D-Link DIR-645 User Manual page 27

Section 3 - Software Configuration
Secondary DNS Enter the Secondary DNS IP address used here. This field is normally optional. Only one DNS address is required for a functional
Server: Internet connection, but using a second DNS address provides more stability.
MTU: Maximum Transmission Unit - you may need to change the MTU for optimal performance with your specific ISP. 1492 is the
default MTU.
MAC Address: The default MAC Address is set to the Internet port's physical interface MAC address on the Broadband Router. It is not
recommended that you change the default MAC address unless required by your ISP. You can use the Clone Your PC's MAC
Address button to replace the Internet port's MAC address with the MAC address of your Ethernet card.
D-Link DIR-645 User Manual 23