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
