Port 3481: Unassigned — Microsoft Teams Screen Sharing (Unofficial)

What This Port Is

Port 3481 is unassigned. The Internet Assigned Numbers Authority (IANA) has not designated it for any official protocol or service.¹

It sits in the registered ports range (1024-49151), the middle tier of the port system. Well-known services live below 1024. Ephemeral, short-lived connections use ports above 49151. The registered range is where applications stake claims through IANA — or, in port 3481's case, don't bother and just use it anyway.

The Unofficial Reality

In practice, port 3481 belongs to a four-port family that Microsoft uses for real-time communication in Teams and Skype for Business:

When you share your screen on a Microsoft Teams call, your traffic flows out over UDP 3481 to Microsoft's edge servers. The division is intentional: audio, video, and screen content each have different tolerance for packet loss and latency, so Teams routes them separately rather than fighting over a single stream.²

This quartet (3478-3481) is documented in Microsoft's official network requirements. Every network admin preparing a corporate firewall for Teams is told to open these ports outbound. Millions of firewalls worldwide have rules for a port IANA never formally assigned.³

How to Check What's on This Port

If port 3481 shows up in your own traffic analysis, here's how to investigate:

See what's listening locally:

# macOS / Linux
sudo lsof -i :3481

# Windows
netstat -ano | findstr :3481

Capture and inspect traffic:

# Wireshark filter
udp.port == 3481

If you see UDP traffic on 3481 correlating with screen-sharing sessions, it's almost certainly Teams or Skype for Business. If you see TCP traffic on 3481, or activity outside of those applications, that's worth investigating — no official service owns this port, so anything using it is unofficial.

Why Unassigned Ports Matter

The port registry is not a law. It's a coordination system. Applications can and do use unassigned ports — sometimes quietly, sometimes at scale. Port 3481 is a small example of how the registered range works in practice: IANA maintains the list, but usage is driven by what ships in widely deployed software.

The consequence for network administrators is that "unassigned" doesn't mean "unused." Firewall rules, traffic analysis, and security monitoring all have to account for what's actually on the wire, not just what IANA's spreadsheet says.

Related Ports

• Port 3478 — STUN/TURN; the anchor of the Teams quartet
• Port 3479 — Teams audio (unofficial)
• Port 3480 — Teams video (unofficial)
• Port 443 — HTTPS; Teams fallback when UDP is blocked