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TRACEROUTE
!!!TRACEROUTE
NAME
SYNOPSIS
DESCRIPTION
SEE ALSO
AUTHOR
BUGS
----
!!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 outgoing
probe packet.


__-F__


Set the


__-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
default used for TCP connections).


__-n__


Print hop addresses numerically rather than symbolically 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 ''base'' to ''base + nhops - 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 ''routed''(8C)).


__-s__


Use the following IP address (which usually is given as an
IP number, not a hostname) as the source address in outgoing
probe packets. On multi-homed hosts (those 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 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
integer 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 operating
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
-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
__


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


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


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


 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


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-__ (fragmentation needed - the
RFC1191 Path MTU Discovery value is displayed), __!X__
(communication administratively prohibited), __!V__ (host
precedence violation), __!C__ (precedence cutoff in
effect), or __!__ (ICMP unreachable code
__


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, it is unwise to use ''traceroute'' during
normal operations or from automated scripts.
!!SEE ALSO


pathchar(8), netstat(1), ping(8)
!!AUTHOR


Implemented by Van Jacobson from a suggestion by Steve
Deering. Debugged by a cast of thousands with particularly
cogent 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.
----
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