apex-network-rescue — DHCP Server

A minimal DHCP server written in Go using github.com/insomniacslk/dhcp.

Automatically configures the host Ethernet adapter with a static IP at startup and reverts it to its original settings (DHCP or previous static IP) when the server is stopped.

Requirements

• Go 1.21+
• Windows: must be run as Administrator (required to bind UDP port 67 and to run netsh to configure the adapter)

Build

go build -o apex-network-rescue.exe .

Usage

apex-network-rescue.exe [flags]

Flags:
  -restore     Restore the saved adapter configuration from a previous interrupted run, then exit
  -iface       string   Ethernet adapter name (default: auto-detect first wired adapter)
  -server-ip   string   IP to assign to the adapter; also used as gateway (default: 192.168.100.1)
  -range-start string   First IP in the assignable pool (default: 192.168.100.100)
  -range-end   string   Last IP in the assignable pool  (default: 192.168.100.200)
  -lease       duration Lease duration, e.g. 12h, 30m   (default: 24h)

Quick start

1. Connect your Windows machine to the target machine via an Ethernet cable.
2. Open an Administrator command prompt and run:

apex-network-rescue.exe

The CLI will ask you to acknowledge the adapter warning and confirm the Ethernet cable is connected. It will then:

• Auto-detect the first wired Ethernet adapter
• Save its current IP configuration
• Assign it the static IP 192.168.100.1 / 255.255.255.0
• Check whether the amplifier already has a reachable IP on the subnet and use it directly when found
• Start the DHCP server
• Wait for the client to answer ping and for TCP port 5678 to become reachable before attempting the WebSocket command
• Restore the original adapter configuration before exiting

The target machine will receive an address in 192.168.100.100 – 192.168.100.200 with:

• Gateway: 192.168.100.1
• DNS: 1.1.1.1, 8.8.8.8
• Lease: 24 hours

3. Press Ctrl+C to cancel. The adapter is automatically reverted to its original configuration (DHCP or previous static IP) when a saved state is available.

If you run the program from a non-Administrator shell, it exits with a console error instead of opening a Windows elevation prompt.

If the program is interrupted and leaves the adapter in an intermediate state, relaunch it as Administrator with:

apex-network-rescue.exe -restore

The console only shows user-facing prompts, progress, and plain errors. Detailed runtime logs are appended to apex-network-rescue.log next to the executable. If the app hangs, that file should show the last completed startup step.

Specifying the adapter manually

If auto-detection picks the wrong adapter, pass its name explicitly:

apex-network-rescue.exe -iface "Ethernet 2"

The adapter name is shown in Network Connections (ncpa.cpl).

Defaults at a glance

Setting	Default value
Server IP	192.168.100.1
Subnet mask	255.255.255.0 (/24)
Pool start	192.168.100.100
Pool end	192.168.100.200
Gateway	same as Server IP
DNS	1.1.1.1, 8.8.8.8
Lease time	24h

How it works

Step	What happens
1	Finds the Ethernet adapter (auto or -iface)
2	Saves the adapter's current IP config via netsh
3	Applies the static server IP via netsh
4	Binds the DHCP socket to the server IP (forces Windows to route broadcasts out the correct adapter)
5	Handles DISCOVER → OFFER → REQUEST → ACK and RELEASE
6	On Ctrl+C / SIGTERM: reverts the adapter and exits

Leases are held in memory only and are lost on restart.