UsernameIpLock
UsernameIpLock stops an account from being used on a different machine by tying each username to the address it first joined from.
What it does
A player who joins for the first time has their username permanently bound to the connecting IP address. Later connections under that username from the same IP join normally. A connection under the same username from a different IP is rejected, and that new IP is banned, which makes impersonating an existing player from another machine effectively impossible on offline-mode servers.
The mod is a server-side Fabric mod, so only the server needs it and players join without installing anything. Server operators can configure the rule and manage bindings with commands that require operator level 3. Files are published for Fabric only, for 12 release versions, with 1.0.1 for 1.21.11 as the latest file. It is released under the Creative Commons Attribution No Derivatives 4.0 license and is not open source.
Key features
Username to IP binding
Each username is locked to the address it first joined from, and the binding is kept on the server.
Rejection of foreign IPs
A later login under a bound username from a different address is refused before the player enters.
Automatic IP banning
The address that attempted the mismatched login is banned, so repeated attempts from that machine fail.
Operator commands
Administrative commands, restricted to operator level 3, let admins manage the stored bindings.
Compatibility
Latest build for each game version and loader.
1.21.x12 of 12 versions with builds
Only full game releases are shown. This mod publishes no snapshot builds.
Use cases
Offline-mode servers
Servers that run without Mojang account authentication can use the binding to stop a second person from taking over a name.
Who it’s for: Server owners and administrators running offline-mode Minecraft servers who want usernames tied to one connection address.
Questions
Does UsernameIpLock need to be installed on players' computers?
What happens if a player changes internet connection?
Which commands does UsernameIpLock provide?
Which Minecraft versions does UsernameIpLock support?
In the catalog
UsernameIpLock is one of 5,392 Social mods on ModsFinder, and one of 4,084 Social mods for Fabric. 19,862 mods support Minecraft 1.21.11.
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What the author says
A server-side Fabric mod that prevents account takeovers on offline-mode Minecraft servers by binding each username to the IP address it first joined from. When a player joins for the first time, their username is permanently bound to their IP address. If the same username later connects from a different IP, that IP…
Official listing
- Modrinth page
- modrinth.com/mod/usernameiplock
- Owner
- notwinterdust
- Published
- 2025-11-18
- Updated on Modrinth
- 2026-06-12
- Facts verified
- 2026-10-15