Port 670: VACDSM-SWS — The NetInfo ghost

Port 670 is officially assigned to VACDSM-SWS (VACDSM Switch Service), a Mac OS X RPC-based service that was part of NetInfo.¹²

But here's the strange part: NetInfo hasn't shipped with macOS since Mac OS X 10.5 Leopard in 2007. This port sits in the well-known range, officially assigned by IANA, serving software that no longer exists on modern systems.

What VACDSM-SWS Was

VACDSM-SWS ran on port 670 (both TCP and UDP) as part of Mac OS X's RPC (Remote Procedure Call) infrastructure.³ It worked alongside its sibling service VACDSM-APP on port 671, both serving NetInfo—Apple's proprietary directory service that managed system and network configuration information.

NetInfo was how early Mac OS X systems stored users, groups, network settings, and other configuration data. The VACDSM services handled communication between NetInfo processes across the network and on the local system.

When you had a Mac between 2001 and 2007, port 670 was actually doing something. It mattered.

Why This Port Is a Ghost

Apple replaced NetInfo with Open Directory in Mac OS X 10.5 (2007). Open Directory uses standard protocols like LDAP instead of proprietary RPC services. Port 670 became irrelevant overnight for millions of machines.

But the IANA assignment remains. Port 670 is still officially registered to VACDSM-SWS. It's a ghost—a port number reserved for software that no longer runs.⁴

This happens more than you'd think. Protocols get replaced, companies abandon technologies, services evolve beyond recognition. But port assignments are forever. Once IANA assigns a number in the well-known range, it stays assigned even when the service dies.

The Well-Known Range

Port 670 sits in the well-known port range (0-1023), which requires IANA Standards Action or IESG approval for assignment.⁵ These ports were meant for fundamental Internet services—things that would persist across decades.

Most do. Port 22 still carries SSH. Port 80 still carries HTTP. Port 25 still carries email.

But port 670 carries nothing except the memory of a directory service that served its purpose and was replaced by something better.

Checking Port 670

If you want to see if anything is actually listening on port 670 on your system:

On Linux or macOS:

sudo lsof -i :670

Or check listening services:

sudo netstat -an | grep :670

On Windows:

netstat -an | findstr :670

Unless you're running a very old Mac OS X system (10.4 or earlier), you'll find nothing. The port sits silent.

Why Unassigned Ports Matter

Port 670 isn't technically unassigned—it has an official service. But it's functionally unused, which raises a question: should obsolete port assignments be retired?

The well-known range only has 1,024 numbers (0-1023). Every ghost port like 670 is a number that can't be reused for something modern and relevant. The namespace is finite. History accumulates.

IANA doesn't retire port assignments lightly. Once a number is assigned, it generally stays assigned to prevent confusion and conflicts. Even if the original service is dead, reclaiming the port could break legacy systems or documentation.

So port 670 remains what it is: an officially assigned port serving obsolete software, a small monument to technology that served its purpose and moved on.

Related Ports

• Port 671 — VACDSM-APP, the sibling service that also served NetInfo
• Port 389 — LDAP, the standard directory protocol that partially replaced NetInfo
• Port 636 — LDAPS (LDAP over TLS), the secure version