i iface ] [ -m max_ttl ] [ -p port ]
        [ -q nqueries ] [ -s src_addr ] [ -t tos ]
        [ -w waittime ] [ -z pausemsecs ]
        host [ packetlen ]

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. Traceroute 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 40 bytes, but
this may be increased by specifying a packet length (in bytes)
after the destination host name.
Other options are:
-f Set the initial time-to-live used in the first out
going probe packet.
-F Set the "don't fragment" bit.
-d Enable socket level debugging.
-g Specify a loose source route gateway (8 maximum).
-i Specify a network interface to obtain the source IP
address for outgoing probe packets. This is normally only useful
on a multi-homed host. (See the -s flag for another way to do
this.)
-I Use ICMP ECHO instead of UDP datagrams.
-l Display the ttl value of the returned packet. This
is useful for checking for assymetric routing.
-m Set the max time-to-live (max number of hops) used
in outgoing probe packets. The default is 30 hops (the same de
fault used for TCP connections).
-n Print hop addresses numerically rather than symbol
ically 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 (de
fault is 33434). Traceroute hopes that nothing is listening on
UDP ports base + 1 to base + nhops 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 de
fault 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 di
rectly-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
routed(8C)).
-s Use the following IP address (which usually is giv
en as an IP number, not a hostname) as the source address in out
going probe packets. On multi-homed hosts (those with more than
one IP address), this option can be used to force the source ad
dress to be something other than the IP address of the interface
the probe packet is sent on. This option can only be used by the
super-user. (See the -i flag for another way to do this.)
-t Set the type-of-service in probe packets to the
following value (default zero). The value must be a decimal in
teger in the range 0 to 255. This option can be used to see if
different types-of-service result in different paths. (If you
are not running 4.4bsd, this may be academic since the normal
network services like telnet 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 5 sec.).
-x Toggle ip checksums. Normally, this prevents
traceroute from calculating ip checksums. In some cases, the op
erating system can overwrite parts of the outgoing packet but not
recalculate the checksum (so in some cases the default is to not
calculate checksums and using -x causes them to be calcualted).
Note that checksums are usually required for the last hop when
using ICMP ECHO probes (-I). So they are always calculated when
using ICMP.
-z Set the time (in milliseconds) to pause between
probes (default 0). Some systems such as Solaris and routers
such as Ciscos rate limit icmp messages. A good value to use with
this this is 500 (e.g. 1/2 second).
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 unreach
able" (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 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).
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,; 38 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
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 bug
gy 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 ei
ther 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 destination 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
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 des
tination) 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) un
til 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) soft
ware, expect to see this problem frequently and/or take care
picking the target host of your probes.
Other possible annotations after the time are !H, !N, or
!P (host, network or protocol unreachable), !A, !C (access to the
network or host, respectively, is prohibited), !S (source route
failed), !F-<pmtu> (fragmentation needed - the RFC1191 Path MTU
Discovery value is displayed), !X (communication administratively
prohibited), !V (host precedence violation), !C (precedence cut
off in effect), or !<num> (ICMP unreachable code <num>). These
are defined by RFC1812 (which supersedes RFC1716). 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, mea
surement and management. It should be used primarily for manual
fault isolation. Because of the load it could impose on the net
work, it is unwise to use traceroute during normal operations or
from automated scripts.

DIAGNOSTICS

If your kernel does not support rtnetlink (routing mes
sages), you will get a warning of the form: traceroute: Warning: findsaddr: error sending; netlink message: <reason>
traceroute: Warning: ip checksums disabled
This is harmless as IP checksums will be provided by the
kernel, and UDP checksums (which are also disabled when rtnetlink
is unavailable) are optional.

AUTHOR

Implemented by Van Jacobson from a suggestion by Steve
Deering. Debugged by a cast of thousands with particularly co
gent suggestions or fixes from C. Philip Wood, Tim Seaver and Ken
Adelman.
The current version is available via anonymous ftp:: ftp://ftp.ee.lbl.gov/traceroute.tar.gz

BUGS

Please send bug reports to traceroute@ee.lbl.gov.
4.3 Berkeley Distribution 21 September 2000

docs.sk

comprehensive documentation repository

See also

traceroute(8)

NAME

SYNOPSIS

DESCRIPTION

DIAGNOSTICS

SEE ALSO

AUTHOR

BUGS