What This Port Does
Port 3289 carries ENPC — Epson Network Peripheral Control — a proprietary UDP protocol that Epson uses to discover and communicate with network printers.
When you install an Epson printer driver or open EpsonNet Config (Epson's printer management tool), the software sends a UDP broadcast to 255.255.255.255:3289. It's the network equivalent of walking into a room and asking "any Epson printers in here?" Every Epson printer that hears the broadcast answers. The driver picks one and continues.
If you have an Epson printer on your network, it is almost certainly listening on UDP 3289 right now.
The Registered Port Range
Port 3289 sits in the registered port range (1024–49151). This range is where IANA tracks service assignments to prevent collisions — a port number gets associated with a specific application or protocol. Registered ports require no special OS privileges to open, unlike well-known ports (0–1023), which generally require root access.
ENPC's use of 3289 is de facto rather than formally standardized. The protocol is proprietary to Epson and not publicly documented. Developers who have tried to implement open-source ENPC support have had to reverse-engineer it from packet captures — there's a GitHub issue thread that reads like an archaeological dig through binary payloads.1
How to See What's Using It
To check if something on your machine is listening on 3289:
macOS / Linux:
Windows:
If you see an Epson process — EpsonNet, a printer driver, or scanner software — that's expected. If you see something else, it's worth investigating.
Why This Matters
Unassigned or informally-used ports reveal something true about how the Internet actually works: the formal registry and the real world don't always match. Protocols get deployed, hardware ships, millions of devices start listening — and the paperwork follows later, or never comes at all.
ENPC is a small example of a large pattern. The registered range is full of ports that have been quietly claimed by vendor protocols, legacy software, and de facto standards that predate or bypassed formal registration. The port number system is partly a registry and partly an archaeology site.
Security Note
ENPC uses UDP, which means there's no connection handshake — anyone on your local network can send a packet to a listening printer on 3289. The protocol is designed for LAN use, not exposure to the Internet. Epson printers should not have port 3289 reachable from outside your network perimeter.
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