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| wiki:tcpdump [2017/02/28 18:00] – external edit 127.0.0.1 | wiki:tcpdump [2023/03/21 20:14] (current) – walkeradmin |
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| ====== tcpdump ====== | ====== tcpdump ====== |
| | <color #db5f0b>Jan 2017 (Updated MApr 2017)</color> |
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| ---- | ---- |
| | tcpdump is a tool to capture IP Packets at a command line level, its similar to the PCAP used by Wireshark (Wireshark is just a GUI to control PCAP). I say just a GUI, its rather good and saying it is 'just' a GUI is a little harsh. |
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| tcpdump is a tool to capture IP Packets at a command line level, its similar to the PCAP used by Wireshark (Wireshark is just a GUI to control PCAP). I say just a GUI, its rather good and saying it is 'just' a GUI is a little harsh. | Originally, I was using <color #ed1c24>tcpdump</color> to capture IP traffic and write it to a file, and if this is what you wish to do, then go to the section on this page called <color #ed1c24>File Capture</color>. However if you just wish to view the <color #ed1c24>tcpdump</color> output on screen, then look at the section entitled <color #ed1c24>Screen Capture</color>. |
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| | ==== Screen Caputre ==== |
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| | To show the output of tcpdump on the screen, use the follwoing syntax. |
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| | tcpdump -i eth2 -nn |
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| | The <color #ed1c24>-i eth2</color> specifies the interface you wish to monitor. the <color #ed1c24>-nn</color> tells tcpdump not to resolve port numbers to names (so won't display the word 'ftp' where it sees port 21 for example). |
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| | This results in the following style output. |
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| | |
| | <file> |
| | 05:58:06.235597 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.235646 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.236112 IP 10.0.20.1.10000 > 239.0.200.1.10002: UDP, length 1316 |
| | 05:58:06.236238 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.236422 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.236521 IP 10.0.20.100.1234 > 239.0.100.1.1234: UDP, length 1316 |
| | 05:58:06.236595 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.236818 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.237060 IP 10.0.20.1.10000 > 239.0.200.1.10001: UDP, length 1316 |
| | 05:58:06.237211 IP 10.0.20.1.10000 > 239.0.200.1.10003: UDP, length 1316 |
| | 05:58:06.237402 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.237425 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.237524 IP 10.0.20.100.1234 > 239.0.100.1.1234: UDP, length 1316 |
| | 05:58:06.237598 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.237985 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.238063 IP 10.0.20.1.10000 > 239.0.200.1.10001: UDP, length 1316 |
| | 05:58:06.238213 IP 10.0.20.1.10000 > 239.0.200.1.10002: UDP, length 1316 |
| | 05:58:06.238425 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.238572 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.238599 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.239174 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.239423 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.239521 IP 10.0.20.100.1234 > 239.0.100.1.1234: UDP, length 1316 |
| | 05:58:06.239597 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.239741 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.240065 IP 10.0.20.1.10000 > 239.0.200.1.10001: UDP, length 1316 |
| | 05:58:06.240215 IP 10.0.20.1.10000 > 239.0.200.1.10002: UDP, length 1316 |
| | 05:58:06.240325 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.240423 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.240521 IP 10.0.20.100.1234 > 239.0.100.1.1234: UDP, length 1316 |
| | 05:58:06.240597 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.240916 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.241166 IP 10.0.20.1.10000 > 239.0.200.1.10003: UDP, length 1316 |
| | 05:58:06.241304 IP 10.0.20.1.10000 > 239.0.200.1.10004: UDP, length 1316 |
| | 05:58:06.241423 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | 05:58:06.241507 IP 10.0.85.1.60817 > 239.0.85.1.1234: UDP, length 1316 |
| | 05:58:06.241596 IP 10.0.20.1.1234 > 239.1.2.3.1234: UDP, length 1328 |
| | |
| | 18909 packets captured |
| | 18913 packets received by filter |
| | 0 packets dropped by kernel |
| | |
| | </file> |
| | \\ |
| \\ | \\ |
| | ==== File Capture ==== |
| \\ | \\ |
| On the MFEL, we can use tcpdump to capture either the <color red>IP Input</color> or the <color red>IP Output</color>. There are many commands available for tcpdump, and I will list some later on this page, but first lets just look at a working example, because this might be all you need for now. | On the MFEL, we can use tcpdump to capture either the <color red>IP Input</color> or the <color red>IP Output</color>. There are many commands available for tcpdump, and I will list some later on this page, but first lets just look at a working example, because this might be all you need for now. |
