STP vs RSTP vs MST: Full Comparison with Real Labs & CLI [2025] [CCNP ENTERPRISE]

If you’ve ever sat in front of your topology wondering “Why is one link blocking? Why did convergence take so long?”, you’ve already met the mysterious world of Spanning Tree Protocols. STP, RSTP, and MST sound intimidating at first—but once you get hands-on and understand how they operate, it all clicks. In this post, I’ll break it down like we do in our labs—clear, visual, and step-by-step—so you’re not just memorizing, but truly mastering these critical Layer 2 protocols.

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Theory in Brief – STP vs RSTP vs MST

Spanning Tree Protocol (STP) was created to prevent loops in a Layer 2 network by blocking redundant paths. It ensures only one active path exists between switches by forming a tree-like structure and disabling (blocking) unnecessary links.

Then came Rapid Spanning Tree Protocol (RSTP), which improved upon STP with faster convergence times. It replaced STP’s long transition timers (up to 50 seconds!) with quicker state changes, making it better suited for modern networks.

Multiple Spanning Tree (MST) took it one step further—allowing multiple VLANs to be grouped into a single spanning-tree instance. This is ideal in large-scale enterprise networks where running a separate instance of STP per VLAN (like in PVST+) becomes inefficient.

The protocols differ in convergence time, compatibility, scalability, and VLAN handling. But understanding where to use each—and how to configure and troubleshoot them—is what this article is all about.

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Summary – Comparison & Pros/Cons

Feature/Aspect	STP (802.1D)	RSTP (802.1w)	MST (802.1s)
Convergence Time	30–50 seconds	1–6 seconds	1–6 seconds
Port States	5 (Blocking, Listening, Learning, Forwarding, Disabled)	3 (Discarding, Learning, Forwarding)	Same as RSTP
VLAN Support	PVST+ (1 per VLAN)	Rapid PVST+ (1 per VLAN)	Multiple VLANs per instance
Resource Efficiency	Low (1 STP per VLAN)	Low	High
Backward Compatibility	Yes	Yes	Yes (requires config)
Scalability	Limited	Limited	High (with instances)
Best Use Case	Legacy systems	Medium-sized networks	Enterprise & data centers
Cisco Default (modern)	PVST+	Rapid PVST+	MST

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Essential CLI Commands (Cisco IOS)

Task	Command	Description
View spanning-tree status	show spanning-tree	Displays STP, RSTP, MST status
Enable RSTP	spanning-tree mode rapid-pvst	Enables Rapid PVST+
Enable MST	spanning-tree mode mst	Switch to MST mode
Configure MST region	spanning-tree mst configuration	Enters MST config mode
Assign VLANs to instance in MST	instance 1 vlan 10,20,30	Maps VLANs to instance
Configure root bridge priority	spanning-tree vlan 10 priority 4096	Sets switch as root for VLAN
Show MST instance info	show spanning-tree mst	View MST instances and roles
Show interface STP role/state	show spanning-tree interface <intf>	Shows port status in STP

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Real-World Use Cases

Use Case	Recommended Protocol	Why?
Small office with few VLANs	RSTP (Rapid PVST+)	Fast convergence, simple config
Legacy switch hardware	STP (PVST+)	Maximum compatibility
Large enterprise/data center with many VLANs	MST	Groups VLANs to reduce CPU usage
Multi-VLAN voice/data network	RSTP or MST	Ensures fast failover with VLAN control
Redundant core/distribution switches	MST	Scales better with many VLANs

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EVE-NG LAB – Simulating STP, RSTP, and MST

Objective:

• Compare how each spanning tree protocol behaves in link failure.
• Simulate convergence delay between STP, RSTP, and MST.

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Topology

VLAN 10 is configured across all switches with different STP modes.

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STP Configuration (SW1)

spanning-tree mode pvst
vlan 10
 name DATA

spanning-tree vlan 10 priority 4096

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RSTP Configuration (SW2)

spanning-tree mode rapid-pvst
vlan 10
 name DATA

spanning-tree vlan 10 priority 8192

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MST Configuration (SW3)

spanning-tree mode mst
spanning-tree mst configuration
 name NETJOURNEY
 revision 1
 instance 1 vlan 10
 exit

spanning-tree mst 1 priority 12288

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Lab Tests

1. Disable root link and measure reconvergence time using ping and show spanning-tree.
2. Observe how STP takes ~30 seconds, while RSTP and MST converge in ~1-2 seconds.

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Troubleshooting Tips

Symptom	Likely Cause	Recommended Command / Fix
Slow convergence after failure	STP in use instead of RSTP/MST	Switch to RSTP or MST
VLANs not participating in MST	Not assigned to any instance	spanning-tree mst config
Unexpected root bridge election	Priority too high	Lower root priority
Ports stuck in blocking state	Misconfigured port role	show spanning-tree
No STP seen on ports	Disabled protocol or mismatched config	debug spanning-tree events

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Frequently Asked Questions (FAQ)

1. What is the key difference between STP, RSTP, and MST?

Answer:

Protocol	Full Form	Purpose
STP	Spanning Tree Protocol	Original version for loop prevention
RSTP	Rapid Spanning Tree Protocol	Faster convergence (IEEE 802.1w)
MST	Multiple Spanning Tree	Groups VLANs into STP instances (802.1s)

STP is slow to converge (~30–50 sec), RSTP converges in ~1–2 sec, and MST allows scalability by reducing the number of STP instances.

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2. Which Spanning Tree version is enabled by default on Cisco switches?

Answer:
On modern Cisco switches, the default is typically:

• PVST+ or Rapid PVST+ depending on the IOS version.
  Use the command:

show spanning-tree summary

To verify the active STP mode.

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3. How does RSTP achieve faster convergence than STP?

Answer:
RSTP introduces the concepts of:

• Edge Ports (replaces PortFast)
• Proposal and Agreement (faster negotiation)
• Immediate transition of designated and edge ports to forwarding
  These enhancements reduce the listening and learning delay, allowing near-instant failover in topologies.

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4. What is MST and how is it different from RSTP and PVST+?

Answer:
MST (Multiple Spanning Tree) allows multiple VLANs to share a single STP instance, improving CPU and memory efficiency.
Key differences:

• MST uses instances instead of per-VLAN spanning trees.
• You map VLANs to instances manually.
• Requires MST region configuration (name, revision number, VLAN mapping) to be identical across switches.

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5. Can STP, RSTP, and MST coexist in the same network?

Answer:
Yes, but with care. Cisco supports STP interoperability:

• MST can interoperate with RSTP and PVST+
• MST boundary ports treat non-MST switches as STP-compatible
  Best practice: Plan transitions carefully and configure MST regions correctly to avoid topology instability.

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6. How do I configure MST on a Cisco switch?

Answer:

conf t
spanning-tree mode mst
spanning-tree mst configuration
 name MST_REGION
 revision 1
 instance 1 vlan 10-20
exit
spanning-tree mst instance 1 priority 4096

This creates MST instance 1 for VLANs 10–20. The name, revision, and VLAN mapping must match on all MST region switches.

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7. How do I verify which STP version is running on a switch?

Answer:
Use:

show spanning-tree summary

Look for:

• Spanning tree enabled protocol: This tells you if it’s PVST+, RPVST, or MST.
  You can also run:

show spanning-tree mst configuration

To verify MST-specific settings.

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8. What are the port states in each STP version?

Answer:

Protocol	Port States
STP	Blocking, Listening, Learning, Forwarding, Disabled
RSTP	Discarding, Learning, Forwarding
MST	Same as RSTP (based on IEEE 802.1w)

RSTP and MST use “discarding” instead of blocking/listening, simplifying the state model.

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9. Which STP version should I use in a large enterprise network?

Answer:

• Use MST for scalability if you have many VLANs (reduces overhead)
• Use Rapid PVST+ for simplicity in smaller networks with per-VLAN topology needs
  MST is preferred in data centers and campus core, while RPVST+ is fine at access/distribution layers.

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10. How does MST ensure consistency across the network?

Answer:
MST uses a concept of MST Regions, which require all participating switches to have:

• The same region name
• The same revision number
• The same VLAN-to-instance mapping

If any mismatch occurs, the switch treats the neighbor as outside the region, and forms an MST boundary, potentially increasing convergence time.

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YouTube Link

Watch the Complete CCNP Enterprise: STP vs RSTP vs MST: Full Comparison with Real Labs & CLI Lab Demo & Explanation on our channel:

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Final Note

Understanding how to differentiate and implement STP vs RSTP vs MST: Full Comparison with Real Labs & CLI is critical for anyone pursuing CCNP Enterprise (ENCOR) certification or working in enterprise network roles. Use this guide in your practice labs, real-world projects, and interviews to show a solid grasp of architectural planning and CLI-level configuration skills.

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