My understanding (and please correct me if I'm wrong) is that if I am running PVST than I am running the standard 802.1d STP but on a per vlan basis, and if there is a trunk that ISL would be used across the trunk, (PVST+ is the same but uses 802.1q across the trunk). Anyway I am running PVST so I should be running 802.1d, but when I do a show spanning-tree active on one of my down stream switches, I see some of the ports roles listed as "Altn" which to me means Alternate, but this confuses me because Alternate is a role in RSTP, not STP. Are PVST and PVST+ not really running 802.1d? but instead also versions of rapid STP? Why does role alternate show up on a PVST configuration?