Port 9: Discard
Port 9 is the Discard Protocol, a service that silently drops any data sent to it. Like other early diagnostic protocols, it was useful for testing but offers no value on a modern network and should stay closed.
TCP/UDPLegacy protocolsUnencrypted by defaultIANA assigned
| Port number | 9 |
|---|---|
| Service | Discard Protocol |
| Protocol | TCP/UDP |
| Category | Legacy protocols |
| Default encryption | No |
Security note. Port 9 is not encrypted by default. Restrict it to trusted networks, or use an encrypted alternative where one exists, to avoid exposing credentials and data in transit.
Frequently asked questions
What is port 9 used for?
Port 9 is the Discard Protocol, a service that silently drops any data sent to it. Like other early diagnostic protocols, it was useful for testing but offers no value on a modern network and should stay closed.
Is port 9 TCP or UDP?
Port 9 (Discard) uses TCP/UDP.
Is port 9 secure?
Port 9 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 9 on my firewall?
Only if you specifically need Discard. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.