D-Link DIR-655 User Manual page 22

Section  - Configuration
MTU: Maximum Transmission Unit - you may need to change the MTU for optimal performance with your specific ISP. 1400 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-655 User Manual