All Type of Spanning-Tree Protocols – The Ultimate Guide
STP is used to ensure network availability with redundant paths and no loops. Multiple types of spanning tree protocols have emerged since the introduction of IEEE 802.1D. PVST+ is the default spanning-tree mode for Cisco Catalyst switches, and it is enabled on all switch ports. The various types of spanning-tree protocols include:
What is STP?
The original version of IEEE 802.1D, STP provides redundant network connectivity without a loop. It is called the CST (Common Spanning Tree). It assumes a single instance of spanning tree for the entire bridged network, regardless of the number of VLANs.
There is only one Root Bridge in the entire network, so all traffic flows along the same path. The STP is extremely sluggish and convergence takes a very long time. STP has a convergence time of 32 seconds. 802.1D-2004 is the most recent revision of the standard spanning-tree protocol.
Due to the fact that CST uses a single Root Bridge, its CPU and memory requirements are lower than those of other protocols. Due to the fact that there is only one Root Bridge and one tree, all VLAN traffic flows over the same path, which can result in suboptimal traffic flows.
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Per VLAN Spanning Tree +
PVST+ is an enhanced version of STP that provides a dedicated 802.1D spanning tree Root Bridge for each VLAN on a network. It is the default STP version. PVST+ moves less quickly than Common Spanning Tree (CST). It consumes less bandwidth than CST and optimises network performance more effectively than CST. PVST+ required additional CPU and memory.
Comparable to the original STP, the separate instance and separate Root Bridge support Port Fast, Uplink Fast, Backbone Fast, BPDU filter, BPDU guard, loop guard, and root guard, among other features.
Port roles are identical to those in RSTP. Separate instance and root bridge for each VLAN increases CPU and memory needs. PVST+ enables spanning-tree optimization for each VLAN’s traffic. The convergence of PVST+ is comparable to that of 802.1D. However, it supports per-VLAN convergence.
Rapid Spanning Tree Protocols – RSTP
RSTP is referred to as IEEE 802.1w. This is an advanced version of STP that provides faster convergence than CST while maintaining a single root bridge. RSTP requires more bridge resources than CST but fewer than PVST+. RSTP resolves a number of convergence issues, but it still only offers a single instance of STP and does not address suboptimal traffic flow issues. Due to faster convergence, this version requires more CPU and memory than CST, but less than Rapid PVST+.
Rapid Per VLAN Spanning Tree
Rapid PVST+ is a Spanning Tree standard that provides faster convergence than PVST+ and a separate instance of 802.1w per VLAN, but requires significantly more CPU and memory than alternative STP standards. Port Fast, BPDU guard, BPDU filter, root guard, and loop guard are all supported by the distinct instance. It resolves the issues of convergence and suboptimal traffic flow.
Multiple Spanning Tree Protocols – MSTP
MSTP is the IEEE 802.1s standard that was inspired by Cisco’s proprietary MISTP implementation. It reduces the required number of STP instances by mapping multiple VLANs with identical traffic flow requirements to a single spanning-tree instance.
Multiple Spanning Tree
MST is Cisco’s equivalent to MSTP, offering up to 16 instances of RSTP (802.1w) and combining multiple VLANs with the same physical and logical topology into a single RSTP instance. Each instance of RSTP is compatible with PortFast, BPDU guard, BPDU filter, root guard, and loop guard. This version’s CPU and memory requirements are less than Rapid PVST+ but greater than RSTP.