Port 2593: Ultima Online — The Port That Belongs to Britannia

What This Port Is

Port 2593 sits in the registered port range (1024–49151). These ports are administered by IANA, and organizations can formally register them for specific services. Port 2593 has never been registered. IANA lists it as unassigned.

In practice, it belongs to Britannia.

The Unofficial Use: Ultima Online Private Servers

Ultima Online, released by Origin Systems in 1997, was one of the first massively multiplayer online games. Players inhabited a persistent fantasy world called Britannia. The official servers still run today, maintained by Broadsword Online Games.

But alongside the official game, a parallel world exists: private shards — fan-operated servers running open-source emulator software. The dominant emulator, RunUO, chose port 2593 as its default. RunUO begat ServUO (forked in 2013), which inherited the same default. UOX3, another emulator lineage, followed suit. The port propagated across every tutorial, every forum thread, every port-forwarding guide written for aspiring shard operators over two decades.

Today, active public shards including UO Outlands, UOG Demise, and Age of Britannia all listen on port 2593 by default. ¹

The Ultima Online protocol is a proprietary binary protocol. Clients connect over TCP, authenticate with the login server, and receive a list of available shards. The emulators reverse-engineered this protocol well enough to support the original clients — and in some cases, the enhanced clients — without modification.

Why Unassigned Ports Matter

The registered port range was designed to reduce collisions — two services accidentally using the same port on the same machine. IANA registration is voluntary and free, but many communities never bother. They pick a number, document it informally, and rely on convention.

Port 2593 is a small example of how port assignment actually works in practice: not always through official channels, but through adoption. When enough software defaults to a number and enough operators forward it in their routers, the port becomes de facto assigned whether IANA agrees or not.

How to Check What's Using This Port

If you see port 2593 active on a machine you manage:

# On Linux/macOS — show what process is listening
sudo ss -tlnp | grep 2593
sudo lsof -i :2593

# On Windows
netstat -ano | findstr :2593

If you're running a home server and see inbound connections to this port from the Internet, someone is probing for an Ultima Online shard — or you're actually running one and forgot.