How to use a computer as a router on your network?

Sometimes, we need to let a computer on the network do the action of a router, either for some specific action, or for testing. It turns out, that if you have a computer with Windows 10, for example, you don't need a router to share your internet with other computers due to integrated features that has existed since Windows XP: Internet Connection Sharing (ICS) does this automatically for you.

When using ICS, the windows firewall needs to be enabled and fully functional, as ICS is an integral part of the same core of applications that take care of the firewall.

Firewall is nothing more than the application that allows or blocks data from traveling through your computer, and when it becomes a network router, or "network gateway", all network data travels through your computer to others computers.

The default configuration allows your computer's "router" to automatically have: DNS, DHCP, and enable packet traffic through your computer, keeping in mind that you need to have at least two network connections, that is, the "WAN "and" LAN ".

Any network interface can be "WAN", you just have to choose which one you want to be "shared".

Remembering that this configuration, although it exists in some versions for Windows Server, if you have an application like RAS installed, these options may not be available, that RAS is the Windows Server packet routing system, and cannot run together with the ICS. RAS does not exist in Windows 10, 8, 7, XP, etc., because it is not intended for servers.

In the control panel, and in "Network and Sharing Center".

Click on the network adapter and click "properties".

On the "Sharing" tab, you will have the option to share your connection, in this case, the wired network, with the network adapter, in this example just called "Network", which can be your wi-fi connection, or a second card network.

Automatically this "home network" interface, that is, the adapter that users will connect to, will be configured with the following IP address:

IP: 192.168.137.1 (/ 24)

Mask: 255.255.255.0

So just put this second network interface connected to a switch or hub, and all other computers will have IP addresses in the range to have access to the network, and the gateway and DNS information will always be 192.168.137.1.

By default, Windows already configures only this IP address, but if you want to change it, there is no way to do this through the current options, because changing the IP on the interface, will not change the settings of the WAN table generated internally by ICS, ie , without communication, but it is possible to make this change in the Windows registry, to change both the firewall, as well as the configuration when sharing the network.

On record at:

HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Services \ SharedAccess \ Parameters

After the change, do not forget to restart the computer and everything will be working from the new IP.

However, there is no way to change the netmask, which remains locked to 255.255.255.0, that is, it supports a maximum of 256 devices, obviously zero, is the network identification and cannot be used, the first is the gateway , and the last is the broadcast address, leaving a maximum of 253 devices available to have access, which may be sufficient for, for example, a small business, even having equipment such as printers, IP cameras, among others.

If you need to configure something more precise, consider using Windows Server, and check with regard to the deployment of RAS to have full control of the scopes, DNS services, DHCP and addresses that will be assigned to your network.