Revision as of 08:47, 24 August 2011

Spanning Tree Protocols

DEC STP

Invented in 1985 by Radia Perlman at the Digital Equipment Corporation.

802.1D

Published in 1990 by the IEEE and based on the algorithm design by Perlman. Subsequent versions were published in 1998 and 2004 incorporating various extensions.

Common Spanning Tree(CST)

Common Spanning Tree(CST) assumes one 802.1D spanning-tree instance for the entire bridged network, regardless of the number of VLANs. Maintains only one instance of STP and therefor uses less CPU and memory than other STP varieties.

Per VLAN SPanning Tree Plus(PVST+)

PVST+ is a Cisco enhancement of STP that provides a separate 802.1D spanning-tree instance for each VLAN configured in the network. The separate instance supports enhancement such as PortFast, BPDU guard, BPDU filter, root guard, and loop guard. One instance per VLAN requires more CPU and memory than CST.

Rapid STP(RSTP)

IEEE 802.1w is an evolution of STP that provides faster convergence of STP. This version addresses many of the convergence issues in STP. It only maintains one RSTP instance per STP domain.

Multiple Spanning Tree(MST)

MST is an IEEE standard inspired from the earlier Cisco proprietary Multi-Instance Spanning Tree Protocol (MISTP) implementation. MST maps multiple VLANs that have the same traffic flow requirements into the same spanning-tree instance. The Cisco implementation provides up to 16 instances of RSTP (802.1w). The CPU and memory requirements of this version are less than PVRST+ but more than RSTP.

Per VLAN Rapid Spanning Tree Plus(PVRST+)

PVRST+is a Cisco enhancement of RSTP that is similar to PVST+. It provides a separate instance of 802.1w per VLAN. This version addressed both the convergence issues and the suboptimal traffic flow issues. To do this, this version has the largest CPU and memory requirements.

Comparison