What are the Types of STP?
The Spanning Tree Protocol (STP) standards are a set of network protocols that ensure a loop-free topology for Ethernet networks.
The basic idea behind STP is to prevent network disruptions caused by loops, which are common in Ethernet networks. STP works by organizing the network’s switches into a hierarchy and blocking certain redundant paths to prevent loops. Different versions of STP have been developed over time, including Rapid Spanning Tree Protocol (RSTP) and Multiple Spanning Tree Protocol (MSTP), each offering improvements in speed and efficiency.
These protocols are crucial for maintaining stable and efficient network operations, especially in large or complex network topologies.
These are public or industrial specifications created by the IEEE. Some of these STP types are Cisco proprietary and others are IEEE standards.
You will learn more details on some of these STP variants; below, is a brief description of the key Cisco and IEEE STP variants.
STP: Cisco Proprietary
Per-VLAN Spanning Tree Protocol (PVST) – Maintains a spanning tree instance for each VLAN configured in the network. It uses the Cisco proprietary ISL trunking protocol that allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs.
Because PVST treats each VLAN as a separate network, it can load balance traffic at Layer 2 by forwarding some VLANs on one trunk and other VLANs on another trunk without causing a loop. For PVST, Cisco developed several proprietary extensions to the original IEEE 802.1D STP, such as BackboneFast, UplinkFast, and PortFast.
Per-VLAN Spanning Tree Protocol Plus (PVST+) – Cisco developed PVST+ to provide support for IEEE 802.1Q trunking. PVST+ provides the same functionality as PVST, including the Cisco proprietary STP extensions.
PVST+ is not supported on non-Cisco devices. PVST+ includes the PortFast enhancement called BPDU guard, and root guard.
Rapid Per-VLAN Spanning Tree Protocol (rapid PVST+) – Based on the IEEE 802.1w standard and has a faster convergence than STP (standard 802.1D). Rapid PVST+ includes Cisco-proprietary extensions such as BackboneFast, UplinkFast, and PortFast.
IEEE Standards.
Rapid Spanning Tree Protocol (RSTP) – First introduced in 1982 as an evolution of STP (802.1D standard). It provides faster spanning-tree convergence after a topology change. RSTP implements the Cisco-proprietary STP extensions, BackboneFast, UplinkFast, and PortFast, into the public standard. As of 2004, the IEEE has incorporated RSTP into 802.1D, identifying the specification as IEEE 802.1D-2004. So when you hear STP, think RSTP.
Multiple STP (MSTP) – Enables multiple VLANs to be mapped to the same spanning-tree instance, reducing the number of instances needed to support a large number of VLANs.
MSTP was inspired by the Cisco-proprietary Multiple Instances STP (MISTP) and is an evolution of STP and RSTP. It was introduced in IEEE 802.1s as an amendment to 802.1Q, 1998 edition. Standard IEEE 802.1Q-2003 now includes MSTP. MSTP provides for multiple forwarding paths for data traffic and enables load balancing.
Configuring MSTP
