Port 307: Unassigned — A Blank Space in the Well-Known Range

Port 307 is unassigned. Both TCP and UDP on port 307 have no official service assignment from IANA. The port exists, but nothing calls it home.

What This Means

The Internet's port space is divided into three ranges:

• Well-Known Ports (0-1023): System ports for fundamental Internet services, assigned by IETF Review or IESG Approval
• Registered Ports (1024-49151): User ports for specific applications, assigned by IANA
• Dynamic Ports (49152-65535): Ephemeral ports for temporary connections, not assigned

Port 307 sits in the well-known range. This is prime real estate in the port namespace—the range where SSH (22), HTTP (80), and HTTPS (443) live. But port 307 remains empty.

According to the IANA Service Name and Transport Protocol Port Number Registry, ports 301-307 are collectively listed as "Unassigned."¹ No service has ever claimed this port. No RFC defines a protocol for it.

Why Unassigned Ports Exist

Unassigned ports aren't accidents or oversights. They're deliberate gaps in the namespace, serving several purposes:

Future allocation pool — When someone designs a new protocol that needs a well-known port, unassigned ports are where they look. The Internet needs room to grow.

Resource conservation — RFC 6335 established procedures for port management, including how ports can move from assigned to unassigned status through de-assignment or revocation.² This prevents port number exhaustion.

Three-state system — Ports exist in three states: Assigned (actively used), Unassigned (available for assignment), and Reserved (held for special purposes like extending ranges).³ Unassigned ports form the available pool.

When RFC 6335 was written, approximately 76% of well-known ports were assigned. That means roughly 24% of ports in the 0-1023 range—including port 307—remain available for future needs.⁴

The Neighborhood

Port 307 sits between:

• Port 306: Unassigned (part of the 301-307 block)
• Port 308: novastorbakcup (Novastor Backup)

The entire 301-307 block is unassigned, making it one of the larger continuous gaps in the well-known port range.

How to Check What's Listening on Port 307

Even though port 307 has no official assignment, something on your system might be using it. Here's how to check:

On Linux/macOS:

# Using ss (modern)
sudo ss -tulpn | grep :307

# Using netstat (legacy but widely available)
sudo netstat -tulpn | grep :307

# Using lsof
sudo lsof -i :307

On Windows:

netstat -ano | findstr :307

If you see output, something is listening on or connected to port 307. The command will show you which process (PID) is using it.⁵

Should You Use Port 307?

For production services? No. Unassigned well-known ports should remain available for official assignment. If you need a port for a custom application, use the registered range (1024-49151) or dynamic range (49152-65535).

For testing or internal tools? Maybe. If you're running a private service on a closed network, an unassigned port won't conflict with anything standard. But document what you're doing—future you (or future someone) will appreciate knowing why port 307 suddenly has traffic.

For a protocol you're standardizing? Yes. If you're writing an RFC and need a well-known port, unassigned ports like 307 are exactly what the application process exists for.⁶

The Empty Space Matters

Port 307 isn't assigned because not every possible port needs a service. The Internet was designed with breathing room. In 1972, when ports were first conceptualized, nobody knew we'd eventually need HTTPS (443), or SMTP (25), or thousands of other protocols. The unassigned ports are the Internet's way of admitting it doesn't know what's coming next.

Port 307 is a blank page. Maybe it'll stay blank forever. Maybe in 2035 someone will write an RFC assigning it to a protocol we can't imagine yet. Either way, the space exists.

The Internet is 65,535 doors. Most are labeled. Port 307 is one of the few still waiting for a name.