The version of Spanning Tree Protocol the bridge is
currently running. The value 'stpCompatible(0)'
indicates the Spanning Tree Protocol specified in
IEEE 802.1D-1998 and 'rstp(2)' indicates the Rapid
Spanning Tree Protocol specified in IEEE 802.1w and
clause 17 of 802.1D-2004. The values are directly from
the IEEE standard. New values may be defined as future
versions of the protocol become available.
The value of this object MUST be retained across
reinitializations of the management system.