Roku Support
posted this on July 22, 2010 18:02
On the back on your player—it’s a set of six 2-digit pairs separated by colons, e.g. 00:0D:0A:1H:3G:5C. One set is for the Ethernet connector and for the other for the wireless connector.
Alternatively, from the Roku home screen, select settings> player info. The addresses will be listed on-screen.