PORT 9 – Information
Port Number: 9
TCP / UDP: UDP
Delivery: No
Protocol / Name: discard
Port Description: Discard. Port equiv to /dev/null. Reads pkts, then discards them. Allows knowledge the host is alive and processing pkts. Used while trouble-shooting local stack’s transmit ability (telnet to discard on remote host, knowing all transmitted keystrokes will just be discarded. no worry of corrupting host processes). No threat, but block on hosts and perimeter network devices as general rule.