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Different STP flavors solve the same problem – loop prevention – with different trade-offs in convergence, VLAN support, vendor independence and scalability.

Overview table

STP type Standard What it does Where used Why used
PVST Cisco proprietary One STP instance per VLAN Legacy Cisco Load balancing between VLANs
PVST+ Cisco One instance per VLAN + compatible with 802.1D/CST Cisco + 3rd-party switches VLAN-based STP without compatibility issues
Rapid PVST+ Cisco PVST+ + RSTP (802.1W) Modern Cisco networks Fast convergence + per-VLAN control
CST IEEE 802.1Q One STP instance for all VLANs Simple/small networks Low complexity
RSTP IEEE 802.1W Fast STP with sync mechanism Any network Fast convergence
MST IEEE 802.1S Many VLANs per STP instance Large networks Scalability & performance

Fact sheets

STP (802.1D) RSTP (802.1W) PVST PVST+ Rapid PVST+ MST (802.1S)
Type IEEE IEEE Cisco (ISL trunk) Cisco (802.1Q) Cisco (802.1W engine) IEEE (now part of 802.1Q)
Instances 1 (no VLAN awareness) 1 (no VLAN awareness) 1 per VLAN 1 per VLAN, interoperates with CST 1 per VLAN 1 IST + up to 15 MSTIs, region-based, VLAN mapping
Port roles Root, Designated, Non-Designated Root, Designated, Alternate, Backup Root, Designated, Non-Designated Root, Designated, Non-Designated Root, Designated, Alternate, Backup Root, Designated, Alternate, Backup
Port states Blocking, Listening, Learning, Forwarding Discarding, Learning, Forwarding Blocking, Listening, Learning, Forwarding Blocking, Listening, Learning, Forwarding Discarding, Learning, Forwarding Discarding, Learning, Forwarding
Timers Hello 2s, Max Age 20s, FWD 15+15s Hello 2s, dead 3×Hello Same as STP Same as STP Hello 2s, dead 3×Hello Hello 2s, dead 3×Hello
Convergence ~50 s < 1–3 s ~50 s ~50 s < 1–3 s < 1–3 s
Load balancing ❌ ❌ ✅ per VLAN ✅ per VLAN ✅ per VLAN ✅ per instance

Exam memory hook

PVST = per VLAN, MST = VLAN groups

Pitfalls ⚠️

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