Port 238: Unassigned — A Reserved Space in the Well-Known Range

Port 238 has no official service assigned to it. Both TCP and UDP port 238 are marked as unassigned in the IANA Service Name and Transport Protocol Port Number Registry.¹

What This Means

Port 238 falls within the well-known ports range (0-1023), also called system ports. This is the most restricted tier of port numbers. Ports in this range are assigned by IETF Review or IESG Approval—the Internet's standards bodies have to bless any protocol that wants to claim one of these numbers.²

But port 238 has never been claimed. No RFC. No protocol. No service. Just an empty slot.

Why Well-Known Ports Go Unassigned

You'd think every number below 1024 would be taken by now. The Internet has been around since 1969. Surely we've run out of room in the most prestigious range.

We haven't. Hundreds of well-known ports remain unassigned. Some were reserved for protocols that never shipped. Others sit empty because the protocols that might need them haven't been invented yet. Still others remain available because the IETF is conservative—they don't hand out well-known ports easily.

Port 238 is one of these gaps. A reserved space. A number waiting for a purpose.

No Unofficial Use

Unlike some unassigned ports that have been quietly claimed by applications or malware, port 238 doesn't appear to have any common unofficial uses. It's genuinely quiet.

That doesn't mean nothing ever listens on port 238—any application can bind to any port—but it means there's no widespread pattern of software using this number.

How to Check What's Listening

If you want to see whether anything is listening on port 238 on your system:

Linux/Mac:

sudo lsof -i :238
# or
sudo netstat -tulpn | grep :238

Windows:

netstat -ano | findstr :238

If something appears, it's either a custom application or something unusual. Port 238 has no standard service that should be there.

Why Unassigned Ports Matter

The existence of unassigned ports in the well-known range is a feature, not a gap. It means the Internet's addressing system isn't frozen. New protocols can still emerge. New services can still claim space in the most visible tier of port numbers.

Port 238 is one of those available spaces. It's waiting for a protocol that might arrive tomorrow, or never.

Related Ports

• Port 0: Reserved, never used for actual services
• Ports 1-1023: Well-known ports range, where port 238 lives
• Ports 1024-49151: Registered ports (less restricted)
• Ports 49152-65535: Dynamic/ephemeral ports (unrestricted)