Some ISP will register the MAC address of your computer when you dial up to Internet at the first time via modem. If you add a router into your network to share your Internet connection, ISP will not accept it, so you need to do MAC address clone on the router.
Note: Connect the computer which used to dialing up to the ADSL router, then configure it as below:
Step 1 Open web browser and type the IP address of the router (default is 192.168.1.1) into address bar, then press Enter.
Step 2 Type username and password into login page. The default username and password are both admin in lowercase.
Step 3 Click Advanced Setup->MAC Clone on left page.
Step 4 Click Clone MAN Address to clone your PC’s MAC address to WAN MAC Address of the ADSL router.
Step 5 Click Save/Reboot to save the settings and wait two minutes for the device’s rebooting.