Port 10566 — Unassigned, But Not Unused

The Range

Port 10566 lives in the registered port range (1024-49151). These ports exist for applications to request when they need a specific number. IANA maintains the registry. Port 10566 is listed in that registry as unassigned—no requester has officially claimed it.

Yet it carries traffic. That gap matters.

What Actually Uses It

NetApp storage systems use port 10566 for backup operations—specifically SnapMirror and SnapVault, which replicate data between storage arrays. DPX (a Catalogic backup solution) also communicates on this port between client systems and NetApp storage.¹²

Nobody filed an RFC for port 10566. Nobody formally registered it with IANA. The port simply became useful and stayed that way.

Why It Matters

The unassigned ports reveal something about how the Internet works in practice versus how it works in theory. IANA's registry is real and important, but it's not exhaustive. Applications choose ports based on what they need, what's available, what makes sense for their network. Some numbers get formally registered. Others just get used.

Port 10566 exists in that tension: officially unassigned, practically essential on networks that depend on NetApp backup systems.

How to Check What's On It

If you need to know what's listening on port 10566, the answer depends on your system:

On macOS or Linux:

lsof -i :10566
netstat -an | grep 10566
ss -tulpn | grep 10566

On Windows:

netstat -ano | findstr :10566
Get-NetTCPConnection -LocalPort 10566

From a network perspective: Use nmap to scan a host:

nmap -p 10566 [target-host]

The Bigger Picture

Registered ports (1024-49151) can be requested by anyone for any service. The fact that 10566 remains unassigned in the official registry doesn't mean it's unused or protected. It just means no one submitted the paperwork.

This matters for security: if port 10566 appears on your network and you're not running NetApp backup, something else is using it. The port isn't documented, so whatever's running there is invisible to standard port guides.

Check it. Know what's listening.