[Day 9] 4. Types of STP

Types of STP

1. CST (Common Spanning Tree)

   • A single spanning tree is used for the entire network, regardless of the number of VLANs. All VLANs share the same tree, and any change in the network topology affects all VLANs.

2. PVST (Per VLAN Spanning Tree)

   • This version of STP runs a separate instance of the spanning tree for each VLAN, allowing better optimization of network resources by using different paths for different VLANs.

3. PVST+ (Per VLAN Spanning Tree Plus)

   • An enhancement of PVST, PVST+ allows Cisco devices to support both 802.1Q and ISL (Inter-Switch Link) encapsulation formats. It is compatible with PVST but with additional features and improvements.

4. MST (Multiple Spanning Tree)

   • MST allows the grouping of multiple VLANs into a single spanning tree instance, reducing the number of STP instances and making the network more efficient. Each MST region can have its own set of spanning tree topologies.

5. RSTP (Rapid Spanning Tree Protocol)

   • RSTP is an improvement over the original STP (802.1D) that provides faster convergence times (usually within seconds) by quickly adapting to changes in the network topology.

6. RSTP+

   • This is a Cisco proprietary extension to RSTP, offering even more rapid convergence and additional features for network optimization, specifically in larger and more complex environments.

7. PVRST (Per VLAN Rapid Spanning Tree)

   • PVRST combines the advantages of PVST and RSTP. It runs a rapid spanning tree for each VLAN, offering faster convergence times while still allowing each VLAN to have its own spanning tree.

Difference Between RSTP and CST (Common Spanning Tree)

• RSTP (Rapid Spanning Tree Protocol) can quickly adapt to changes in network topology, typically within seconds (often around 1-3 seconds). It achieves this by utilizing a more efficient method of port state transitions and eliminating the need for timers used in the original STP. This allows for faster recovery from network failures or topology changes.

• CST (Common Spanning Tree), on the other hand, takes longer (often 30 seconds or more) to respond to changes due to the inherent limitations of the traditional STP (802.1D) standard, which relies on slower timers and more complex recalculations when the topology changes.