The tcpdump utility displays the headers and contents of packets
    on the network that match a boolean expression (filter). If
    no filter is supplied all packets processed by tcpdump will be
    displayed. The the packets that are processed can also be written
    to a binary file for later examination and filtering.

    For complete information about using tcpdump, refer to the HP
    TCP/IP Services for OpenVMS Tuning and Troubleshooting guide.