Section: Maintenance Commands (8)Updated: March 2004Local indexUp
NAME
traceroute - print route IP packets follow going to a remote host
SYNOPSIS
traceroute [ options ] host [ size ]
DESCRIPTION
Traceroute attempts to trace the route an IP packet follows to some
internet host. It finds out intermediate hops by launching probe packets
with a small time-to-live (TTL) value, and then listens for an ICMP reply
of time exceeded from an intermediate router. Traceroute starts
probing with a TTL of one, and increments by one until an ICMP
port unreachable reply is received. This means the probe either
got through to host, or hit the maximum TTL.
host is the only mandatory argument, and specifies the target
system, either as an IP address, or as a host name. Parameter
size determines the size of the probe packets in bytes.
OPTIONS
-a
Abort after 10 consecutive hops without an answer.
-d
Turn on socket level debugging. This option is only available to the
super-user (root).
-mmax_ttl
Set the maximum time-to-live (TTL) value that will be used for probing.
Hosts that are farther than max_ttl hops away will not be traced
(default 30).
-n
Report only IP addresses, but no hostnames.
-pport
Start probing at an alternate UDP port (default 33434). Traceroute
by default sends out UDP packets with increasing port numbers starting
at port, and listens for ICMP errors returned from remote hosts.
This scheme only works if there are no UDP servers listening on the
probed hosts in the range from port to port + max_ttl.
-qn
Send out n queries for each TTL (each intermediate host) (default
3).
-r
Set Dont Route option, advising routers to drop the packets. In other
words, only probe within the local subnet.
-saddr
Set source address of outgoing packets to addr, given either as
numeric IP address, or as hostname.
-ttos
Set the type-of-service field in the outgoing IP packets (default 0).
tos is valid in the range of 0 to 255.
-u
Use microsecond timestamps.
-v
Turn on verbose output.
-wwait
Set timeout for replies to wait seconds (default 5 sec). If no
ICMP reply is received within wait after a packet has been sent
out, the probe is considered as failed.
-A
Report the Autonomous System Number (ASN) at each hop. Roughly
speaking, the ASN tells which administration a router is subject to.
See RFC 1930 for all the details, and section ENVIRONMENT below on how
to fine tune the lookup.
-Iproto
Send out probe packets using IP protocol proto, given either as
name or numerical value (default UDP). Some features like parallel
probing are only available when using UDP.
-M
Determine the maximum transfer unit (MTU) along the path. See RFC 1191
for details.
-O
At each hop, perform a DNS lookup and report the owner as listed in the
SOA record.
-P
Send out multiple probes in parallel. The default behaviour probes each
hop in turn, starting from the nearest. Parallel mode is faster, but
less reliable. Many routers rate limit ICMP packets from a single host,
so dropouts are much more likely in parallel mode, and need not indicate
a networking problem.
-Q
Report detailed statistics on the round trip times at each hop (minimum /
average +- standard deviation / maximum). The values
are given in milli seconds.
-Smin_ttl
Set the time-to-live (TTL) value in the first packet sent out to
min_ttl (default 1). This option determines the first (nearest) host
that will show up in the trace.
-Tt
End each line with t instead of a newline. This comes in handy,
for example, when including traceroute's output in an HTML page.
-U
Move on to probing the next hop as soon as the first successful probe
arrives.
-$
Send out nothing but a single ping with a very large time-to-live.
DIAGNOSTICS
Usually the round trip time is printed for each probe at each hop.
Special symbols denote when something went wrong:
*
No reply received within wait seconds.
!
Reply arrived with a time-to-live value of one or lower.
!H
Received a reply telling that the destination host is unreachable.
!N
Received a reply telling that the destination network is unreachable.
!P
Received a reply telling that the desired protocol is unavailable.
!S
Received a reply telling that source routing failed. Should never
occur--unless the probed gateway is screwed.
!F
Received a reply telling that fragmentation is needed. Should never
occur--unless the probed gateway is screwed.
EXAMPLES
(This section is taken almost verbatim from the documentation in the
traceroute sourcecode.)
[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
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 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
(I start to see why I'm having so much trouble with mail to
MIT.) 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 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
destination) 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
until we probe with a TTL that's at least twice the path length.
I.e., rip is really only 7 hops away.
ENVIRONMENT
The lookup process of Autonomous System Numbers (ASN, see option
-A above) can be configured via several environment variables. By
default, traceroute issues a whois query on the Routing Assets Database
(RADB) at whois.ra.net, which should be sufficient in most cases.
Chances are that you don't want to change anything here, unless you know
very well what you are doing.
The contents of the following environment variables are limited to
100 characters at most. Any trailing characters are silently ignored.
If unset, compiled-in defaults are used.
RA_SERVER
Server to issue a RADB whois query on, given either as hostname, or
dotted-quad IP address. Defaults to whois.ra.net.
RA_SERVICE
TCP port to connect to on the whois server, given either as name or port
number. Defaults to whois.
The following variables determine how traceroute attempts to extract an
ASN from the whois reply.
DATA_DELIMITER
Each line containing an ASN starts with this tag. Defaults to
origin:.
The RADB may contain more than one entry for a given IP address. To
find out the correct entry, traceroute has to look up the subnet
that is the most specific to this IP.
ROUTE_DELIMITER
Each line containing a subnet entry starts with this tag. Defaults to
route:.
PREFIX_DELIMITER
The network IP and the prefix are separated by this tag. Defaults to
/.
NOTES
This is not the standard version of traceroute (as included in the netkit
package), but an alternative implementation maintained by Ehud Gavron. It
is based on the Van Jacobson/BSD traceroute, and includes additional
features including AS lookup, TOS support, microsecond timestamps,
path MTU discovery, and parallel probing. It is known as trACESroute or
traceroute-nanog.
The first man page was written by Brian Russo for use with Debian/GNU,
and was later rewritten by Daniel Kobras <kobras@debian.org> and
Martin A. Godisch <martin@godisch.de>. Some parts are taken from the
documentation in the source code. Still, this man page may be
used by others.