TrafShow continuously display the information regarding packet
traffic on the configured network interface that match the boolean
expression. It periodically sort and updates this information. It
may be useful for locating suspicious network traffic on the net.

To use TrafShow, your kernel must be rebuilt with the following line
added to your kernel config file (/sys/i386/conf/<YourMachine>):

pseudo-device   bpfilter        4       # Berkeley packet filter

The number of devices determines the maximum number of simultaneous
BPF clients programs runnable. See /sys/i386/conf/LINT for details.