Port 2691: ITInternet ISM Server — A Name Without a Service

What Range This Port Belongs To

Port 2691 falls in the registered ports range: 1024–49151. These ports are managed by IANA and can be formally assigned to specific services. Unlike the well-known ports (0–1023), which require root or administrator privileges to bind, registered ports are accessible to any user process.

The registered range is enormous — over 48,000 ports — and a meaningful portion of it has never been claimed by anything widely used. Port 2691 is one of them.

The Name in the Databases

Several third-party port databases, including SpeedGuide and the SANS Internet Storm Center, list port 2691 as belonging to ITInternet ISM Server (service name: itinternet). ¹²

What is ITInternet ISM Server? That's where the trail goes cold. No RFC documents it. No widely-used software claims it. No vendor documentation surfaces with a credible explanation. The name exists in databases that have been copying each other's entries for decades, and it appears to originate from an era when small, proprietary servers routinely registered ports with IANA and then quietly disappeared.

In practice, treat port 2691 as unassigned. If you're seeing traffic on it, that traffic is specific to your environment — not a known protocol.

What the Scanners See

SANS ISC tracks scanning activity on this port, and multiple IPs probe it regularly. ² This is normal for unassigned ports in the registered range. Automated scanners don't know a port is empty until they check — so they check everything. The fact that port 2691 gets scanned says nothing about what's running there and everything about how thoroughly the Internet probes itself.

How to Check What's Listening on This Port

If you see traffic on port 2691 and want to know what's using it:

On Linux/macOS:

sudo ss -tlnp | grep 2691
sudo lsof -i :2691

On Windows:

netstat -ano | findstr :2691

Then cross-reference the process ID with Task Manager or ps to identify the application.

Why Unassigned Ports Matter

The registered port range exists so services can claim a consistent, predictable home. When port 22 opens a connection, you know SSH is there. When nothing is assigned to a port, that predictability disappears — any application can use it for any purpose, which is exactly what happens.

Unassigned ports become useful for:

• Custom internal services that need a consistent port without conflicting with known assignments
• Development environments where a service needs a temporary home
• Malware, which has historically favored unassigned ports precisely because they don't trigger pattern-based detection

Port 2691 has no documented malicious associations, but the principle holds: an unrecognized service on an unassigned port deserves investigation, not assumption.