5520 Series switches can stack with themselves using SummitStack-V160. 5520 Series switches can also be stacked with 5320 Series or 5420 Series switches using Alternate stacking (10G link running at HG), or with 5720 Series switches using Native V200 stacking (SummitStack-V200). When creating a mixed stack of 5720 Series and 5520 Series switches, the Primary and Backup nodes must be 5720 Series switches.