Port 770: Unassigned — A ghost in the well-known range

Port 770 sits in the well-known port range (0-1023) but has no official service assigned by IANA. It's one of hundreds of port numbers that exist in the registry but remain unclaimed—a reserved parking space that nobody officially occupies.

What "Unassigned" Means

When IANA marks a port as unassigned, it means no organization has registered it for a specific service. Unlike port 80 (HTTP) or port 443 (HTTPS), which have clear purposes defined in RFCs, port 770 has no official documentation saying "this is what you use this port for."

This is more common than you might think. The well-known range contains 1,024 port numbers, but only a fraction have services everyone recognizes.

The Mac OS Mystery

Here's where it gets murky. Some network documentation claims port 770 was used by Mac OS X for RPC-based services, possibly related to NetInfo—the directory service that existed in Mac OS X versions before Leopard (10.5).¹ NetInfo handled network-wide configuration information like user accounts and groups.

But here's the problem: there's no clear RFC or official Apple documentation confirming this. NetInfo was deprecated in 2007 when Mac OS X Leopard replaced it with Directory Services. If port 770 was ever used for this purpose, the documentation disappeared along with the service itself.

Other sources simply list port 770 as unassigned with no known usage.²

Why Unassigned Ports Matter

Unassigned doesn't mean unused. Applications can—and do—run services on any port they choose. A developer might pick port 770 for a custom application. A network admin might configure internal services to use it. There's no central authority stopping them.

This is actually how many port assignments started. Someone built something, picked a port, the software became popular, and eventually IANA made it official. Port 770 just never had that moment.

What Might Be Listening

If something is listening on port 770 on your network, it's either:

1. Legacy software — Possibly old Mac OS X services that still run on ancient systems
2. Custom applications — Someone's internal tool using an available port number
3. Malware — Less common but possible, as unassigned ports can hide malicious services
4. Nothing — Most likely scenario for most networks

How to Check

On Linux or macOS:

# See if anything is listening on port 770
sudo lsof -i :770

# Or using netstat
netstat -an | grep :770

On Windows:

# Check for listeners on port 770
netstat -an | findstr :770

If you see something listening and you don't know what it is, investigate. Unassigned ports are perfect hiding spots for services that don't want attention.

The Bigger Picture

Port 770 represents something true about the Internet's infrastructure: not everything is documented. Not every port has a purpose. Some numbers sit empty in the registry, waiting. Others get used informally and never make it into the official records.

The well-known range (0-1023) was supposed to be the organized, well-documented part of the port system. But even here, there are gaps. Ports that were used once and forgotten. Ports that various sources claim for different purposes. Ports that simply sit empty.

Port 770 is one of those gaps—officially unclaimed, occasionally mentioned in connection with defunct Apple services, but ultimately just a number in a registry that nobody owns.