TRACEROUTE(8) | System Manager's Manual | TRACEROUTE(8) |
traceroute
— print
the route packets take to network host
traceroute |
[-adeEFISdNnrvx ] [-A
as_server] [-f
first_ttl] [-g
gateway] [-i
iface] [-M
first_ttl] [-m
max_ttl] [-P
proto] [-p
port] [-q
nqueries] [-s
src_addr] [-t
tos] [-w
waittime] [-z
pausemsecs] host
[packetsize] |
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 size (in bytes) after the destination host name.
Other options are:
-a
-A
as_server-d
-D
-E
-e
-f
first_ttl-F
-g
gateway-i
iface-s
flag for another way to do this.)-I
-M
first_ttl-m
max_ttl-n
-P
prototraceroute
does not implement any special knowledge of their packet formats. This
option is useful for determining which router along a path may be blocking
packets based on IP protocol number. But see BUGS below.-p
porttraceroute
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.-q
nqueries-r
-s
src_addr-i
flag for another way to do this.)-S
-t
tosTOS
). 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
TIME_EXCEEDED
and
UNREACHABLE
s are listed.-w
-x
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
calculated). 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
pausemsecsThis 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 unreachable" (which means we got to
"host") or hit a max (which defaults to
net.inet.ip.ttl hops & can be changed with the
-m
flag). Three probes (changed 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), 64 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
A more interesting example is:
[yak 72]% traceroute allspice.lcs.mit.edu. traceroute to allspice.lcs.mit.edu (18.26.0.115), 64 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
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 !
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) software, 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),
!S (source
route failed), (fragmentation needed - the RFC1191 Path MTU Discovery value
is displayed),
!U or
!W
(destination network/host unknown),
!I (source
host is isolated),
!A
(communication with destination network administratively prohibited),
!Z
(communication with destination host administratively prohibited),
!Q (for this
ToS the destination network is unreachable),
!T (for this
ToS the destination host is unreachable),
!X
(communication administratively prohibited),
!V (host
precedence violation),
!C (precedence
cutoff 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, 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.
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.
When using protocols other than UDP, functionality is reduced. In
particular, the last packet will often appear to be lost, because even
though it reaches the destination host, there's no way to know that because
no ICMP message is sent back. In the TCP case,
traceroute
should listen for a RST from the
destination host (or an intermediate router that's filtering packets), but
this is not implemented yet.
The AS number capability reports information that may sometimes be inaccurate due to discrepancies between the contents of the routing database server and the current state of the Internet.
May 29, 2008 | BSD 4.3 |