Port 3455: RSVP Port — Registered, Rarely Used

What This Port Is Registered For

IANA lists port 3455 (TCP and UDP) as "RSVP Port," assigned by Bob Braden — one of the original architects of the Internet's resource reservation work.¹

RSVP stands for Resource ReSerVation Protocol. It lets applications signal to routers along a network path that they need guaranteed bandwidth or latency — a Quality of Service (QoS) reservation. Before a video call starts, for example, RSVP could theoretically carve out a lane on the network, ensuring the audio doesn't drop when someone else starts downloading.

Here's the quirk: RSVP is defined in RFC 2205 as an IP-layer protocol, operating directly over IP (protocol number 46), not over TCP or UDP.² It doesn't need a port in the usual sense. The "RSVP Port" entry in IANA exists for implementations that tunnel RSVP messages through UDP — which some enterprise gear does — but it was never a mainstream Internet-facing service. If you see traffic on port 3455 today, it's almost certainly not RSVP.

What Actually Runs Here

The most common real-world use of port 3455 is for Painkiller, the 2004 first-person shooter developed by People Can Fly and published by DreamCatcher Interactive.³ The game's multiplayer uses TCP and UDP port 3455 for server connections. In the mid-2000s, Painkiller had a dedicated competitive scene — it was used in the 2005 Cyberathlete Professional League World Tour. Those players forwarded port 3455 a lot more than any network engineer ever configured RSVP.

Beyond that, there's no significant software ecosystem built around this port.

What Range This Port Belongs To

Port 3455 sits in the registered port range (1024–49151). IANA maintains this range for services and applications that have formally applied for an assignment. Having a registered port doesn't mean the protocol is widely deployed — it means someone filed the paperwork. The registered range is large enough that many entries reflect historical or niche uses, including protocols that never gained traction and applications that are long past their peak.

How to Check What's Listening on This Port

If you see activity on port 3455 and want to know what it is, these commands will tell you:

macOS and Linux:

sudo lsof -i :3455

Linux (alternative):

sudo ss -tulpn | grep 3455

Windows (Command Prompt, run as Administrator):

netstat -ano | findstr :3455
tasklist | findstr <PID>

These commands show you the process name and ID holding the port open. If nothing is listening, the port is closed and the output will be empty.