TD-W8970N 
Wireless N ADSL2+ Modem Router User Guide
)Note:
If you are not sure about the PPP IP extension and PPP Debug Mode etc. below, please don’t select these options.
¾MTU Size: Maximum Transmission Unit Size. Check this box then you can change the MTU size. The default MTU value is 1480 Bytes. It is not recommended that you change the default value unless required by your ISP.
¾Enable Fullcone NAT: It is a type of NAT, if not enabled, the default NAT will act.
¾Dial on demand (with idle timeout timer): The Router will cut off the Internet connection after it has been inactive for a specific period of time (idle timeout), and it will automatically
¾PPP IP extension: Select this option to get the public IP address from the PPP server to your PC, and the NAT and SPI Firewall will be closed. Sometimes you can think it as bridge while
PPPdialing in the router. It’s a special feature deployed by some ISP. Unless your ISP specifically requires this setup, do not select it.
¾Use Static IPv4 Address: If your ISP gives you a static WAN, Gateway and DNS IP address, select this option to enter them manually.
¾Enable PPP Debug Mode: Select this option to debug the PPP function and you can see many PPP log information in the System Log. Only PPP has this debug Mode.
¾Bridge PPPoE Frames Between WAN and Local Ports: Select this option to start PPP connection in your local PC.
¾Enable IGMP Multicast Proxy: IGMP (Internet Group Management Protocol) is used to manage multicasting on TCP/IP networks. Some ISPs use IGMP to perform remote configuration for client devices, such as the Router. The default value is disabled, and if you are not sure, please contact your ISP or just leave it.
5.Select a preferred wan interface as the system default gateway in Figure
Figure
6.Configure the DNS Server Addresses on the screen below and click Next.
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