I'm reading some documentation from Cisco about HA campus design. This classical campus architecture has a couple of trunks connecting each access switch to a couple of redundant L3 switches, using HSRP. The two L3 distribution switches are connected by a L3 link. Here comes my doubt: since the link between the active HSRP switch and the standby one is a L3 link, why is STP used anyway? I mean, the configuration example i read shows that the active switch is also configured as STP root for the various VLANs, but I'm not sure this is really needed as it would be if the link between distribution switches were a L2 link. After all both trunks are forwarding and.... Thank you