LAN Link

Share your Open-to-LAN world over the internet — e4mc style, without port forwarding.

LAN Link replaces Minecraft's "Open to LAN" window with an upgraded version: on top of the normal LAN options it can create a public tunnel to your world and post a shareable address in chat that your friends can use from anywhere.

Only you (the host) need this mod. Your friends just need vanilla Minecraft — any launcher works (cracked/non-premium included) — they paste the address into Multiplayer -> Direct Connection.

Features

The new Open to LAN window adds:

• Public Address (Internet) — creates a public relay tunnel and posts a join address in chat, e.g. a private domain like dilute-barista.ap.e4mc.link (the closest relay is picked automatically — Asia-Pacific for India). Friends paste it into Multiplayer -> Direct Connection. No port forwarding, no router setup, no accounts anywhere.
• Online Mode — on (default): only players signed in to their Minecraft account can join. Off: anyone can join with any username — classic offline LAN, cracked/non-premium launchers included.
• Max Players — set the player limit (vanilla LAN is locked to 8).
• Client Versions — let friends on older/newer Minecraft versions join (the mod translates between versions automatically — see below).
• Keeps hosting after you leave — quitting to the title screen no longer closes the world: friends stay connected and new friends can still join. A LAN Link button in the title screen's top-left corner lets you rejoin, copy the address, or stop and close the world (see Leaving the world).
• Plus the usual: LAN on/off, port, game mode for other players, allow cheats.

Safety nets built in:

• The primary path speaks the open QUIClime protocol (UDP/QUIC) to the e4mc relay network, which auto-selects the relay closest to you. For India that relay is ~70 ms away instead of bore.pub's ~260 ms in New Jersey.
• If the primary relay cannot be reached, LAN Link automatically falls back to the classic bore.pub relay (the numeric IP form is posted in chat, and if your ISP's DNS blocks or hijacks the relay's domain it is resolved over HTTPS via Google/Cloudflare DNS instead).
• Friends on the same Wi-Fi also get a direct 192.168.x.x:port address in the message, which bypasses the relay entirely for the best possible latency.
• If your internet connection has IPv6 (most Airtel/Jio/BSNL lines in India do), chat also shows a [2401:...]:port line. Friends whose internet is also IPv6 connect straight to you - no relay, no detour, the lowest possible latency.
• Leaving the world does not cut friends off — the LAN session and tunnel stop only when you stop hosting (title-screen button or Stop LAN) or close Minecraft.

Friend version support (nothing to install for them)

Your friends join with plain vanilla Direct Connect — the whole ViaVersion translation suite is bundled inside this mod:

• Older versions — friends on 1.9 and up (1.16.x, 1.20.x, 1.21.x, ...) can join your 26.2 world. 1.7/1.8 support exists upstream but may not connect reliably yet (known upstream bug — 1.9+ recommended).
• Newer versions — friends on 26.3 can join.
• Blocks/items from your world may look substituted on much older clients: an old client cannot show things that did not exist in its version (e.g. a newer block may appear as a similar older one).

The Client Versions toggles in the Open to LAN window control this live (no restart):

• Allow Older Clients off — old-version players are turned away with the standard "Outdated client! Please use 26.2".
• Allow Newer Clients off — new-version players are turned away with "Outdated server! I'm still on 26.2".

Blocked players also see the world as incompatible in their multiplayer list. Both toggles are remembered in config/lanlink.json.

Requirements

• Minecraft Java 26.2 with Fabric Loader 0.19.5+
• Java 25
• No Fabric API needed

Using it

1. Open your singleplayer world.
2. Press Esc -> Open to LAN (the multiplayer options button).
3. Leave Public Address: On (default), adjust Online Mode / Max Players / Client Versions if you like, and click Start LAN.
4. The chat posts the address — click it to copy, then send it to your friends.
5. When you want to take a break, just quit to the title screen: the world keeps running for friends. Rejoin from the LAN Link button (top-left) whenever you want.

Leaving the world (keep hosting for friends)

Quitting to the title screen keeps the world, the LAN session and the relay tunnel running:

• Friends who are already in the world stay connected.
• Friends can still join while you are at the title screen — the address keeps working.
• A LAN Link button in the top-left corner of the title screen opens the World open in background screen, where you can:
  • Rejoin world — jump straight back in, with everyone where they were.
  • Copy address — share it with someone new.
  • Stop and close it — saves and closes the world properly for everyone.

The world closes only when you stop it from that screen, use Stop LAN, or close Minecraft — all of which save the world fully. While it is running in the background, trying to open a different world shows the same screen instead, so two worlds never fight over the same port.

Prefer the old behaviour (leaving the world closes it)? Set "keepWorldRunningWhenLeaving": false in config/lanlink.json.

Connection quality

Remote connections go through a relay. LAN Link's default path uses the open e4mc relay network (QUIClime protocol): a broker picks the relay closest to you — for India that is the Asia-Pacific relay, roughly 70 ms away instead of bore.pub's ~260 ms in New Jersey.

• Friends on your Wi-Fi should use the 192.168.x.x:port address from the chat message: those connections go directly to your computer, no relay involved.
• For the absolute lowest latency, run your own relay on a small server near the players — see RELAY-SETUP.md. Set "useQuiclime": false in config/lanlink.json to make your own relay the primary path.
• Home connections behind CGNAT (common with Airtel/Jio) cannot accept incoming IPv4 connections at all, even with router port forwarding - but IPv6 is usually not CGNAT'd, so try the [2401:...]:port line first. If the friend's internet has no IPv6 either, a relay is the way around it.

Configuration

config/lanlink.json (created on first launch):

{
  "useQuiclime": true,
  "relayHost": "bore.pub",
  "relayPort": 7835,
  "allowOlderClients": true,
  "allowNewerClients": true,
  "keepWorldRunningWhenLeaving": true
}

useQuiclime (default true) uses the e4mc relay network as the primary path. Set it to false to prefer the classic bore relay configured by relayHost/relayPort — you can point those at any bore-compatible relay, including your own. The classic relay also runs automatically as a fallback whenever the primary path cannot connect.

allowOlderClients / allowNewerClients mirror the Client Versions toggles and are saved whenever you apply changes in the Open to LAN window.

keepWorldRunningWhenLeaving (default true) keeps the world and tunnel alive when you quit to the title screen. Set it to false if you want the world to close as soon as you leave it (the old behaviour).

Building

./gradlew build

Output jar: build/libs/lan-link-1.1.1.jar — drop it into your mods folder.

To test in the dev environment: ./gradlew runClient.

How it works

• The mod redirects the pause menu's "Open to LAN" button to its own screen (mixin on PauseScreen).
• Starting LAN publishes the integrated server (IntegratedServer.publishServer) with your chosen port, then opens a relay tunnel:
  • primary — QUIC (UDP) to the closest e4mc relay. The relay assigns a private domain and forwards each player connection over a QUIC stream to 127.0.0.1:lanPort (protocol: e4mc's open-source QUIClime / the e4mc network).
  • fallback — the classic bore TCP tunnel to bore.pub (or a relay of your choice).
• Online Mode maps to MinecraftServer.setUsesAuthentication, Max Players to a mixin on IntegratedServer.getMaxPlayers().
• Friend version translation is the ViaVersion suite (ViaFabric + ViaBackwards + ViaRewind) nested inside the mod jar; the Client Versions toggles set ViaVersion's blocked-version ranges (<26.2 / >26.2) at runtime when you apply changes.
• The public address is broadcast to all players and shown in chat with click-to-copy.
• Quitting to the title screen is intercepted (Minecraft.disconnectWithSavingScreen and Minecraft.disconnect mixins): instead of halting the integrated server, LAN Link keeps it ticking with the tunnel open, so friends stay connected and can still join. A title-screen button and the "World open in background" screen handle rejoining and stopping.
• Stopping from the title screen — or closing Minecraft — saves the world and shuts the integrated server and tunnel down cleanly.
• Tunnel sockets use TCP_NODELAY with 64 KiB copy buffers, so small game packets are forwarded immediately instead of being batched by the OS.

Version history

• 1.1.1 — UI polish: grouped settings with section headers, live tunnel status (connecting / active / failed), one-click copy with a "Copied!" confirmation, friend names and the same-Wi-Fi address on the background screen, and a green "running" indicator on the title-screen button.
• 1.1.0 — keep the world running for friends after you leave it; title-screen rejoin button and "World open in background" screen; UI fixes (equal-width buttons, all text clamped to the window).
• 1.0.1 — the Open to LAN window fits any window size / GUI scale; labels centred.
• 1.0.0 — first release: public shareable address (e4mc QUIClime relay + bore fallback), Online Mode toggle, Max Players, friend version support 1.9–26.3.

Credits

• QUIClime relay protocol, relay network and the QUIC codec fork: the open-source e4mc project (MIT; codec classes from its netty-incubator-codec-quic fork, Apache 2.0 — see libs/README.txt).
• Classic relay: bore by Eric Zhang.