Default Spanning Tree on Cisco IOS switches

Dilan77 used Ask the Experts™
Hi All

I've been searching the Cisco site for a definative answer as to what the default STP method is running on IOS switches such as the 2950 and 3550. Some people say it's PVST+, others CST.

Does anyone know, or better still, have a link to where this is answered?

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Top Expert 2015
PVST over ISL trunks and PVST+ over 802.1q trunks.

Same thing, basically.
Top Expert 2009
I second donjohnston's comment.

Speaking from experience with these switches, it's PVST+.

Here is a portion from this "" that confirms.  The link is for the 2950 switch but the same applies to the 3550.

Spanning-Tree Modes and Protocols

The switch supports these spanning-tree modes and protocols:

PVST+—This spanning-tree mode is based on the IEEE 802.1D standard and Cisco proprietary extensions. It is the default spanning-tree mode used on all Ethernet, Fast Ethernet, and Gigabit Ethernet port-based VLANs. The PVST+ runs on each VLAN on the switch up to the maximum supported, ensuring that each has a loop-free path through the network.


Thanks guys...

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