traceroute(8)

NAME

traceroute - print route IP packets follow going to a re

mote host

SYNOPSIS

traceroute [ options ] host [ size ]

DESCRIPTION

Traceroute attempts to trace the route an IP packet fol

lows 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 in

termediate router. Traceroute starts probing with a TTL of one,

and increments by one until an ICMP port unreachable reply is re

ceived. 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. Pa

rameter 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 on

ly available to the super-user (root).

-m max_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.

-p port

Start probing at an alternate UDP port (default

33434). Traceroute by default sends out UDP packets with in

creasing port numbers starting at port, and listens for ICMP er

rors 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.

-q n 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.

-s addr

Set source address of outgoing packets to addr,

given either as numeric IP address, or as hostname.

-t tos 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.

-w wait

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 sec

tion ENVIRONMENT below on how to fine tune the lookup.

-I proto

Send out probe packets using IP protocol proto,

given either as name or numerical value (default UDP). Some fea

tures 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 prob

lem.

-Q Report detailed statistics on the round trip times

at each hop (minimum / average +- standard deviation / maximum).

The values are given in milli seconds.

-S min_ttl

Set the time-to-live (TTL) value in the first pack

et sent out to min_ttl (default 1). This option determines the

first (nearest) host that will show up in the trace.

-T t 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 net

work 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 documenta

tion 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 bug

gy 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 Gate

way 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 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 vari

ables. By default, traceroute issues a whois query on the Routing

Assets Database (RADB) at whois.ra.net, which should be suffi

cient 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 includ

ed 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 par

allel probing. It is known as trACESroute or traceroute-nanog.

SEE ALSO

mtr(8), netstat(8), pchar(8), ping(8)

BUGS

Please send any bugs to Ehud Gavron <gavron@wetwork.net>

and/or report them to the Debian Bug Tracking System at

http://bugs.debian.org/traceroute-nanog.

AUTHORS

TrACESroute is maintained by Ehud Gavron <ehud.gavron@lo

gin.com>.

The first man page was written by Brian Russo for use with

Debian/GNU, and was later rewritten by Daniel Kobras <kobras@de

bian.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.

NANOG traceroute 6.3.10 March 2004

TRACEROUTE(8)