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Unformatted text preview: the relative time of each packet from the start of the dump, and the time difference
between successive packets. We'll modify the output to show these two differences. The
first difference we print with six digits to the right of the decimal point when
microsecond resolution is available (two digits when only 10-ms resolution is provided),
and the second difference we print with either four digits or two digits to the right of the
decimal point (depending on the clock resolution).
In this text most tcpdump output was collected on the host sun, which provides microsecond
resolution. Some output was collected on the host bsdi running BSD/386 Version 0.9.4, which only
provided 10-ms resolution (e.g.. Figure 5.1). Some output was also collected on bsdi when it was
running BSD/386 Version 1.0, which provides microsecond resolution. tcpdump always prints the name of the sending host, then a greater than sign, then the
name of the destination host. This makes it hard to follow the flow of packets between
two hosts. Although our tcpdump output will still show the direction of data flow like
this, we'll often take this output and produce a time line instead. (The first of these in the
text is Figure 6.11.) In our time lines one host will be on the left, and the other on the
right. This makes it easier to see which side sends and which side receives each packet.
We add line numbers to the tcpdump output, allowing us to reference specific lines in
the text. We also add additional space between certain lines, to separate some packet
Finally, tcpdump output can exceed the width of the page. We wrap long lines around
at convenient points in the line.
As an example, the output produced by tcpdump corresponding to Figure 4.4 is shown file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/append_a.htm (5 of 7) [12/09/2001 14.47.59] Appendix A: The tcpdump Program in Figure A.3, assuming an 80-column terminal window.
We won't show our typing the interru...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12