Status: Officially assigned (IANA well-known port)
Service: NetInfo
Protocol: TCP/UDP
Current reality: The service is extinct
What Port 857 Was For
Port 857 was assigned to NetInfo, Apple's proprietary directory service that managed local users, groups, and network configuration in Mac OS X.1 Every Mac running OS X 10.0 through 10.4 used NetInfo to answer questions like "who can log into this machine?" and "what groups does this user belong to?"
NetInfo originated at NeXT Computer Inc.—the company Steve Jobs founded after leaving Apple in 1985. When Apple acquired NeXT in 1997, NetInfo came along with the operating system that would become Mac OS X.2
How NetInfo Worked
NetInfo was an RPC-based (Remote Procedure Call) directory service. Applications and system components would query NetInfo over port 857 to retrieve information about users, groups, mounts, and other system configuration data.3
In the early Mac OS X releases (10.0-10.4), NetInfo handled everything: local accounts, network directories, even managing entire networks of Macs—similar to how Microsoft's Active Directory or Novell's eDirectory worked.4
Why NetInfo Disappeared
The problem: the rest of the world had standardized on LDAP (Lightweight Directory Access Protocol) for directory services. NetInfo was proprietary, incompatible, and increasingly isolated.5
Starting with Mac OS X Server 10.2 in 2002, Apple began transitioning to Open Directory, a standards-based directory service built on LDAP.6 With each release, NetInfo's role shrank. By 10.4, it was only managing local users and groups.
In Mac OS X 10.5 Leopard, released in October 2007, NetInfo was eliminated entirely. Not deprecated. Not hidden. Gone.7 Open Directory replaced it completely.
What This Means for Port 857
Port 857 remains officially assigned to NetInfo in the IANA registry, but the service no longer exists. You won't find anything listening on port 857 on modern systems unless someone is running extraordinarily old Mac OS X software (pre-10.5, released in 2007).
The port is a fossil—a numbered reminder of Apple's NeXT heritage and the transition from proprietary protocols to open standards.
Checking Port 857
To see if anything is listening on port 857 on your system:
On macOS/Linux:
On Windows:
You'll almost certainly find nothing. NetInfo has been dead for nearly two decades.
Why Unassigned Ports Matter
Port 857 isn't technically unassigned—it has an official IANA assignment. But it's effectively abandoned. This illustrates something important about the port system: assignments are permanent, but services come and go.
The well-known port range (0-1023) contains dozens of ports assigned to services that no longer exist or have been replaced. They remain in the registry as historical artifacts. Port numbers never get recycled—once assigned, they stay assigned, even when the service dies.
This is by design. It prevents confusion and conflicts. Even though NetInfo is extinct, port 857 won't be reassigned to something else. The Internet's namespace preserves its history.
The Legacy
NetInfo lasted exactly one decade in Mac OS X: from the public beta in 2000 to its removal in 2007. For users who never looked under the hood, it was invisible. For system administrators managing Mac networks in the early 2000s, it was essential—and its removal was a relief.
Port 857 is what's left: a number in a registry, pointing to nothing, reminding us that even infrastructure eventually becomes archaeology.
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