Use tcpdump & wireshark to show DNS traffic

1. Tcpdump

    Open a NEW connection to your master.grpX machine (log in a second
    time), so that you can have both windows side-by-side.

    In the new window, run the following command (you must be 'root', that's
    why we use sudo):

# sudo tcpdump -n -s 1500 udp and port 53

    This shows all packets going in and out of your machine for UDP port 53
    (DNS).
    
    Now go to another window and repeat some of the 'dig' queries from earlier.

    Look at the output of tcpdump, check the source and destination IP address
    of each packet:

Explanation:

    -n  Prevents tcpdump doing reverse DNS lookups on the packets it receives,
        which would generate additional (confusing) DNS traffic

    -s 1500 Read the entire packet (otherwise tcpdump only reads 96 bytes)

    udp and port 53
        A filter which matches only packets to/from UDP port 53

2. Tshark, Wireshark

** will be done as a demo **