Spanning Tree Protocol (STP) Standards

Spanning Tree Protocol (STP) is a networking protocol that is used to prevent loops in a network by creating a logical topology that has only one path between any two devices. STP is implemented using bridges, which are devices that forward or filter Ethernet frames based on the MAC address of the frames. There are several different standards for STP, each with its own specific features and capabilities.

IEEE 802.1d

IEEE 802.1d is the original standard for STP. It was developed in the 1980s and is still widely used today. 802.1d STP uses a timer-based algorithm to determine the best path through the network and to prevent loops. It defines five different link states for a bridge: blocking, listening, learning, forwarding, and disabled. IEEE 802.1d is a standard that defines the operation of media access control (MAC) bridges, which are devices that forward or filter Ethernet frames based on the MAC address of the frames. 802.1d specifies the operation of a spanning tree protocol (STP), which allows multiple bridges to work together to create a loop-free logical topology in a network. The 802.1d standard defines five different link states for a bridge:

Blocking: In the blocking state, a bridge does not forward any frames, but it does listen for BPDUs (Bridge Protocol Data Units) and updates its forwarding database (FDB) with the information it receives. The blocking state is used to prevent loops in the network while the spanning tree is being established.

Listening: In the listening state, a bridge still does not forward any frames, but it prepares to start forwarding frames by updating its FDB and clearing any outdated information. The listening state is used to ensure that the bridge has a consistent and accurate view of the network before it begins forwarding frames.

Learning: In the learning state, a bridge updates its FDB with the source MAC addresses of the frames it receives, but it does not forward any frames. The learning state is used to build a complete and accurate FDB before the bridge begins forwarding frames.

Forwarding: In the forwarding state, a bridge forwards frames based on the information in its FDB. The forwarding state is used to allow normal traffic to pass through the bridge.

Disabled: In the disabled state, a bridge does not forward any frames and does not update its FDB. The disabled state is typically used when a bridge has failed or is being taken offline for maintenance.

By using these different link states, 802.1d STP allows multiple bridges to work together to create a loop-free logical topology in a network, which helps to prevent network issues caused by loops and ensures that data is delivered reliably.

IEEE 802.1w

IEEE 802.1w, also known as Rapid STP (RSTP), is an updated version of 802.1d STP that was developed to converge faster after a topology change. RSTP uses a handshake-based algorithm to determine the best path through the network and to prevent loops. It defines three different link states for a bridge: discarding, learning, and forwarding.

IEEE 802.1s

IEEE 802.1s, also known as Multiple STP (MSTP), is a version of STP that allows a single network to be partitioned into multiple STP domains, or MSTIs (MST Instances). This can be useful in large networks where multiple VLANs need to be isolated from each other. MSTP uses a combination of 802.1d and 802.1w algorithms to determine the best path through the network and to prevent loops. It defines three different link states for a bridge: discarding, learning, and forwarding.

Differences Between the STP Standards

Here are some of the key differences between the different STP standards:

• Convergence Time: 802.1d STP has a slower convergence time than 802.1w and 802.1s, which means it takes longer to recover from a topology change. 802.1w and 802.1s have faster convergence times because they use more advanced algorithms to determine the best path through the network.
• Number of Link States: 802.1d STP has five different link states (blocking, listening, learning, forwarding, and disabled), while 802.1w and 802.1s have only three (discarding, learning, and forwarding).
• Number of STP Domains: 802.1d and 802.1w support only a single STP domain, while 802.1s allows a network to be partitioned into multiple STP domains (MSTIs).

Conclusion

In conclusion, STP is a critical protocol for ensuring the reliable operation of a network. By understanding the different STP standards and how they differ, you can choose the best one for your specific needs and ensure that your network is configured optimally for reliable data delivery.