To use dnstop to monitor and display DNS server traffic on a FreeBSD system, you will need to install the dnstop package using the pkg package manager:
# pkg install dnstop
Once dnstop is installed, you can use it to monitor DNS traffic on a specific interface by running the following command:
# dnstop -i INTERFACE
Replace INTERFACE with the name of the network interface you want to monitor, such as eth0 or wlan0.
dnstop will display a real-time summary of DNS traffic on the specified interface, including the number of DNS queries and responses, the domains being queried, and the IP addresses of the DNS servers being used.
To stop dnstop, press CTRL-C.
You can also use the -l option to specify the number of lines to display, and the -s option to specify the number of seconds between updates. For example, to display 10 lines and update every 5 seconds, you can use the following command:
# dnstop -i INTERFACE -l 10 -s 5
For more information about using dnstop, you can refer to the dnstop man page by running man dnstop on the command line.