What LAN Fence is — and is not

LAN Fence helps you notice when an unrecognised device joins a network you're responsible for, and collect evidence that may indicate unauthorized hardware, a rogue access point, or a supply-chain implant: a new MAC address, a vendor or hostname matching a known implant signature, or a locally-administered (spoofed) MAC where a legitimate device would show a vendor OUI.

LAN Fence only observes. It sends nothing beyond a standard ARP "who-has" request — the same request every device on your LAN sends routinely — and never touches, blocks, deauthenticates or spoofs anything on the network. It is a monitoring tool, not an enforcement one.

LAN Fence cannot prove that a device is malicious, or that a MAC address is genuine. MAC vendor prefixes and hostnames are trivially spoofed by anyone deliberately trying to blend in. A finding is a lead worth checking by hand, not a verdict. Use it as one input to your own judgement.

Licence

LAN Fence is released under the MIT License.

MIT License

Copyright (c) 2026 Stable State Consulting Ltd

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Third-party software and dependencies remain copyright of their respective authors and are subject to their respective licences, including the optional, GPL-2.0-only scapy dependency — see Third-party dependencies and the note on scapy.

Contributing

Contributions are welcome via pull requests on GitHub.

Contributions are expected to be distributed under the MIT License as part of LAN Fence.
Contributors retain copyright in their own contributions unless separately agreed in writing.
There is no Contributor Licence Agreement or copyright assignment to sign.
Add the source-file header to any new original source files: # Copyright (c) 2026-present Stable State Consulting Ltd / # SPDX-License-Identifier: MIT.
Do not submit a full copy of the IEEE OUI registry or similarly large generated data files — the packaged vendor table is a small, curated subset on purpose.

Scope: LAN Fence is a defensive, observation-only tool. Please do not propose features that add active exploitation, packet injection/deauth, DHCP/ARP spoofing, network blocking or throttling, or any other offensive capability against devices LAN Fence discovers — such pull requests will be closed.

Security & trust

Why you can trust LAN Fence and this website, what LAN Fence touches on your machine, how to verify your download, and how to report a vulnerability are all covered on the Security & trust page.

In short: report suspected vulnerabilities via a GitHub issue marked security or email [email protected].

Stable State Consulting Ltd

LAN Fence is built and maintained by Stable State Consulting Ltd (www.stablestate.co.uk). For project questions, use the GitHub repository.