@(#) $Header: /Users/olsen/Code/cvs2svn-2010/os4-cvs-repository/contrib/roadshow/client-software/tcpdump-3.8.1/README,v 1.2 2004-09-22 15:40:54 olsen Exp $ (LBL)



TCPDUMP 3.8

Now maintained by "The Tcpdump Group"

See 		www.tcpdump.org



Please send inquiries/comments/reports to 	tcpdump-workers@tcpdump.org



Anonymous CVS is available via:

	cvs -d :pserver:cvs.tcpdump.org:/tcpdump/master login

	(password "anoncvs")

	cvs -d :pserver:cvs.tcpdump.org:/tcpdump/master checkout tcpdump



Version 3.8 of TCPDUMP can be retrived with the CVS tag "tcpdump_3_8rel1":

	cvs -d :pserver:cvs.tcpdump.org:/tcpdump/master checkout -r tcpdump_3_8rel1 tcpdump



Please send patches against the master copy to patches@tcpdump.org.



formerly from 	Lawrence Berkeley National Laboratory

		Network Research Group <tcpdump@ee.lbl.gov>

		ftp://ftp.ee.lbl.gov/tcpdump.tar.Z (3.4)



This directory contains source code for tcpdump, a tool for network

monitoring and data acquisition.  This software was originally

developed by the Network Research Group at the Lawrence Berkeley

National Laboratory.  The original distribution is available via

anonymous ftp to ftp.ee.lbl.gov, in tcpdump.tar.Z.  More recent

development is performed at tcpdump.org, http://www.tcpdump.org/



Tcpdump uses libpcap, a system-independent interface for user-level

packet capture.  Before building tcpdump, you must first retrieve and

build libpcap, also originally from LBL and now being maintained by

tcpdump.org; see http://www.tcpdump.org/ .



Once libpcap is built (either install it or make sure it's in

../libpcap), you can build tcpdump using the procedure in the INSTALL

file.



The program is loosely based on SMI's "etherfind" although none of the

etherfind code remains.  It was originally written by Van Jacobson as

part of an ongoing research project to investigate and improve tcp and

internet gateway performance.  The parts of the program originally

taken from Sun's etherfind were later re-written by Steven McCanne of

LBL.  To insure that there would be no vestige of proprietary code in

tcpdump, Steve wrote these pieces from the specification given by the

manual entry, with no access to the source of tcpdump or etherfind.



Over the past few years, tcpdump has been steadily improved by the

excellent contributions from the Internet community (just browse

through the CHANGES file).  We are grateful for all the input.



Richard Stevens gives an excellent treatment of the Internet protocols

in his book ``TCP/IP Illustrated, Volume 1''. If you want to learn more

about tcpdump and how to interpret its output, pick up this book.



Some tools for viewing and analyzing tcpdump trace files are available

from the Internet Traffic Archive:



	http://www.acm.org/sigcomm/ITA/



Another tool that tcpdump users might find useful is tcpslice:



	ftp://ftp.ee.lbl.gov/tcpslice.tar.Z



It is a program that can be used to extract portions of tcpdump binary

trace files. See the above distribution for further details and

documentation.



Problems, bugs, questions, desirable enhancements, etc. should be sent

to the address "tcpdump-workers@tcpdump.org".  Bugs, support requests,

and feature requests may also be submitted on the SourceForge site for

tcpdump at



	http://sourceforge.net/projects/tcpdump/



Source code contributions, etc. should be sent to the email address

"patches@tcpdump.org", or submitted as patches on the SourceForge site

for tcpdump.



Current versions can be found at www.tcpdump.org, or the SourceForge

site for tcpdump.



 - The TCPdump team



original text by: Steve McCanne, Craig Leres, Van Jacobson



-------------------------------------

This directory also contains some short awk programs intended as

examples of ways to reduce tcpdump data when you're tracking

particular network problems:



send-ack.awk

	Simplifies the tcpdump trace for an ftp (or other unidirectional

	tcp transfer).  Since we assume that one host only sends and

	the other only acks, all address information is left off and

	we just note if the packet is a "send" or an "ack".



	There is one output line per line of the original trace.

	Field 1 is the packet time in decimal seconds, relative

	to the start of the conversation.  Field 2 is delta-time

	from last packet.  Field 3 is packet type/direction.

	"Send" means data going from sender to receiver, "ack"

	means an ack going from the receiver to the sender.  A

	preceding "*" indicates that the data is a retransmission.

	A preceding "-" indicates a hole in the sequence space

	(i.e., missing packet(s)), a "#" means an odd-size (not max

	seg size) packet.  Field 4 has the packet flags

	(same format as raw trace).  Field 5 is the sequence

	number (start seq. num for sender, next expected seq number

	for acks).  The number in parens following an ack is

	the delta-time from the first send of the packet to the

	ack.  A number in parens following a send is the

	delta-time from the first send of the packet to the

	current send (on duplicate packets only).  Duplicate

	sends or acks have a number in square brackets showing

	the number of duplicates so far.



	Here is a short sample from near the start of an ftp:

		3.00    0.20   send . 512

		3.20    0.20    ack . 1024  (0.20)

		3.20    0.00   send P 1024

		3.40    0.20    ack . 1536  (0.20)

		3.80    0.40 * send . 0  (3.80) [2]

		3.82    0.02 *  ack . 1536  (0.62) [2]

	Three seconds into the conversation, bytes 512 through 1023

	were sent.  200ms later they were acked.  Shortly thereafter

	bytes 1024-1535 were sent and again acked after 200ms.

	Then, for no apparent reason, 0-511 is retransmitted, 3.8

	seconds after its initial send (the round trip time for this

	ftp was 1sec, +-500ms).  Since the receiver is expecting

	1536, 1536 is re-acked when 0 arrives.



packetdat.awk

	Computes chunk summary data for an ftp (or similar

	unidirectional tcp transfer). [A "chunk" refers to

	a chunk of the sequence space -- essentially the packet

	sequence number divided by the max segment size.]



	A summary line is printed showing the number of chunks,

	the number of packets it took to send that many chunks

	(if there are no lost or duplicated packets, the number

	of packets should equal the number of chunks) and the

	number of acks.



	Following the summary line is one line of information

	per chunk.  The line contains eight fields:

	   1 - the chunk number

	   2 - the start sequence number for this chunk

	   3 - time of first send

	   4 - time of last send

	   5 - time of first ack

	   6 - time of last ack

	   7 - number of times chunk was sent

	   8 - number of times chunk was acked

	(all times are in decimal seconds, relative to the start

	of the conversation.)



	As an example, here is the first part of the output for

	an ftp trace:



	# 134 chunks.  536 packets sent.  508 acks.

	1       1       0.00    5.80    0.20    0.20    4       1

	2       513     0.28    6.20    0.40    0.40    4       1

	3       1025    1.16    6.32    1.20    1.20    4       1

	4       1561    1.86    15.00   2.00    2.00    6       1

	5       2049    2.16    15.44   2.20    2.20    5       1

	6       2585    2.64    16.44   2.80    2.80    5       1

	7       3073    3.00    16.66   3.20    3.20    4       1

	8       3609    3.20    17.24   3.40    5.82    4       11

	9       4097    6.02    6.58    6.20    6.80    2       5



	This says that 134 chunks were transferred (about 70K

	since the average packet size was 512 bytes).  It took

	536 packets to transfer the data (i.e., on the average

	each chunk was transmitted four times).  Looking at,

	say, chunk 4, we see it represents the 512 bytes of

	sequence space from 1561 to 2048.  It was first sent

	1.86 seconds into the conversation.  It was last

	sent 15 seconds into the conversation and was sent

	a total of 6 times (i.e., it was retransmitted every

	2 seconds on the average).  It was acked once, 140ms

	after it first arrived.



stime.awk

atime.awk

	Output one line per send or ack, respectively, in the form

		<time> <seq. number>

	where <time> is the time in seconds since the start of the

	transfer and <seq. number> is the sequence number being sent

	or acked.  I typically plot this data looking for suspicious

	patterns.





The problem I was looking at was the bulk-data-transfer

throughput of medium delay network paths (1-6 sec.  round trip

time) under typical DARPA Internet conditions.  The trace of the

ftp transfer of a large file was used as the raw data source.

The method was:



  - On a local host (but not the Sun running tcpdump), connect to

    the remote ftp.



  - On the monitor Sun, start the trace going.  E.g.,

      tcpdump host local-host and remote-host and port ftp-data >tracefile



  - On local, do either a get or put of a large file (~500KB),

    preferably to the null device (to minimize effects like

    closing the receive window while waiting for a disk write).



  - When transfer is finished, stop tcpdump.  Use awk to make up

    two files of summary data (maxsize is the maximum packet size,

    tracedata is the file of tcpdump tracedata):

      awk -f send-ack.awk packetsize=avgsize tracedata >sa

      awk -f packetdat.awk packetsize=avgsize tracedata >pd



  - While the summary data files are printing, take a look at

    how the transfer behaved:

      awk -f stime.awk tracedata | xgraph

    (90% of what you learn seems to happen in this step).



  - Do all of the above steps several times, both directions,

    at different times of day, with different protocol

    implementations on the other end.



  - Using one of the Unix data analysis packages (in my case,

    S and Gary Perlman's Unix|Stat), spend a few months staring

    at the data.



  - Change something in the local protocol implementation and

    redo the steps above.



  - Once a week, tell your funding agent that you're discovering

    wonderful things and you'll write up that research report

    "real soon now".