i have some 3560G switches, which are running rapid-PVST+ .
Now i would like to integrate some older 3550s to this LAN. As far as i can see they are only capable of rapid PVST (without the +).
Do i have to switch back to the older PVST to use the 3550s with the 3560Gs ?
PVST was designed for use with ISL encapsualtion.
PVST+ was designed for use with 802.1q encapsulation.
The 3550 supports Rapid-PVST+ just as the 3560 switches do. Some of the literature can be a bit confusing but see attached link which clearly shows that Rapid-PVST+ is supported by 3550 switches.