

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!



