What is the Difference between spanning tree versions: MSTP vs RSTP vs STP vs PVST
When it comes to configuring Spanning Tree Protocol (STP) on network devices, there are several options to choose from. The four most common are: Multiple Spanning Tree Protocol (MSTP), Rapid Spanning Tree Protocol (RSTP), STP, and Per-VLAN Spanning Tree Protocol (PVSTP). But what’s the difference between them? Let’s break it down further with this comparison sheet between MSTP vs RSTP vs STP vs PVSTP. Hope you have gone through my previous articles on STP, RSTP, and MSTP, if not then I would recommend reading through those posts to grab a solid understanding of the foundation first.
Difference between MSTP vs RSTP vs STP
The most common types of Spanning Tree Protocol are MSTP, RSTP, STP, and PVSTP. They are all similar in that they prevent loops in a network, but there are some key differences.
STP IEEE 802.1D is the original Spanning Tree Protocol and is not as fast as RSTP, but it is still widely used. PVSTP (per VLAN STP) is a proprietary version of STP that is only compatible with Cisco equipment.
RSTP is a faster version of STP and compatible with all other types. MSTP is the latest, and its primary function is to group VLANs into Instances and is compatible with STP and RSTP. Let us dig deeper.
| STP | RSTP | MSTP | |
|---|---|---|---|
| 1 | Its IEEE standard is 802.1D. | Its IEEE standard is 802.1W. | Its IEEE standard is 802.1S. |
| 2 | IEEE 802.1D is the first child of the STP family. | IEEE 802.1W is the successor and an improved version of STP. | IEEE 802.1S is built on top of RSTP to group VLANs into instances for scalability, ease of management, security, etc. |
| 3 | STP results in slower network convergence and not so robust when compared to RSTP and MSTP. | On the other hand, RSTP significantly accelerates network convergence and is more robust than STP. | RSTP is the underlying protocol for MSTP, and that is why it also provides faster convergence similar to RSTP. But it has more features than RSTP. |
| 4 | Deployment of STP is more straightforward than RSTP and MSTP. | RSTP deployment is easier when compared to MSTP. | MSTP needs a proper understanding of STP and additional MSTP concepts before deployment. Which makes it harder to deploy and the reason sometimes network engineers opt for RSTP instead. |
| 5 | STP has three port functions:- Root Port Designated Port Blocked Port | RSTP utilises four ports:- Root Port Designated Port, Alternate Port Backup Port | MSTP has five-port roles:- Root Port Designated Port Alternate port, Backup Port Master port |
| 6 | STP supports five different port states:- Forwarding Learning Listening Blocking Disabled | RSTP is composed of three-port states:- Forwarding Learning Discarding (It replaces Forwarding, Learning, and Listening for fast convergence.) | Since MSTP is built on top of RSTP, it has the same three port states:- Forwarding Learning Discarding |
| 7 | It lacks all link types. | It supports two types of links: shared links and point-to-point links. | It also has two link types, i.e., Shared link and Point to point link. |
| 8 | STP use only 2 bits from the flag octet: Bit 7: Topology Change Acknowledgment. Bit 0: Topology Change | In RSTP, the following flag bits are used: Bit 0 for TCN Bit 1 for Proposal Bits 2 and 3 for Port role Bit 4 for Learning Bit 5 for forwarding Bit 6 for Agreement Bit 7 for TCN | Same as RSTP. |
| 9 | In STP, the root bridge is the only one that sends BPDUs. Others then transfer BPDUs (Bridge protocol data units). | All bridges in RSTP are capable of forwarding BPDUs. | In MSTP, all bridges can forward BPDUs. |
| 10 | In the Spanning Tree Protocol, when a bridge detects a change in the network, it notifies the root, who then notifies all others via BPDU with the TCA bit set, instructing them to clear their database entries when the "short-timer" (Forward delay) expires. | In RSTP, TC (Topology change) is flooded throughout the network; each bridge generates TC (Topology change) and notifies its neighbors when a topology change occurs, immediately deleting old database entries. | Same as RSTP. |
| 11 | If a non-root bridge does not receive Hello after 10*Hello (advertised from the root), the non-root bridge should begin claiming the root role by generating its own Hello. | On the other hand, RSTP does not act until it receives 3*Hello on a root port (advertised from the root). | Same as RSTP. |
| 12 | STP waits until all TC have reached the root and the short timer (Forward delay) has expired before flashing all root database entries. | RSTP immediately deletes all local databases except for the MAC of the port receiving the topology changes (proposal) | Same as RSTP. |
| 13 | STP is compatible with RSTP and MSTP. But it is always advisable to check with the device vendor before deploying more than one Spanning tree Protocol type in your network. | Rapid Spanning Tree Protocol is backward compatible with STP. | MSTP has CST (Common Spanning Tree) Instance, which is backward compatible with the RSTP and STP. |
| 14 | Load balancing or utilizing multiple physical paths in the network is not possible with STP. All VLANs have to follow the same Spanning Tree path. | Same as STP. | Contrary to STP and RSTP, with MSTP, you can group VLANs into separate MST Instances and can utilize multiple physical paths. |
| 15 | Ports connected to endpoints (laptops, computers, printers, etc.) cannot be configured as an edge port for fast transition. There is no concept of edge ports in STP. | When connected to endpoints while in RSTP, these ports can be configured as edge, ports to allow for rapid changes in the forwarding state. | Boundary ports are ports at the edge of an MST region that are connected to either an STP or RSTP bridge or an endpoint. |
What are PVSTP, PVSTP+, and RPVSTP, and what is the difference between the IEEE versions of STP?
The IEEE Spanning Tree Protocol (STP) was developed to provide a standard way of creating a loop-free topology for Ethernet networks. Before STP was published, many vendors who sold VLAN-capable switches developed versions of STP that were compatible with their products. Cisco also developed proprietary versions of STP called PVSTP, PVSTP+, and RPVSTP.
Per-VLAN Spanning Tree (PVST) is developed by Cisco and uses Cisco’s proprietary ISL (Inter-Switch Link) for VLAN encapsulation, while PVST+ uses 802.1Q for VLAN encapsulation. It is important to note that PVST is obsolete, and PVSTP+ is mainly used on cisco switches.
RPVST is a faster and enhanced form of PVSTP+ and creates a separate spanning tree for each VLAN, similar to PVST.
Conclusion
The differences between MSTP vs RSTP vs STP vs PVSTP can be confusing, but the takeaway is that each represents a slightly different take on managing layer 2 traffic flow in a network. The key is to select the Spanning tree that best meets the requirements of your specific network.
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