
Traceroute for Waterloo TCP/IP (DOS)

DESCRIPTION
-----------

Traceroute is a utility to trace the route of IP packets from the
current system to some destination system. See the comments at the
front of the program for a description of its use.

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 34 bytes, but this may be increased
by specifying a packet size (in bytes) after the destination host
name.

Usage: tracert [-?adDnVvQuOMAS] [-f min] [-g lsrr] [-h#] [-m max] [-p port]
               [-q nnum] [-s addr] [-w wait] [-t tos] host [datasize]


If you specify a number of bytes on the command line (datasize), that is
how big the entire packet will be, not just the data (as in traditional
traceroute).  This is due to problems with the -g option (which changes
the header length) and the -M option, which requires packets to really be
the size you say they are (and not 40 bytes bigger).  If the packet size
you ask for is too small, traceroute will silently make it the minimum size.


Other options are:
  -a  Loss Detection: Goes onto the next TTL if 10 consecutive
      packets are dropped.  Pressing <Control-C> will do the same
      thing if you want to get on to the next hop.

  -A  AS Path Lookup: This is what prtraceroute does.  It isn't
      implemented yet, though...  I'd like to put it in on the next
      go-round

  -g LSRR: This option allows you to add additional points in the path,
      giving the ability to (for example) traceroute to somewhere and
      back (so you can see the return path).  It is particularly useful
      in debugging split-routing type problems.  Note that you can put
      as many -g options in a traceroute as you want, up to the limit of
      the IP options space in the header.

  -M MTU Discovery: This option runs the algorithm in RFC1191 over
      the path in question.  Every packet is send out with the "Don't
      Fragment" bit set, and where necessary the packet size is reduced
      as per RFC1191.

  -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).

  -O  Owner Reporting: Report an email address for every hop. The addresses
      are taken from DNS SOA records, and usually have an address like
      "hostmaster@foo.bar.baz".  If you are using this for trouble reporting,
      it might be wise to look for an address like "noc" or "trouble" first,
      but at least this give a valid mail host and an address guaranteed to
      work if nothing else does.

  -p  Set the base UDP port number used in probes (default is 33450).
      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.

  -Q  Statistics Collection: This option reports the statistics on
      delay, (min, max, avg, and std. dev) instead of reporting individual
      transfer times.  It should be used with -q to send lots of packets to
      each hop to get good statistics.

  -s  Use the following IP address (which must be given as an IP number, not
      a hostname) 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' 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).

  -u  Microsecond Timers: This option reports times to microsecond
      accuracy (the default is millisecond accuracy).

      A warning about timers: Many machines have clocks with relatively
      large granularities.  I made no effort to do any better than what the
      standard system clock does.  Thus, in many cases, printing extra
      digits is of little use.  Also, some systems seem to do things like
      interrupt for screen writes, (which inconveniently can occur in the
      middle of timing a packet), causing further skew.  Still, on a quiet
      system, this may provide useful additional information.

  -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
      3.0 sec). The time can also be entered as a floating value, e.g `.5'
      is 0.5 sec.

  -h  Skip the hop with ttl equal number #. Useful for gateways or fire-
      walls which drops packets with TTL = 1.

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 "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
30 hops & can be changed with the \-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 3 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:

C:\WATT\BIN>tracert 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 bug in the distributed version of 4.3BSD).  Note
that 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:

C:\WATT\BIN>tracert 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 & 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 (with no notice sent to anyone since ICMP's
aren't sent for ICMP's) until we probe with a ttl that's at least twice
the path length.  I.e., 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 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, !P: got a host, network or protocol unreachable, respectively.
  !S, !F:     source route failed or fragmentation needed - neither of
              these should ever occur and the associated gateway is busted
              if you see one.

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.


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.

This release includes changes and additions made by Jamshid Mahdavi, Matt
Mathis, and Jon Boone.


CHANGES
-------

This release of traceroute is an updated version of Van Jacobson's
1988 release of the tool.  It includes all of the original features,
plus a number of things locally added at the PSC, and several
additions suggested by people on the NANOG list.

I changed the way packet sizes get allocated.  If you specify a number
of bytes on the command line, that is how big the entire packet will
be, not just the data.  This is due to problems with the -g option
(which changes the header length) and the -M option, which requires
packets to really be the size you say they are (and not 40 bytes
bigger).  If the packet size you ask for is too small, traceroute will
silently make it the minimum size.

The -w option will now default to 3 seconds and allow you to specify
wait times of < 1 second (i.e. .5 sec).  This is for those who get
sick of waiting for the *'s to show up...

All of the changes have been tested to some degree under Ultrix and
IRIX.  I hope that most of the bugs are out of them, but if there are
bugs on other OS's I'll update the release accordingly.  Happy
tracing!

