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      1 @(#) $Header: /tcpdump/master/tcpdump/README,v 1.65.2.1 2007/09/14 01:03:12 guy Exp $ (LBL)
      2 
      3 TCPDUMP 3.9
      4 Now maintained by "The Tcpdump Group"
      5 See 		www.tcpdump.org
      6 
      7 Please send inquiries/comments/reports to 	tcpdump-workers (a] tcpdump.org
      8 
      9 Anonymous CVS is available via:
     10 	cvs -d :pserver:cvs.tcpdump.org:/tcpdump/master login
     11 	(password "anoncvs")
     12 	cvs -d :pserver:cvs.tcpdump.org:/tcpdump/master checkout tcpdump
     13 
     14 Version 3.9 of TCPDUMP can be retrieved with the CVS tag "tcpdump_3_9rel1":
     15 	cvs -d :pserver:cvs.tcpdump.org:/tcpdump/master checkout -r tcpdump_3_9rel1 tcpdump
     16 
     17 Please submit patches against the master copy to the tcpdump project on
     18 sourceforge.net.
     19 
     20 formerly from 	Lawrence Berkeley National Laboratory
     21 		Network Research Group <tcpdump (a] ee.lbl.gov>
     22 		ftp://ftp.ee.lbl.gov/tcpdump.tar.Z (3.4)
     23 
     24 This directory contains source code for tcpdump, a tool for network
     25 monitoring and data acquisition.  This software was originally
     26 developed by the Network Research Group at the Lawrence Berkeley
     27 National Laboratory.  The original distribution is available via
     28 anonymous ftp to ftp.ee.lbl.gov, in tcpdump.tar.Z.  More recent
     29 development is performed at tcpdump.org, http://www.tcpdump.org/
     30 
     31 Tcpdump uses libpcap, a system-independent interface for user-level
     32 packet capture.  Before building tcpdump, you must first retrieve and
     33 build libpcap, also originally from LBL and now being maintained by
     34 tcpdump.org; see http://www.tcpdump.org/ .
     35 
     36 Once libpcap is built (either install it or make sure it's in
     37 ../libpcap), you can build tcpdump using the procedure in the INSTALL
     38 file.
     39 
     40 The program is loosely based on SMI's "etherfind" although none of the
     41 etherfind code remains.  It was originally written by Van Jacobson as
     42 part of an ongoing research project to investigate and improve tcp and
     43 internet gateway performance.  The parts of the program originally
     44 taken from Sun's etherfind were later re-written by Steven McCanne of
     45 LBL.  To insure that there would be no vestige of proprietary code in
     46 tcpdump, Steve wrote these pieces from the specification given by the
     47 manual entry, with no access to the source of tcpdump or etherfind.
     48 
     49 Over the past few years, tcpdump has been steadily improved by the
     50 excellent contributions from the Internet community (just browse
     51 through the CHANGES file).  We are grateful for all the input.
     52 
     53 Richard Stevens gives an excellent treatment of the Internet protocols
     54 in his book ``TCP/IP Illustrated, Volume 1''. If you want to learn more
     55 about tcpdump and how to interpret its output, pick up this book.
     56 
     57 Some tools for viewing and analyzing tcpdump trace files are available
     58 from the Internet Traffic Archive:
     59 
     60 	http://www.acm.org/sigcomm/ITA/
     61 
     62 Another tool that tcpdump users might find useful is tcpslice:
     63 
     64 	ftp://ftp.ee.lbl.gov/tcpslice.tar.Z
     65 
     66 It is a program that can be used to extract portions of tcpdump binary
     67 trace files. See the above distribution for further details and
     68 documentation.
     69 
     70 Problems, bugs, questions, desirable enhancements, etc. should be sent
     71 to the address "tcpdump-workers (a] tcpdump.org".  Bugs, support requests,
     72 and feature requests may also be submitted on the SourceForge site for
     73 tcpdump at
     74 
     75 	http://sourceforge.net/projects/tcpdump/
     76 
     77 Source code contributions, etc. should be sent to the email address
     78 "patches (a] tcpdump.org", or submitted as patches on the SourceForge site
     79 for tcpdump.
     80 
     81 Current versions can be found at www.tcpdump.org, or the SourceForge
     82 site for tcpdump.
     83 
     84  - The TCPdump team
     85 
     86 original text by: Steve McCanne, Craig Leres, Van Jacobson
     87 
     88 -------------------------------------
     89 This directory also contains some short awk programs intended as
     90 examples of ways to reduce tcpdump data when you're tracking
     91 particular network problems:
     92 
     93 send-ack.awk
     94 	Simplifies the tcpdump trace for an ftp (or other unidirectional
     95 	tcp transfer).  Since we assume that one host only sends and
     96 	the other only acks, all address information is left off and
     97 	we just note if the packet is a "send" or an "ack".
     98 
     99 	There is one output line per line of the original trace.
    100 	Field 1 is the packet time in decimal seconds, relative
    101 	to the start of the conversation.  Field 2 is delta-time
    102 	from last packet.  Field 3 is packet type/direction.
    103 	"Send" means data going from sender to receiver, "ack"
    104 	means an ack going from the receiver to the sender.  A
    105 	preceding "*" indicates that the data is a retransmission.
    106 	A preceding "-" indicates a hole in the sequence space
    107 	(i.e., missing packet(s)), a "#" means an odd-size (not max
    108 	seg size) packet.  Field 4 has the packet flags
    109 	(same format as raw trace).  Field 5 is the sequence
    110 	number (start seq. num for sender, next expected seq number
    111 	for acks).  The number in parens following an ack is
    112 	the delta-time from the first send of the packet to the
    113 	ack.  A number in parens following a send is the
    114 	delta-time from the first send of the packet to the
    115 	current send (on duplicate packets only).  Duplicate
    116 	sends or acks have a number in square brackets showing
    117 	the number of duplicates so far.
    118 
    119 	Here is a short sample from near the start of an ftp:
    120 		3.00    0.20   send . 512
    121 		3.20    0.20    ack . 1024  (0.20)
    122 		3.20    0.00   send P 1024
    123 		3.40    0.20    ack . 1536  (0.20)
    124 		3.80    0.40 * send . 0  (3.80) [2]
    125 		3.82    0.02 *  ack . 1536  (0.62) [2]
    126 	Three seconds into the conversation, bytes 512 through 1023
    127 	were sent.  200ms later they were acked.  Shortly thereafter
    128 	bytes 1024-1535 were sent and again acked after 200ms.
    129 	Then, for no apparent reason, 0-511 is retransmitted, 3.8
    130 	seconds after its initial send (the round trip time for this
    131 	ftp was 1sec, +-500ms).  Since the receiver is expecting
    132 	1536, 1536 is re-acked when 0 arrives.
    133 
    134 packetdat.awk
    135 	Computes chunk summary data for an ftp (or similar
    136 	unidirectional tcp transfer). [A "chunk" refers to
    137 	a chunk of the sequence space -- essentially the packet
    138 	sequence number divided by the max segment size.]
    139 
    140 	A summary line is printed showing the number of chunks,
    141 	the number of packets it took to send that many chunks
    142 	(if there are no lost or duplicated packets, the number
    143 	of packets should equal the number of chunks) and the
    144 	number of acks.
    145 
    146 	Following the summary line is one line of information
    147 	per chunk.  The line contains eight fields:
    148 	   1 - the chunk number
    149 	   2 - the start sequence number for this chunk
    150 	   3 - time of first send
    151 	   4 - time of last send
    152 	   5 - time of first ack
    153 	   6 - time of last ack
    154 	   7 - number of times chunk was sent
    155 	   8 - number of times chunk was acked
    156 	(all times are in decimal seconds, relative to the start
    157 	of the conversation.)
    158 
    159 	As an example, here is the first part of the output for
    160 	an ftp trace:
    161 
    162 	# 134 chunks.  536 packets sent.  508 acks.
    163 	1       1       0.00    5.80    0.20    0.20    4       1
    164 	2       513     0.28    6.20    0.40    0.40    4       1
    165 	3       1025    1.16    6.32    1.20    1.20    4       1
    166 	4       1561    1.86    15.00   2.00    2.00    6       1
    167 	5       2049    2.16    15.44   2.20    2.20    5       1
    168 	6       2585    2.64    16.44   2.80    2.80    5       1
    169 	7       3073    3.00    16.66   3.20    3.20    4       1
    170 	8       3609    3.20    17.24   3.40    5.82    4       11
    171 	9       4097    6.02    6.58    6.20    6.80    2       5
    172 
    173 	This says that 134 chunks were transferred (about 70K
    174 	since the average packet size was 512 bytes).  It took
    175 	536 packets to transfer the data (i.e., on the average
    176 	each chunk was transmitted four times).  Looking at,
    177 	say, chunk 4, we see it represents the 512 bytes of
    178 	sequence space from 1561 to 2048.  It was first sent
    179 	1.86 seconds into the conversation.  It was last
    180 	sent 15 seconds into the conversation and was sent
    181 	a total of 6 times (i.e., it was retransmitted every
    182 	2 seconds on the average).  It was acked once, 140ms
    183 	after it first arrived.
    184 
    185 stime.awk
    186 atime.awk
    187 	Output one line per send or ack, respectively, in the form
    188 		<time> <seq. number>
    189 	where <time> is the time in seconds since the start of the
    190 	transfer and <seq. number> is the sequence number being sent
    191 	or acked.  I typically plot this data looking for suspicious
    192 	patterns.
    193 
    194 
    195 The problem I was looking at was the bulk-data-transfer
    196 throughput of medium delay network paths (1-6 sec.  round trip
    197 time) under typical DARPA Internet conditions.  The trace of the
    198 ftp transfer of a large file was used as the raw data source.
    199 The method was:
    200 
    201   - On a local host (but not the Sun running tcpdump), connect to
    202     the remote ftp.
    203 
    204   - On the monitor Sun, start the trace going.  E.g.,
    205       tcpdump host local-host and remote-host and port ftp-data >tracefile
    206 
    207   - On local, do either a get or put of a large file (~500KB),
    208     preferably to the null device (to minimize effects like
    209     closing the receive window while waiting for a disk write).
    210 
    211   - When transfer is finished, stop tcpdump.  Use awk to make up
    212     two files of summary data (maxsize is the maximum packet size,
    213     tracedata is the file of tcpdump tracedata):
    214       awk -f send-ack.awk packetsize=avgsize tracedata >sa
    215       awk -f packetdat.awk packetsize=avgsize tracedata >pd
    216 
    217   - While the summary data files are printing, take a look at
    218     how the transfer behaved:
    219       awk -f stime.awk tracedata | xgraph
    220     (90% of what you learn seems to happen in this step).
    221 
    222   - Do all of the above steps several times, both directions,
    223     at different times of day, with different protocol
    224     implementations on the other end.
    225 
    226   - Using one of the Unix data analysis packages (in my case,
    227     S and Gary Perlman's Unix|Stat), spend a few months staring
    228     at the data.
    229 
    230   - Change something in the local protocol implementation and
    231     redo the steps above.
    232 
    233   - Once a week, tell your funding agent that you're discovering
    234     wonderful things and you'll write up that research report
    235     "real soon now".
    236