Port 517: Talk
Port 517 is the Talk protocol, a Unix utility that let two users chat in real time in a split-screen text window. It has been replaced by modern messaging tools and is rarely run today.
| Port number | 517 |
|---|---|
| Service | Talk protocol |
| Protocol | UDP |
| Category | Legacy protocols |
| Default encryption | No |
How do I check whether port 517 is open?
Port 517 is UDP, which changes the answer: there is no handshake to complete, so nothing outside the host can prove the port is open. Asking the host itself is the reliable route.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | sudo nmap -sU -p 517 example.com | UDP has no handshake, so there is nothing to complete. nmap infers the state from whether an ICMP port-unreachable comes back, needs root, and is slow and easy to misread. A silent port may be open, filtered, or simply not replying to a probe it does not recognise. |
| What is listening locally? | ss -ulnp | grep ':517 ' | Shows the UDP socket bound to port 517. This is the reliable way to answer the question, because you are asking the host itself rather than guessing from outside. |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 517 used for?
Port 517 is the Talk protocol, a Unix utility that let two users chat in real time in a split-screen text window. It has been replaced by modern messaging tools and is rarely run today.
Is port 517 TCP or UDP?
Port 517 (Talk) uses UDP.
Is port 517 secure?
Port 517 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 517 on my firewall?
Only if you specifically need Talk. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.