Port 858: The ambiguous tenant — A well-known port with uncertain assignment

What Port 858 Is

Port 858 resides in the well-known ports range (0-1023), the section of the port number system that IANA reserves for system and standard services. Ports in this range typically require elevated privileges to bind to and are meant for established, widely-used protocols.

But port 858's status is unclear.

Some documentation suggests it was used by NetInfo, an RPC-based directory service that Apple used in Mac OS X for managing administrative data—user accounts, network configurations, printer settings.¹ NetInfo lived in the port range 600-1023, and port 858 may have been one of its addresses.

But NetInfo was removed from Mac OS X entirely in version 10.5 (Leopard), released in 2007, replaced by Open Directory.² If port 858 was ever NetInfo's home, that tenant left nearly two decades ago.

The official IANA registry doesn't clearly document port 858's current assignment status in readily accessible sources.³ It may be unassigned. It may be reserved. It may be in limbo—one of thousands of port numbers whose histories have been partially forgotten.

Why Ambiguous Ports Matter

The port number system contains 65,535 possible values. Not all of them have clear, well-documented stories. Port 858 is a reminder that the Internet's addressing system is a living document with gaps, historical artifacts, and questions without easy answers.

Unassigned or ambiguously assigned ports serve several purposes:

• They provide space for future protocol development
• They can be used for private, internal services that don't need global coordination
• They reveal the history of protocols that once mattered but have faded

What This Port Range Means

Being in the well-known ports range (0-1023) means:

• Privileged binding — On Unix-like systems, only root or privileged processes can bind to these ports
• Reserved for standards — These numbers are meant for IANA-assigned services, not random applications
• Historical significance — Even if unassigned now, placement in this range suggests someone once thought a service here mattered enough to request it

Checking What's Listening

If you want to see if anything is actually using port 858 on your system:

On Linux/macOS:

# See what's listening on port 858
sudo lsof -i :858

# Or using netstat
netstat -an | grep :858

On Windows:

# Check port 858
netstat -ano | findstr :858

If nothing appears, the port is silent. If something does appear, you've found either a legacy service, a custom application, or possibly malware using an obscure port to hide.

The Honest Truth

We don't know port 858's full story. The historical record is incomplete. It may have carried Apple's directory service. It may have been assigned to something else entirely. It may never have been officially assigned at all.

Some ports have RFCs, Wikipedia articles, decades of documentation. Port 858 has fragments, hints, and empty documentation pages.⁴

This is not a failure of the system. It's a feature of a system that's been evolving for over four decades, carrying both living protocols and the ghosts of services that once mattered.