Below is a typical design that uses VSS to link two Core 6500 switches. All links are forwarding (no STP Loops), Access switches see the Core as one switch, HSRP does not apply and STP is turned off (Core is STP root). However, it isn’t blocking any links. For Dual Active Detection, a Direct Link is set up between the VSS pair. This is the recommended topology for 6500 based solutions (with a suitable Supervisor which supports VSS such as the Supervisor Engine 720-10G (VS-S720-10G-3C/XL)).