Port 736 — Unassigned well-known port

Port 736 is unassigned. It sits in the well-known ports range (0-1023) but has never been claimed by any protocol or service.

What This Means

The well-known ports (0-1023) were reserved by IANA in the early days of the Internet for essential services. These ports require system privileges to use and were meant for foundational protocols—things like HTTP, FTP, SSH, DNS.

Some ports were assigned immediately. Port 80 became HTTP. Port 443 became HTTPS. Port 22 became SSH.

Port 736 just never got assigned. It's been sitting there, reserved but unused, for decades.

The Well-Known Range

Ports 0-1023 are special:

• They require root/administrator privileges to bind on Unix-like systems
• They're managed directly by IANA
• They're meant for standardized, widely-used services
• Once assigned, they rarely change

But not every port in this range has a purpose. Port 736 is one of the gaps—a number that was reserved but never filled.

Could Something Be Using It Anyway?

Yes. Just because a port is unassigned doesn't mean nothing can use it. Any application can attempt to listen on port 736, though it would need elevated privileges since it's in the well-known range.

To check what's listening on port 736 on your system:

# On Linux/macOS
sudo lsof -i :736
sudo netstat -tulpn | grep :736

# On Windows
netstat -ano | findstr :736

If something appears, it's either:

• Custom software configured to use this port
• Malware (unassigned ports are sometimes used by malicious software precisely because they're not monitored)
• A service that picked an arbitrary port number

Why Unassigned Ports Matter

The existence of unassigned ports in the well-known range tells you something about how the Internet evolved. Not every idea became a protocol. Not every protocol that was planned actually got built. Not every service that seemed important in 1985 is still relevant today.

These gaps are breathing room. They're potential space. If a future protocol needs a well-known port number, ports like 736 are available. IANA can assign them through the RFC process.

For now, port 736 is just a number—reserved, official, and completely empty.

Related Ports

Port 736 is part of a cluster of unassigned ports in the 730s range. Ports 732-740 are all unassigned.¹ It's unclear why this particular range was never claimed, but the pattern suggests that whatever services were using nearby ports (like port 731, also unassigned) simply didn't expand into this space.