Port 820 — Unassigned (historically NetInfo)

What Range This Port Belongs To

Port 820 sits in the well-known ports range (0-1023), also called system ports. These are assigned by IANA through formal IETF processes and typically reserved for essential Internet services.¹

But port 820 has no official assignment. According to IANA's registry, ports 811-827 are marked "Unassigned."²

The NetInfo Connection

Here's where it gets interesting: port 820 wasn't always empty.

Older Mac OS X systems (pre-10.5) used ports in the 600-1023 range for RPC-based services, and port 820 was associated with NetInfo—a hierarchical distributed database that managed administrative data on NeXTSTEP, OpenStep, and early Mac OS X systems.³

NetInfo stored user accounts, group permissions, email configurations, NFS mounts, printer definitions, and other network resources. It was central to how Mac systems organized network services.

Then, in 2007, Apple released Mac OS X 10.5 Leopard—and NetInfo was gone. Completely replaced by Open Directory, which had been available since Mac OS X Server 10.2.⁴

Port 820 remained, but its tenant had moved out.

What This Means Today

If you scan a modern system and find port 820 open, you should investigate. It's not supposed to be listening. NetInfo is dead. If something is using this port, it's either:

• A legacy Mac system (pre-2007)
• Custom software that chose this port arbitrarily
• Something worth investigating with antivirus scanning

How to Check What's Listening

On Linux or Mac:

sudo lsof -i :820

On Windows:

netstat -ano | findstr :820

This will show you what process, if any, has claimed port 820.

Why Unassigned Ports Matter

The well-known range is finite—only 1,024 ports. IANA doesn't assign them lightly. Port 820's unassigned status means it's available for future standardization, but also means anyone can use it unofficially.

This creates ambiguity. When you see port 820 open, you can't immediately know what's behind it. There's no RFC to reference, no standard to check against. You have to look.

Unassigned ports are gaps in the map. Sometimes they're empty. Sometimes they're occupied by squatters. Sometimes, like port 820, they're haunted by services that used to exist.