What are the pros and cons of using different spanning tree protocols for root bridge election?

1 STP (Spanning Tree Protocol)

STP is the original and most basic version of the spanning tree protocol, defined by IEEE 802.1D. It elects the root bridge based on the lowest bridge ID, which is a combination of a priority value and a MAC address. The lower the bridge ID, the higher the chance of becoming the root bridge. The priority value can be manually configured to influence the election. STP has some advantages, such as simplicity, compatibility, and low resource consumption. However, it also has some drawbacks, such as slow convergence, high latency, and limited load balancing. STP can take up to 50 seconds to converge after a topology change, which can cause network disruption and packet loss. STP also blocks all but one path to the root bridge, which can create congestion and waste bandwidth. STP does not support multiple instances or regions, which means it cannot differentiate between different VLANs or traffic types.

2 RSTP (Rapid Spanning Tree Protocol)

RSTP is an enhanced version of STP, defined by IEEE 802.1w. It elects the root bridge using the same criteria as STP, but it improves the convergence time and the utilization of redundant links. RSTP can converge within a few seconds, which reduces the impact of topology changes on network performance. RSTP also introduces the concept of alternate and backup ports, which are ready to take over the role of the designated port in case of a failure. This allows RSTP to use multiple paths to the root bridge, which improves load balancing and fault tolerance. RSTP also supports edge ports, which are directly connected to end devices and can skip the blocking state. RSTP has some benefits, such as fast convergence, better load balancing, and edge port optimization. However, it also has some limitations, such as compatibility issues, complexity, and lack of VLAN awareness. RSTP may not interoperate well with legacy devices that run STP, which can cause inconsistent behavior and loops. RSTP also requires more configuration and monitoring, as it has more port roles and states. RSTP still does not support multiple instances or regions, which means it cannot segregate different VLANs or traffic types.

3 MSTP (Multiple Spanning Tree Protocol)

MSTP is an advanced version of RSTP, defined by IEEE 802.1s. It elects the root bridge using the same criteria as RSTP, but it adds the ability to create multiple spanning tree instances (MSTIs) and regions (MSTRs). MSTIs are logical groups of VLANs that share the same spanning tree topology and root bridge. MSTRs are logical groups of switches that run the same MST configuration and communicate with each other using MST BPDUs. MSTP allows network administrators to map different VLANs to different MSTIs, which can achieve VLAN-specific load balancing and root bridge election. MSTP also allows network administrators to define different MSTRs, which can isolate different parts of the network and reduce the scope of spanning tree calculations. MSTP has some advantages, such as VLAN awareness, scalability, and flexibility. However, it also has some challenges, such as compatibility issues, complexity, and configuration consistency. MSTP may not interoperate well with devices that run STP or RSTP, which can cause inconsistent behavior and loops. MSTP also requires more configuration and verification, as it has more parameters and rules to follow. MSTP also requires that all switches in the same MSTR have the same MST configuration, which can be difficult to maintain and troubleshoot.