| 1 | Use tcpdump & wireshark to show DNS traffic |
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| 2 | |
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| 3 | 1. Tcpdump |
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| 4 | |
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| 5 | Open a NEW connection to your master.grpX machine (log in a second |
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| 6 | time), so that you can have both windows side-by-side. |
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| 7 | |
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| 8 | In the new window, run the following command (you must be 'root', that's |
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| 9 | why we use sudo): |
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| 10 | |
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| 11 | # sudo tcpdump -n -s 1500 udp and port 53 |
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| 12 | |
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| 13 | This shows all packets going in and out of your machine for UDP port 53 |
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| 14 | (DNS). |
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| 15 | |
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| 16 | Now go to another window and repeat some of the 'dig' queries from earlier. |
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| 17 | |
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| 18 | Look at the output of tcpdump, check the source and destination IP address |
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| 19 | of each packet: |
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| 20 | |
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| 21 | Explanation: |
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| 22 | |
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| 23 | -n Prevents tcpdump doing reverse DNS lookups on the packets it receives, |
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| 24 | which would generate additional (confusing) DNS traffic |
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| 25 | |
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| 26 | -s 1500 Read the entire packet (otherwise tcpdump only reads 96 bytes) |
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| 27 | |
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| 28 | udp and port 53 |
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| 29 | A filter which matches only packets to/from UDP port 53 |
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| 30 | |
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| 31 | 2. Tshark, Wireshark |
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| 32 | |
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| 33 | ** will be done as a demo ** |
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