Selfhosted Linkage

Run a Minecraft server on your own PC and let friends join — even when port forwarding won't work. Your friends just install the modpack. No VPN app, no account, nothing to configure.

Get the mod Why can't my friends join?

The problem

If you're reading this, you probably already did everything right: you set up a server, it runs fine on your own computer, friends on the same Wi-Fi can join — but friends over the internet can't, and the "port forwarding" step from the tutorial just doesn't work. This is almost never your fault.

A 60-second recap of how joining is supposed to work. Your home has one address on the internet, your public IP (like a street address). Your server waits behind a numbered "door" called a port (25565). The tutorial had you set up port forwarding on your router — "send connections on port 25565 to my PC" — and give friends your IP. Their game connects to your-IP:25565, and that's it.

Why it fails today: the internet ran out of the old address type (IPv4), so most home ISPs stopped giving each customer their own. Instead they put you behind CGNAT — hundreds of homes share one public IP, inside the ISP's equipment you can't touch. So forwarding a port on your router does nothing: the address the world sees isn't yours. You can follow every tutorial perfectly and it still won't work, because the problem is upstream at your ISP.

How to confirm: check your router's "WAN" IP. If it starts with 100.64.–100.127., that's a shared CGNAT address. Or if an "open port check" site never sees your server, same conclusion.

Existing solutions

Two established approaches get around the address problem. Both work; each has a cost.

Tunnels & proxies — e.g. playit.gg

You run a small program that opens a tunnel to the provider; they give you a public address and relay all traffic through their servers to your PC.

• Good: the simplest setup there is — nothing on your router, works behind any CGNAT.
• Cost: every packet goes through a middleman, so speed and lag depend on their network, never a direct connection. Free tier is limited (~$3/mo to raise it) and needs an account.

Overlay VPNs — e.g. Tailscale, ZeroTier

A "VPN" here means a private virtual network. You install their app on each machine; they form a little network so your friend's PC and your server act like one LAN.

• Good: very good at direct connections; free even for a large group (Tailscale: 6 users, unlimited devices, and one shared machine can be handed to ~1,000 people); a shared friend reaches only that one machine.
• Cost: everyone needs an account and must install the app; and you're running a whole VPN just to play one server.

Direct vs relay

Every peer-to-peer option here — Tailscale, ZeroTier, and ours — works the same way underneath, and it decides whether you ever spend money.

The catch: the free public relays are shared and rate-limited — equally true of Tailscale's relays and the free relays our public mode uses. A direct connection is fast; a relayed one over free infrastructure can feel laggy.

Our approach

Selfhosted Linkage keeps the good part — Tailscale-class direct connections — and drops the friction. It uses iroh, peer-to-peer networking from the same family as Tailscale's, but built into the mod, not as a separate VPN.

• No account. Your server makes its own public key — a long random ID that is its identity. Friends dial that key. Nothing stores accounts; it's stateless.
• Nothing extra to install. The networking lives inside the modpack your friends already install — tick a box, paste a key.
• Direct first, relay only as fallback. Only your server is exposed — one port, not your machine.
• One download covers Windows, macOS (Intel & Apple Silicon) and Linux. Any modpack, any online-mode.

Public mode — the easy way

For almost everyone, this is the whole thing: no server to rent, no account.

You (the host) — once

1. Download the host agent for your OS (above) and run it next to your server.
2. It prints your server's public key.
3. Send that key to your friends, with your port (usually 25565).

Your friends — every time

1. Install the modpack (the mod's already inside — one file).
2. Multiplayer → Add Server → tick "Selfhosted Linkage."
3. Paste your public key as the address, the port in the port box → Join.

Self-hosted mode — advanced, only if a friend lags

Skip this unless the rule above sent you here. The fix is to run your own relay near that friend. It costs a few dollars a month.

What's a VPS?

A VPS is a small computer you rent by the month, running in a datacenter, always on with its own public address — the thing your home connection lacks. You control it over a secure remote connection called SSH. For a relay it does one light job, so the cheapest one is plenty.

What to look for

Any provider works — we don't endorse one. Two things matter:

• Location: the relay only helps if it's near the friend who needs it. Pick a region close to them.
• Bandwidth: the relay passes game traffic, so choose a plan with a generous data allowance — avoid ultra-cheap plans with tiny transfer caps.

The cheapest CPU/RAM tier is fine. Choose Ubuntu (22.04 or 24.04). You also need a name for it: point a subdomain from a cheap domain (any registrar) at the VPS's IP, or use a free DuckDNS subdomain — the HTTPS certificate is obtained automatically.

# 1. install Caddy (handles the HTTPS certificate automatically)
sudo apt update && sudo apt install -y debian-keyring debian-archive-keyring apt-transport-https curl
curl -1sLf 'https://dl.cloudsmith.io/public/caddy/stable/gpg.key' | sudo gpg --dearmor -o /usr/share/keyrings/caddy-stable-archive-keyring.gpg
curl -1sLf 'https://dl.cloudsmith.io/public/caddy/stable/debian.deb.txt' | sudo tee /etc/apt/sources.list.d/caddy-stable.list
sudo apt update && sudo apt install -y caddy

# 2. run the one-line relay installer
curl -fsSL https://linkage.blopybox.net/dl/linkage-relay-install.sh -o install.sh
sudo bash install.sh relay.example.com

sudo ./install.sh --relay-url https://relay.example.com --mc-addr 127.0.0.1:25565

# /etc/iroh-relay/webroot/.well-known/selfhosted-linkage.json
{ "version": 1, "servers": { "25565": { "transport": "iroh",
    "relay_url": "https://relay.example.com", "ticket": "PASTE-THE-TICKET-HERE" } } }

Self-hosted mode is entirely yours to run — not a service we operate for anyone.

What you install

• Players: one mod jar (Fabric or NeoForge) — nothing else.
• Host (public mode): a small agent that runs in the background and prints your key.
• Host (self-hosted, optional): a one-line installer for the Ubuntu VPS relay.

Everything is open source, and the networking is a thin wrapper over the stock iroh tools.