TRACEROUTE(1M)TRACEROUTE(1M)NAMEtraceroute - print the route IPv4 and IPv6 packets take to a network host
SYNOPSIS
/usr/etc/traceroute [ -4 | -6 ] [ -g <addr> ] [ -l ] [ -m <max_ttl> ]
[ -M <min_ttl> ] [ -n ] [ -p ] [ -q <queries> ] [ -r ]
[ -s <src_addr> ] [ -t <tos> ] [ -w <waittime> ]
host [ datalen ]
DESCRIPTIONtraceroute is a dual-protocol (IPv4 and IPv6) network route tracing
utility, based upon the original tool of the same name developed by Van
Jacobsen. traceroute displays the route that IPv4 or IPv6 packets take
to a specified host, using the Time To Live (TTL) field (for IPv4) or Hop
Limit (HL) field (for IPv6) to provoke ICMP_TIMXCEED (IPv4) or
ICMP6_TIME_EXCEEDED (IPv6) messages at each node along the route. Unlike
other versions of traceroute, traceroute sends ICMP echo request probes
instead of UDP packets. By default, traceroute creates 3 probe packets
for each node and will trace up to 30 nodes, although these parameters
may be adjusted using the options below.
The options are:
-4 Choose the address family as AF_INET for resolving address of
destination host. Address family determines which protocol to use.
For this option, traceroute will use an IPv4 address associated with
the hostname. If none exists, traceroute will state that the host
is unknown and exit. It will not try to determine if an IPv6
address exists in the name service database.
-6 Choose the address family as AF_INET6 for resolving address of
destination host. For this option, traceroute will use an IPv6
address that is associated with the hostname. If none exists,
traceroute will state that the host is unknown and exit. It will
not try to determine if an IPv4 address exists in the name service
database. If neither -4 nor -6 is provided, then if the name of a
host is provided, not the literal IP address, and a valid IPv6
address exists in the name service database, traceroute will use
this address. Otherwise, if the name service database contains an
IPv4 address, it will try the IPv4 address. To override this
default behavior, either -4 or -6 (only one of them) has to be
provided. If both are provided, the last option is accepted and the
first one is ignored.
-g Specify a loose source routing route. Multiple nodes may be
specified using the -g option for each node. If one or more nodes
are specified using -g, loose source routing is enabled and either
IPv4 options or IPv6 extension headers are used to specify the
route. This is useful for asking how somebody else, at addr,
(either an IP address or a hostname) reaches a particular target.
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TRACEROUTE(1M)TRACEROUTE(1M)-l Print the value of the TTL or hop-limit field in each received
packet (this can be used to help detect asymmetric routing).
-m Set the maximum number of hops used in outgoing probe packets. The
default is 30 hops or the minimum TTL plus 1, whichever is larger.
-M Set the minimum number of hops used in outgoing probe packets. The
default is 1 hop.
-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 Ignored. For backwawrds compatibility with UDP based traceroute.
-q Set the number of probe packets to send. The default is 3 packets.
-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 (for
example, after the interface was dropped by routed(1M)).
-s Use the following IPv4 or IPv6 address 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 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 type-of-service (TOS) 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. This is only supported for
IPv4. Not all values of TOS are legal or meaningful: see the IP RFC
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
ECHO_REPLYs are listed.
-w Set the time (in seconds) to wait for a response to a probe (default
is 3 seconds).
traceroute tries to trace the route that an IPv4 or IPv6 packet would
take to a specified host by sending ICMP echo request probe packets that
will expire at each hop along the route. The choice of protocol used
depends on the address family of the destination host specified. By
setting the TTL or HL fields of the probe packets to some small value n
the packet will expire at hop number n generating an ICMP_TIMXCEED
message for IPv4 or an ICMP6_TIME_EXCEEDED message for IPv6, allowing
traceroute to identify the address of the host in question. Once the hop
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limit corresponds to the destination host, this host responds to the echo
request and the route tracing terminates. For each hop, three probes are
sent by default. This default may be changed using the -q option. The
default maximum hop limit tried is 30; this may be changed using the -M
option. For each hop a line is printed showing the TTL, address of the
gateway and round trip time of each probe. If the probe answers for one
TTL or HL come from different gateways, the address of each responding
system will be printed. If there is no response within a 3-second
timeout interval (changed with the -w flag), a ``*'' is printed for that
probe.
A sample use and output for an IPv4 host might be:
% 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
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
Notice that lines 2 and 3 are the same because of a buggy kernel on the
second hop system - lbl-csam.arpa - that forwards packets with a zero TTL
(a bug in the distributed version of 4.3BSD). 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:
% 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 * * *
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16 * * *
17 * * *
18 ALLSPICE.LCS.MIT.EDU (18.26.0.115) 339 ms 279 ms 279 ms
Notice that the gateways 12, 14, 15, 16 and 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_EXCEEDEDs.
The silent gateway 12 in the above example 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:
% traceroute rip.berkeley.edu
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 of the 12 ``gateways'' (13 is the final destination), exactly the
half of them are ``missing''. In this example, rip, a Sun-3 running Sun
OS3.5, is using the TTL from the arriving datagram as the TTL in its ICMP
reply. The reply will then time out on the return path, with no notice
sent to anyone since ICMP packets aren't sent for ICMP packets, until we
probe with a TTL that's at least twice the path length - that is, 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 some vendors ship obsolete or nonstandard software,
expect to see this problem frequently and/or take care selecting 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 - neither of these should ever occur, and
the associated gateway is broken if you see one). If almost all the
probes result in some kind of unreachable, traceroute will give up and
exit.
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(ttl=n!) indicates that the TTL value in the ICMP TIME_EXCEEDED packet
that we received was "unexpected". What we expect is that the value will
be (some initial value - the number of routers between us). In other
words, if the path from hop 5 to us is the same as the path from us to
hop 5, we expect to receive a TTL value of (some initial value - 4).
Unfortunately, there are several common "initial value"s for ICMP TTLs.
The most common are 255, 60, 59, 30, 29. (IRIX, 4.3BSD-tahoe and cisco
routers use 255, Proteon routers use either 59 or 29 depending on
software release, several other implementations use 60 and 30.)
Traceroute checks against all of these, making it hard to detect some
"off by one" routing asymmetries. If you want to see all the TTL values
in all the packets, use the -l option.
For example,
% traceroute-g 10.3.0.5 128.182.0.0
will show the path from the Cambridge Mailbridge to PSC while
% traceroute-g 192.5.146.4 -g 10.3.0.5 35.0.0.0
shows how the Cambridge Mailbrige reaches Merit, by using PSC to reach
the Mailbridge.
This program is intended for use in network testing, measurement, and
management. It should be used primarily for manual fault isolation. It
is unwise to use traceroute during normal operations or from automated
scripts due to the load it could impose on the network.
AUTHORS
Sam Manthorpe.
Portions of this man page are taken from the documentation of the
original BSD traceroute program, written by Van Jacobson, Steve Deering,
C. Philip Wood, Tim Seaver, and Ken Adelman.
SEE ALSOtraceroute (1M), netstat(1), ping(1M)
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