1. Understanding the Mechanism: How ICS Enables Ethernet Sharing

When you enable ICS on your primary internet connection and designate an Ethernet port for sharing, Windows configures your PC to act like a basic router for the device(s) connected to that port:

• Network Address Translation (NAT): ICS uses NAT. This allows the device connected to your sharing Ethernet port (which will have a private IP address) to send traffic to the internet through your PC. Outgoing traffic appears to come from your PC’s main public IP address, and incoming responses are correctly routed back to the requesting device. This is essential for sharing a single public IP address among multiple devices.
• DHCP Server: Windows activates a mini-DHCP (Dynamic Host Configuration Protocol) server on the designated sharing Ethernet port. This server automatically assigns necessary network configuration details—specifically, a private IP address, subnet mask, gateway address, and DNS server addresses—to any device you plug into that port.
• Fixed Gateway IP: Critically, Windows assigns a static IP address, typically 192.168.137.1, to the Ethernet adapter that is sharing the connection (the private adapter). This address acts as the default gateway for the device receiving the shared connection. Important: Be aware that this 192.168.137.x subnet is fixed for ICS and cannot be easily changed. This can cause IP address conflicts if the network providing your PC’s internet connection also happens to use the 192.168.137.x range.

2. Prerequisites

• A Windows 11 PC with administrator privileges.
• At least two network adapters:
  • One adapter connected to the internet (the public/internet source adapter, e.g., Wi-Fi, another Ethernet port, cellular modem).
  • One physical Ethernet port intended for sharing the connection out (the private/sharing target adapter).
• A standard Ethernet cable.

3. Step-by-Step Configuration Guide

1. Access Network Connections: Press Win + R, type ncpa.cpl, and press Enter. This opens the legacy Network Connections control panel.
2. Identify Adapters: Locate the adapter currently connected to the internet (your public/internet source) and the Ethernet adapter you want to share to (your private/sharing target). Note their names (e.g., “Wi-Fi”, “Ethernet 2”).
3. Open Properties of Internet Source Adapter: Right-click on the adapter that has the internet connection you want to share. Select “Properties”. (Note: You will need administrator privileges to change these settings).
4. Navigate to the Sharing Tab: In the Properties window, click the ”Sharing” tab.
   • (If the Sharing tab is missing, it might be disabled by Group Policy, or the necessary Windows service (Internet Connection Sharing (ICS), service name: SharedAccess) might be disabled or not running. You can check service status by running services.msc).
5. Enable ICS: Check the box labeled ”Allow other network users to connect through this computer’s Internet connection.”
6. Select the Private Network Connection: This is the crucial step for Ethernet sharing. Once the first box is checked, the dropdown menu below it, labeled ”Home networking connection:”, becomes active. Click this dropdown and select the specific Ethernet adapter you intend to use for sharing the connection out (your private/sharing target adapter). Do not select the adapter that already has internet.
7. Apply Settings: Click ”OK”. Windows will likely display a notification stating that the adapter selected for “Home networking connection” will be set to use the IP address 192.168.137.1. This confirms ICS is being configured on that port. Click “Yes” or “OK” if prompted.

4. Connecting the Client Device

1. Plug one end of the Ethernet cable into the designated private/sharing target Ethernet port on your Windows 11 PC.
2. Plug the other end into the Ethernet port of the device needing internet access (e.g., another PC, console, smart TV).
3. Ensure the client device’s network settings for its Ethernet adapter are configured to ”Obtain an IP address automatically” and ”Obtain DNS server address automatically” (i.e., using DHCP).
4. The client device should shortly receive an IP address from your PC (e.g., 192.168.137.xxx) and gain internet access.

5. Important Considerations and Troubleshooting

ICS is powerful but can sometimes require troubleshooting:

• Performance: ICS routes all shared traffic through your host PC. This consumes CPU and network resources on the host and can result in lower throughput and higher latency compared to using a dedicated hardware router. The host PC’s performance directly impacts the shared connection’s quality.
• Firewalls: Both the Windows Defender Firewall and any third-party firewall/security software on the host PC must allow ICS traffic. If the connection doesn’t work, temporarily disabling the firewall on the host PC can help diagnose if it’s the cause. If so, you’ll need to configure firewall rules to permit traffic for ICS (specifically on the 192.168.137.x subnet).
• ICS Service: Ensure the “Internet Connection Sharing (ICS)” service (SharedAccess) is running. You can check this via the Services management console (services.msc). Its startup type should ideally be “Automatic” or “Manual,” and it should be in a “Running” state after enabling ICS.
• Client Configuration: Double-check that the client device connected via Ethernet is set to obtain IP and DNS settings automatically via DHCP. Static IP configurations on the client will not work unless manually configured for the 192.168.137.x subnet with 192.168.137.1 as the gateway.
• Restarts: Sometimes, simply restarting both the host PC and the client device after configuring ICS can resolve connection issues.
• IP Conflicts: As mentioned, ICS uses the fixed 192.168.137.x subnet. If your primary internet source network also uses this range, ICS will likely fail or cause network instability. There is no straightforward way to change the ICS subnet.
• Driver Issues: Outdated or corrupted network adapter drivers on the host PC can interfere with ICS. Ensure drivers for both the public and private adapters are up-to-date.
• Disabling ICS: To turn off sharing, go back to the Sharing tab in the properties of your public/internet source adapter and uncheck the ”Allow other network users…” box, then click ”OK”.

6. ICS vs. Network Bridging

It’s worth noting that ICS is distinct from another Windows feature called “Network Bridge.” While bridging also involves multiple adapters, it works differently: a bridge combines network segments into a single Layer 2 network (sharing the same IP subnet), whereas ICS uses Layer 3 routing (NAT) and DHCP to share one connection with devices on a separate, dedicated subnet (192.168.137.x). For sharing an internet connection to a device via Ethernet, ICS is typically the intended method.