Extreme 7520 and Extreme 7720 switches can be stacked with themselves or they can also be stacked with each other using Native V400 stacking (SummitStack-V400), or Native-V400-Alternative-configuration (using the long range AOC optics). Both the Extreme 7520 and Extreme 7720 have the same capability in terms of feature scalability and the speed, so either of them can be the primary switch or the backup switch.