MAC addresses were designed to be fixed numbers that cannot be changed, and we may need to change it having our own personal reasons
Changing MAC address to work with your ISP
Most internet subscriptions allow the customer only with a single IP address. The Internet Service Provider (ISP) can assign one static permanent IP address to every customer. The ISP more commonly issues each customer dynamic IP address that may change each time the customer connects to the internet.
ISPs ensure that each customer receives only one dynamic address using several methods. Dial-up and many DSL services typically require the customer to log in with a username and password provide to them. Cable modem services, on the other hand do this by registering and tracking the MAC address of the device that connect to the ISP.
The device whose MAC address is monitored by an ISP can be either the cable modem, a broadband router, or the PC that hosts the internet connection. The customer is free to build a network behind this equipment, but the ISP expects the MAC address to match the registered value at all times.
Whenever a customer replaces that device, or changes the network adapter inside it, the MAC address of this new equipment will no longer match the registered at the ISP. The ISP will often disable the customer’s internet connection for security and billing reasons.
You can change MAC address through Cloning
Some people contact their ISP to request and update the MAC address associated with their subscription. This process works but takes time, and Internet service will be unavailable while waiting for the provider to take action.
A better way to quickly workaround this problem is by changing the MAC address on the new device so that it matches the address of the original device. While an actual physical MAC address cannot be changed in hardware, the address can be emulated in software. This process is called cloning.
Many broadband routers today support MAC address cloning as an advanced configuration option. The emulated MAC address appears to the service provider identical to the original hardware address. The specific procedure of cloning varies depending on the type of router, you can check product documentation for details.
MAC addresses and Cable Modems
In addition to MAC addresses tracked by the ISP, some broadband modems also track the MAC address of the host computer’s network adapter within the home network. If you swap the computer connected to the broadband modem, or change its network adapter, your cable internet connection may not function afterward.
In this case the MAC address cloning is not required. Resetting on both the cable modem and the host computer will automatically change the MAC address stored inside the modem.
Changing MAC addresses through the Operation System (OS)
Starting with Windows 2000, users can sometimes change their MAC address through the Windows My Network Places interface. This procedure does not work for all network cards as it depends on a certain level of software support built into the adapter driver.
In Linux and versions of Unix, the “ifconfig” also supports changing MAC addresses if the necessary network card and driver support exists
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