STP - Spanning Tree Protocol

What is STP?

STP (Spanning Tree Protocol) is a network protocol used to prevent loops in Ethernet networks. It ensures a loop-free topology by selectively blocking redundant paths.

Why is STP useful?

Automatically detects loops
Disables redundant paths
Re-enables them if the active path fails

How it works

Root Bridge Election – Switches elect one switch as the Root Bridge (lowest Bridge ID)
Path Cost Calculation – Each switch finds the shortest path to the Root Bridge
Loop Prevention – STP blocks extra paths to prevent loops
Failure Recovery – If a path fails, STP activates a backup

Where is STP used?

Enterprise LANs with multiple switches
Data centers with redundant links
Campus networks
Any Ethernet-based network with loop potential

Which OSI layer does this protocol belong to?

Layer 2 – Data Link Layer
Operates using MAC addresses
No dependence on IP addresses
Manages switch-to-switch behavior

What are common types of STP?

STP (802.1D) – Original standard
RSTP (802.1w) – Rapid STP for faster convergence
MSTP (802.1s) – Supports multiple spanning trees for VLANs

What are the port roles in STP?

Root Port (RP) – Best path to the Root Bridge (one per switch)
Designated Port (DP) – Forwards frames on a segment
Blocked Port – Does not forward traffic (backup path)
Disabled Port – Shut down or not participating

What are the STP port states?

Blocking – Listens for BPDUs only
Listening – Prepares for data forwarding
Learning – Learns MACs but does not forward
Forwarding – Active traffic forwarding
Disabled – Manually turned off

What is a BPDU?

A Bridge Protocol Data Unit (BPDU) is a special message used by STP to share topology information between switches.

What happens during a topology change?

A switch detects a change (e.g., link down/up)
It sends a Topology Change Notification (TCN) BPDU
The Root Bridge updates the topology
Switches flush MAC tables and reconverge

What is the working flow of STP?

All Switches Send BPDUs – Each switch assumes it’s the Root and sends its Bridge ID (priority + MAC) with path cost = 0
Elect the Root Bridge – Lowest Bridge ID wins – Other switches become non-root
Calculate Path Cost to Root
- Cost based on link speed:
- 10 Mbps = 100
- 100 Mbps = 19
- 1 Gbps = 4
- 0 Gbps = 2
Assign Port Roles * Based on best paths and BPDUs: * Root Port * Designated Port * Blocked Port
Block Redundant Links – Only Root & Designated Ports forward – Blocked ports prevent loops
Transition Port States (802.1D) – Blocking → Listening → Learning → Forwarding – Takes 30–50 seconds to converge
Handle Topology Changes – Affected switch sends TCN BPDU – MAC tables are flushed – Tree recalculates and stabilizes

What are the real-time applications of STP?

VoIP (Voice over IP)
Video Conferencing (e.g., Zoom, Microsoft Teams)
Industrial Automation
IPTV / Live Video Streaming

Learnings in this section

In this section, you are going to learn

Terminology

Terminology

Version Info

Version Info

STP Version&IEEE Details

S.No	Version	IEEE	Year	contribution/core ideas
1	STP (CST)	IEEE 802.1D	1990	Original version; prevents loops in Layer 2 networks using a single spanning tree.
2	RSTP	IEEE 802.1w	2001	Rapid Spanning Tree Protocol; faster convergence than STP.
3	MSTP	IEEE 802.1s	2002	Multiple Spanning Tree Protocol; maps multiple VLANs to a few spanning tree instances.
4	PVST+	Cisco proprietary		Per-VLAN STP; runs a separate STP instance per VLAN.
5	Rapid PVST+	Cisco proprietary		Ciscos enhancement of RSTP with per-VLAN support.
6	MST (Cisco MSTP)	Cisco implementation of IEEE 802.1s		Supports up to 16 RSTP instances mapped to VLANs.

STP Basic Setup on Ubuntu using IPv4

setup

STP Basic Setup on Ubuntu using IPv6

setup

STP Protocol Packet Details

STP CONFIGURATION BPDU Packet

S.No	packet details	Description	Size (Bytes)
1	Configuration BPDU	It contains information about the root bridge, path cost, timers, and is used to maintain and calculate the spanning tree topology.	35 Bytes
	Protocol Identifier	Identifies the protocol as STP (usually 0x0000)	2
	Protocol Version	Version of STP (0 for IEEE 802.1D)	1
	BPDU Type	Type of BPDU (0x00 = Configuration)	1
	BPDU Flags	TC and TCA flags	1
	Root Bridge ID	Priority (2 bytes) + MAC (6 bytes)	8
	Root Path Cost	Cost to reach the root bridge	4
	Sender Bridge ID	Priority (2 bytes) + MAC (6 bytes)	8
	Port Identifier	ID of the port sending the BPDU	2
	Message Age	Time since the root sent the configuration message	2
	Max Age	Maximum age before the BPDU is discarded	2
	Hello Time	Time interval between BPDUs sent by the root bridge	2
	Forward Delay	Time spent in listening and learning states	2

STP TOPOLOGY CHANGE NOTIFICATION Packet

Topology Change Notification	Sent by a bridge when it detects a topology change. It notifies the root bridge to initiate a topology change process.	4 Bytes
Protocol Identifier	Identifies the protocol as STP (usually 0x0000)	2
Protocol Version	Version of STP (0 for IEEE 802.1D)	1
BPDU Type	Type of BPDU (0x80 = TCN)	1

STP Usecases

S.No	Use Case	Description
1	Loop Prevention in LANs	Prevents broadcast storms and data duplication by blocking redundant paths in Ethernet networks.
2	Redundant Link Management	Allows multiple physical links between switches for redundancy without causing loops.
3	Automatic Failover	If the active path fails, STP reactivates a previously blocked path to maintain connectivity.
4	Network Topology Stability	Maintains a stable and loop-free topology even when switches or links are added or removed.
5	Data Center Networking	Used in data centers to manage complex switch topologies with multiple redundant paths.
6	Campus and Enterprise Networks	Ensures reliable communication across large networks with many interconnected switches.
7	Bridge and Switch Interconnection	Helps manage traffic between multiple bridges/switches in a scalable way.
8	Minimizing Downtime	Reduces manual intervention during link failures by dynamically recalculating paths.

STP Basic Features

S.No	STP features	Description
1	Loop Prevention	Prevents network loops by blocking redundant paths in a switched network.
2	Redundancy Support	Allows multiple physical links for backup without causing loops.
3	Automatic Topology Change Handling	Automatically recalculates paths when a switch or link fails.
4	Bridge Election	Elects a Root Bridge to serve as the central point of the network.
5	Port Roles Assignment	Assigns roles like Root Port, Designated Port, and Blocked Port to manage traffic flow.
6	Path Cost Calculation	Uses path cost to determine the shortest and most efficient route to the Root Bridge.
7	Timer-Based Operation	Uses timers like Hello Time, Max Age, and Forward Delay to manage state transitions.
8	Dynamic Reconfiguration	Adapts to changes in the network without manual intervention.
9	Standardized Protocol	Defined by IEEE 802.1D, ensuring compatibility across vendors.
10	Layer 2 Operation	Operates at the Data Link Layer (Layer 2) of the OSI model.

STP Feature : Loop Prevention

Loop Prevention - Testcases

S.No	Test Case	Description	Expected Result
1	STP Initialization	Start STP on all switches	STP begins topology calculation
2	Root Bridge Election	Elect root bridge	Lowest bridge ID becomes root
3	Loop Detection	Create physical loop	STP blocks redundant path
4	Port Blocking	Verify blocked port	One port is placed in blocking state
5	Port Forwarding	Verify forwarding port	Only one path is active
6	Port Listening State	Check transition to listening	Port enters listening before learning
7	Port Learning State	Check transition to learning	Port learns MAC addresses
8	Port Forwarding State	Check transition to forwarding	Port forwards frames
9	BPDU Transmission	Send BPDUs between switches	BPDUs are exchanged correctly
10	BPDU Reception	Receive BPDUs	Switch updates topology info
11	BPDU Filtering	Filter BPDUs on edge port	BPDUs are blocked
12	BPDU Guard	Enable BPDU Guard	Port is disabled on BPDU receipt
13	BPDU Attack Simulation	Simulate rogue BPDU	STP protects root bridge
14	Topology Change Notification	Trigger topology change	STP recalculates paths
15	Loop Recovery	Remove loop	Blocked port transitions to forwarding
16	Redundant Link Addition	Add redundant link	STP blocks one path
17	Root Bridge Failure	Power off root bridge	New root bridge is elected
18	Port Priority Change	Change port priority	STP recalculates path cost
19	Path Cost Adjustment	Modify path cost	STP selects new best path
20	STP Convergence Time	Measure convergence	Network stabilizes within expected time
21	STP on VLANs	Enable STP per VLAN	Each VLAN has independent topology
22	Rapid STP (RSTP) Test	Use RSTP instead of STP	Faster convergence observed
23	Multiple Root Bridges	Configure multiple root bridges	STP selects one root bridge
24	Loop in Access Layer	Create loop in access layer	STP blocks redundant access port
25	Loop in Distribution Layer	Create loop in distribution layer	STP blocks redundant uplink
26	Loop in Core Layer	Create loop in core layer	STP blocks one core path
27	STP Port Roles	Verify port roles (Root, Designated, etc.)	Roles are assigned correctly
28	STP Timer Configuration	Adjust hello, forward delay timers	STP behavior changes accordingly
29	STP Timer Expiry	Simulate timer expiry	STP recalculates topology
30	STP Disabled	Disable STP on switch	Loop forms and causes broadcast storm
31	STP Enabled	Enable STP on switch	Loop is prevented
32	STP Loop Simulation	Simulate loop in testbed	STP blocks one path
33	STP Loop Detection Tool	Use loop detection tool	Tool confirms STP loop prevention
34	STP with Link Aggregation	Use STP with LACP	STP treats aggregated links correctly
35	STP with Redundant Switches	Add redundant switches	STP blocks unnecessary paths
36	STP with Wireless Bridge	Use STP over wireless bridge	STP blocks redundant wireless path
37	STP with Edge Devices	Connect edge devices	STP does not block edge ports
38	STP with Server Farm	Connect servers with dual NICs	STP blocks one NIC path
39	STP with VoIP Phones	Connect VoIP phones	STP does not interfere with voice traffic
40	STP with IP Cameras	Connect IP cameras	STP prevents loop from camera switches
41	STP with IoT Devices	Connect IoT devices	STP handles low-bandwidth devices
42	STP with Legacy Switches	Use old switches	STP still prevents loops
43	STP with Managed Switches	Use managed switches	STP configuration is supported
44	STP with Unmanaged Switches	Use unmanaged switches	STP may not function properly
45	STP with Cloud Network	Simulate STP in cloud topology	STP prevents virtual loop
46	STP with SDN Controller	Integrate STP with SDN	SDN respects STP decisions
47	STP with Network Emulator	Test STP in emulated environment	Loop prevention is verified
48	STP with Monitoring Tools	Monitor STP status	Loop-free topology is confirmed
49	STP with Logging	Enable STP logs	Loop events are recorded
50	STP Compliance Test	Validate STP against IEEE 802.1D	STP passes compliance checks

STP Feature : Redundancy Support

Redundancy Support - Testcases

S.No	Test Case	Description	Expected Result
1	Verify Primary Node Activation	Ensure primary node is active initially	Primary node is active
2	Verify Secondary Node Standby	Ensure secondary node is in standby mode	Secondary node is in standby
3	Failover Trigger	Simulate primary node failure	Secondary node takes over
4	Failback Trigger	Restore primary node	Primary node resumes control
5	Heartbeat Monitoring	Check heartbeat signal between nodes	Heartbeat is consistent
6	Heartbeat Loss Detection	Simulate heartbeat loss	Failover is triggered
7	Manual Failover	Trigger manual failover	Secondary node becomes active
8	Manual Failback	Trigger manual failback	Primary node becomes active
9	Data Sync Check	Verify data sync between nodes	Data is consistent
10	Data Loss Prevention	Simulate failure during sync	No data loss occurs
11	Load Balancing	Distribute load between nodes	Load is balanced
12	Network Partition	Simulate network split	Redundancy handles partition
13	Node Rejoin	Reconnect failed node	Node rejoins cluster
14	Redundancy Mode Switch	Switch between active-active and active-passive	Mode switches successfully
15	Configuration Sync	Change config on primary	Syncs to secondary
16	Alert on Failover	Check alert system on failover	Alert is generated
17	Alert on Failback	Check alert system on failback	Alert is generated
18	Logging Failover Events	Check logs for failover	Logs are accurate
19	Logging Heartbeat Events	Check logs for heartbeat	Logs are accurate
20	CPU Load During Failover	Monitor CPU during failover	Load remains stable
21	Memory Usage During Sync	Monitor memory during sync	Memory usage is optimal
22	Disk Space Monitoring	Check disk usage on both nodes	Disk usage is within limits
23	Redundancy Disabled Mode	Disable redundancy	System runs in standalone mode
24	Redundancy Enabled Mode	Enable redundancy	Redundancy is active
25	Backup Node Health Check	Monitor backup node health	Node is healthy
26	Primary Node Health Check	Monitor primary node health	Node is healthy
27	Redundancy Status API	Call API for status	Returns correct status
28	Redundancy Status UI	Check UI for status	Displays correct status
29	Redundancy Recovery Time	Measure time to recover	Within acceptable limits
30	Redundancy Timeout Config	Change timeout settings	Takes effect immediately
31	Redundancy Role Swap	Swap roles of nodes	Roles are swapped
32	Redundancy Role Lock	Lock roles to prevent swap	Roles remain fixed
33	Redundancy Role Unlock	Unlock roles	Roles can be swapped
34	Redundancy Under Load	Test failover under high load	System handles it
35	Redundancy During Upgrade	Upgrade one node	Redundancy remains intact
36	Redundancy During Reboot	Reboot one node	Other node takes over
37	Redundancy with Firewall	Enable firewall	Redundancy still works
38	Redundancy with VPN	Enable VPN	Redundancy still works
39	Redundancy with Encryption	Enable data encryption	Redundancy still works
40	Redundancy with Compression	Enable compression	Redundancy still works
41	Redundancy with Logging Off	Disable logging	Redundancy unaffected
42	Redundancy with Logging On	Enable logging	Logs are captured
43	Redundancy with Custom Ports	Use non-default ports	Redundancy works
44	Redundancy with DNS Failover	Use DNS-based failover	Works as expected
45	Redundancy with Load Balancer	Add load balancer	Redundancy integrates
46	Redundancy with Cloud Sync	Sync with cloud	Redundancy supports it
47	Redundancy with Local Backup	Use local backup	Redundancy supports it
48	Redundancy with Scheduled Tasks	Run scheduled tasks	Tasks run on active node
49	Redundancy with Time Sync	Sync time between nodes	Time is consistent
50	Redundancy with Power Failure	Simulate power loss	Secondary takes over

STP Feature : Automatic Topology Change Handling

Automatic Topology Change Handling - Testcases

S.No	Test Case	Description	Expected Result
1	Detect Node Join	Add a new node to the network	Topology updates automatically
2	Detect Node Leave	Remove a node from the network	Topology updates automatically
3	Node Failure Detection	Simulate node crash	Topology reflects node removal
4	Node Recovery Detection	Restart failed node	Node rejoins topology
5	Link Failure Detection	Disconnect a link	Topology updates to reflect change
6	Link Recovery Detection	Reconnect a link	Topology restores original state
7	Dynamic Routing Update	Change network path	Routing table updates automatically
8	Loop Prevention	Introduce loop in topology	System prevents loop formation
9	Redundant Path Handling	Add redundant path	Topology includes backup path
10	Load-Based Topology Change	Simulate high load	Topology adapts to balance load
11	Latency-Based Topology Change	Introduce latency	Topology reroutes traffic
12	Bandwidth-Based Topology Change	Reduce bandwidth	Topology adapts accordingly
13	Topology Snapshot Logging	Log topology changes	Snapshot is recorded
14	Topology Change Alert	Trigger topology change	Alert is generated
15	Topology Change Rollback	Revert to previous topology	Rollback is successful
16	Topology Change Audit Trail	Check audit logs	All changes are logged
17	Topology Change API	Call API to fetch topology	Returns updated topology
18	Topology Change UI	View topology on UI	UI reflects changes
19	Topology Change Under Load	Change topology under load	System remains stable
20	Topology Change During Upgrade	Upgrade node	Topology updates without error
21	Topology Change During Failover	Trigger failover	Topology adapts automatically
22	Topology Change During Maintenance	Put node in maintenance	Topology excludes node
23	Topology Change with Firewall	Enable firewall	Topology adapts correctly
24	Topology Change with VPN	Enable VPN	Topology reflects secure links
25	Topology Change with NAT	Enable NAT	Topology handles address translation
26	Topology Change with DHCP	Enable DHCP	Topology updates with new IPs
27	Topology Change with Static IP	Use static IPs	Topology remains stable
28	Topology Change with DNS	Change DNS entries	Topology updates accordingly
29	Topology Change with IPv6	Use IPv6 addresses	Topology handles IPv6
30	Topology Change with IPv4	Use IPv4 addresses	Topology handles IPv4
31	Topology Change with Mixed IP	Use IPv4 and IPv6	Topology supports dual stack
32	Topology Change with Wireless Node	Add wireless node	Topology includes wireless link
33	Topology Change with Wired Node	Add wired node	Topology includes wired link
34	Topology Change with Mobile Node	Move node location	Topology updates dynamically
35	Topology Change with Cloud Node	Add cloud-based node	Topology includes cloud node
36	Topology Change with Edge Node	Add edge node	Topology includes edge node
37	Topology Change with IoT Device	Add IoT device	Topology includes IoT node
38	Topology Change with Gateway	Add gateway	Topology includes gateway
39	Topology Change with Proxy	Add proxy server	Topology includes proxy
40	Topology Change with Load Balancer	Add load balancer	Topology reflects new path
41	Topology Change with Redundant Gateway	Add redundant gateway	Topology includes both
42	Topology Change with VLAN	Add VLAN	Topology reflects segmentation
43	Topology Change with Subnet	Add subnet	Topology includes subnet
44	Topology Change with Broadcast Domain	Change broadcast domain	Topology adapts
45	Topology Change with Multicast	Enable multicast	Topology supports multicast
46	Topology Change with QoS	Enable QoS	Topology prioritizes traffic
47	Topology Change with ACL	Apply access control list	Topology respects ACL rules
48	Topology Change with Security Policy	Apply policy	Topology enforces policy
49	Topology Change with Monitoring Tool	Integrate monitoring	Tool reflects real-time topology
50	Topology Change with Automation Script	Run script to change topology	Topology updates automatically

STP Feature : Bridge Election

Bridge Election - Testcases

S.No	Test Case	Description	Expected Result
1	Default Bridge Election	Power on all switches with default priority	Switch with lowest MAC becomes root bridge
2	Custom Bridge Priority	Set lowest priority on one switch	That switch becomes root bridge
3	Equal Priority, Lower MAC	Set same priority on all switches	Switch with lowest MAC wins
4	Priority Change After Election	Change priority after election	Re-election occurs
5	MAC Address Conflict	Two switches with same MAC	Election fails or logs error
6	Root Bridge Failure	Power off root bridge	New root bridge is elected
7	Root Bridge Recovery	Restore original root bridge	Re-election may occur
8	Manual Root Bridge Assignment	Manually configure root bridge	Configured switch becomes root
9	Bridge ID Verification	Verify bridge ID format	Correct format: priority + MAC
10	Election Logging	Check logs during election	Election events are logged
11	Election Notification	Check for alerts on election	Notification is generated
12	Election Time Measurement	Measure time taken for election	Within protocol-defined limits
13	Election During Topology Change	Trigger topology change	Election adapts accordingly
14	Election with Redundant Links	Add redundant links	Election still functions
15	Election with Loop Prevention	Create loop	Election prevents loop
16	Election with VLANs	Use multiple VLANs	Separate root bridges per VLAN
17	Election with MSTP	Use Multiple Spanning Tree Protocol	Election per instance
18	Election with RSTP	Use Rapid STP	Faster election process
19	Election with PVST+	Use Per VLAN STP	Election per VLAN
20	Election with STP Disabled	Disable STP	No election occurs
21	Election with STP Enabled	Enable STP	Election occurs
22	Election with PortFast	Enable PortFast	Election unaffected
23	Election with BPDU Guard	Enable BPDU Guard	Unauthorized BPDUs blocked
24	Election with BPDU Filter	Enable BPDU Filter	BPDUs are filtered
25	Election with Root Guard	Enable Root Guard	Prevents unauthorized root
26	Election with TCN	Trigger topology change notification	Election responds correctly
27	Election with Edge Ports	Use edge ports	No impact on election
28	Election with Non-STP Switch	Add unmanaged switch	Election unaffected
29	Election with Loopback	Create loopback	Election handles loop
30	Election with Link Aggregation	Use LAG	Election considers logical link
31	Election with STP Timers	Modify STP timers	Election adapts
32	Election with High Latency	Introduce latency	Election still completes
33	Election with Packet Loss	Simulate BPDU loss	Election retries
34	Election with CPU Load	High CPU on switch	Election completes successfully
35	Election with Memory Pressure	Low memory on switch	Election completes
36	Election with Firmware Upgrade	Upgrade firmware	Election re-triggers if needed
37	Election with Power Cycle	Power cycle switch	Election re-evaluates
38	Election with Port Flap	Flap root port	Election remains stable
39	Election with STP Debugging	Enable debug logs	Election steps visible
40	Election with STP Convergence	Measure convergence time	Within expected range
41	Election with STP Loop Detection	Enable loop detection	Election prevents loop
42	Election with STP Topology View	View topology	Root bridge is correctly shown
43	Election with STP Simulation	Simulate election in lab	Matches expected outcome
44	Election with STP Redundancy	Add redundant root bridge	Backup does not interfere
45	Election with STP Priority Tuning	Tune priorities	Desired root bridge elected
46	Election with STP MAC Spoofing	Spoof MAC address	Election detects anomaly
47	Election with STP VLAN Pruning	Enable VLAN pruning	Election per active VLAN
48	Election with STP Path Cost	Modify path cost	Election considers cost
49	Election with STP Root Path Cost	Verify root path cost	Lowest cost path selected
50	Election with STP Reboot Storm	Reboot multiple switches	Election stabilizes eventually

STP Feature : Port Roles Assignment

Port Roles Assignment - Testcases

S.No	Test Case	Description	Expected Result
1	Assign Root Port	Connect switch to root bridge	Port becomes Root Port
2	Assign Designated Port	Connect to non-root segment	Port becomes Designated Port
3	Assign Blocked Port	Create redundant link	Port becomes Blocked Port
4	Assign Alternate Port	Use RSTP with backup path	Port becomes Alternate Port
5	Assign Backup Port	Use RSTP with backup on shared segment	Port becomes Backup Port
6	Root Port Reassignment	Change root bridge	New port becomes Root Port
7	Designated Port Reassignment	Change topology	New port becomes Designated Port
8	Blocked Port Activation	Remove active link	Blocked port becomes active
9	Port Role on Edge Port	Enable PortFast	Port does not participate in STP
10	Port Role on Trunk Port	Use trunk port	Role assigned based on topology
11	Port Role on Access Port	Use access port	Role assigned based on topology
12	Port Role on VLAN	Assign role per VLAN	Role assigned per VLAN instance
13	Port Role on MSTP	Use MSTP	Role assigned per instance
14	Port Role on PVST+	Use PVST+	Role assigned per VLAN
15	Port Role on RSTP	Use RSTP	Roles include Alternate and Backup
16	Port Role on STP Disabled	Disable STP	No role assigned
17	Port Role on STP Enabled	Enable STP	Role assigned based on topology
18	Port Role Change Logging	Change port role	Event logged
19	Port Role Change Alert	Change port role	Alert generated
20	Port Role Change During Failover	Simulate failover	Roles re-evaluated
21	Port Role Change During Reboot	Reboot switch	Roles reassigned
22	Port Role Change During Upgrade	Upgrade firmware	Roles reassigned
23	Port Role Change During Link Flap	Flap link	Role may change
24	Port Role Change During Load	High traffic	Role remains stable
25	Port Role Change During Loop	Create loop	Role changes to prevent loop
26	Port Role with BPDU Guard	Enable BPDU Guard	Unauthorized port blocked
27	Port Role with Root Guard	Enable Root Guard	Prevents root port assignment
28	Port Role with PortFast	Enable PortFast	Port skips STP states
29	Port Role with STP Timers	Modify timers	Role assignment adapts
30	Port Role with Path Cost	Change path cost	Role assignment changes
31	Port Role with Priority Change	Change bridge priority	Role assignment changes
32	Port Role with MAC Address Change	Change MAC	Role assignment may change
33	Port Role with VLAN Pruning	Enable pruning	Role assigned to active VLANs
34	Port Role with ACL	Apply ACL	Role assignment unaffected
35	Port Role with QoS	Enable QoS	Role assignment unaffected
36	Port Role with Loopback	Create loopback	Role changes to prevent loop
37	Port Role with Redundant Links	Add redundant links	One port blocked
38	Port Role with Link Aggregation	Use LAG	Role assigned to logical group
39	Port Role with Wireless Link	Use wireless bridge	Role assigned normally
40	Port Role with Cloud Node	Connect to cloud node	Role assigned based on topology
41	Port Role with Edge Node	Connect edge node	Role assigned based on topology
42	Port Role with Monitoring Tool	Monitor port roles	Roles visible in tool
43	Port Role with Automation Script	Automate role assignment	Roles assigned correctly
44	Port Role with Manual Override	Manually set role	Override takes effect
45	Port Role with Security Policy	Apply policy	Role assignment respects policy
46	Port Role with Firmware Bug	Simulate bug	Role assignment fails or logs error
47	Port Role with STP Loop Detection	Enable loop detection	Role changes to prevent loop
48	Port Role with STP Convergence	Measure convergence time	Roles assigned within limits
49	Port Role with STP Simulation	Simulate topology	Roles assigned correctly
50	Port Role with STP Topology View	View topology	Roles displayed accurately

STP Feature : Path Cost Calculation

Path Cost Calculation - Testcases

S.No	Test Case	Description	Expected Result
1	Default Path Cost	Use default STP settings	Path cost calculated based on link speed
2	Custom Path Cost	Manually set path cost	Custom cost is applied
3	Path Cost for 10 Mbps	Use 10 Mbps link	Cost = 100
4	Path Cost for 100 Mbps	Use 100 Mbps link	Cost = 19
5	Path Cost for 1 Gbps	Use 1 Gbps link	Cost = 4
6	Path Cost for 10 Gbps	Use 10 Gbps link	Cost = 2
7	Path Cost for 100 Gbps	Use 100 Gbps link	Cost = 1
8	Path Cost for Wireless Link	Use wireless bridge	Cost calculated based on speed
9	Path Cost for Fiber Link	Use fiber optic link	Cost reflects high speed
10	Path Cost for Copper Link	Use copper cable	Cost reflects lower speed
11	Path Cost with VLAN	Calculate cost per VLAN	Cost calculated per VLAN instance
12	Path Cost with MSTP	Use MSTP	Cost calculated per instance
13	Path Cost with PVST+	Use PVST+	Cost calculated per VLAN
14	Path Cost with RSTP	Use RSTP	Cost calculated normally
15	Path Cost with STP Disabled	Disable STP	No cost calculated
16	Path Cost with STP Enabled	Enable STP	Cost calculated
17	Path Cost with Link Aggregation	Use LAG	Cost calculated for logical link
18	Path Cost with Redundant Links	Add redundant links	Lowest cost path selected
19	Path Cost with Loopback	Create loopback	Loop avoided using cost
20	Path Cost with Manual Override	Override cost manually	Manual cost used
21	Path Cost with Port Priority	Change port priority	Cost calculation unaffected
22	Path Cost with PortFast	Enable PortFast	Port excluded from STP
23	Path Cost with Root Guard	Enable Root Guard	Cost calculation unaffected
24	Path Cost with BPDU Guard	Enable BPDU Guard	Cost calculation unaffected
25	Path Cost with ACL	Apply ACL	Cost calculation unaffected
26	Path Cost with QoS	Enable QoS	Cost calculation unaffected
27	Path Cost with VLAN Pruning	Enable pruning	Cost calculated for active VLANs
28	Path Cost with STP Timers	Modify timers	Cost calculation unaffected
29	Path Cost with MAC Address Change	Change MAC	Cost calculation unaffected
30	Path Cost with Firmware Upgrade	Upgrade switch	Cost recalculated if needed
31	Path Cost with Reboot	Reboot switch	Cost recalculated
32	Path Cost with Link Flap	Flap link	Cost recalculated
33	Path Cost with High Latency	Introduce latency	Cost remains based on speed
34	Path Cost with Packet Loss	Simulate loss	Cost calculation unaffected
35	Path Cost with CPU Load	High CPU usage	Cost calculation unaffected
36	Path Cost with Memory Pressure	Low memory	Cost calculation unaffected
37	Path Cost with Monitoring Tool	Monitor cost	Cost visible in tool
38	Path Cost with Automation Script	Automate cost setting	Script sets correct cost
39	Path Cost with Security Policy	Apply policy	Cost calculation respects policy
40	Path Cost with Simulation	Simulate topology	Cost calculated correctly
41	Path Cost with Topology Change	Change topology	Cost recalculated
42	Path Cost with Root Bridge Change	Change root bridge	Cost recalculated
43	Path Cost with Designated Port Change	Change designated port	Cost recalculated
44	Path Cost with Alternate Path	Add alternate path	Lowest cost path selected
45	Path Cost with Backup Path	Add backup path	Backup path has higher cost
46	Path Cost with Edge Node	Connect edge node	Cost calculated normally
47	Path Cost with Cloud Node	Connect cloud node	Cost calculated based on link
48	Path Cost with Wireless Mesh	Use mesh network	Cost calculated per hop
49	Path Cost with VPN Tunnel	Use VPN link	Cost calculated based on tunnel speed
50	Path Cost with Firewall	Enable firewall	Cost calculation unaffected

STP Feature : Timer Based Operation

Timer Based Operation - Testcases

S.No	Test Case	Description	Expected Result
1	Default Hello Time	Use default settings	Hello Time = 2 seconds
2	Default Forward Delay	Use default settings	Forward Delay = 15 seconds
3	Default Max Age	Use default settings	Max Age = 20 seconds
4	Custom Hello Time	Set Hello Time to 5s	Hello messages sent every 5s
5	Custom Forward Delay	Set Forward Delay to 10s	Port transitions faster
6	Custom Max Age	Set Max Age to 30s	Root info retained longer
7	Invalid Hello Time	Set Hello Time > Max Age	Configuration rejected
8	Invalid Forward Delay	Set Forward Delay < Hello Time	Configuration rejected
9	Invalid Max Age	Set Max Age < Hello Time	Configuration rejected
10	Hello Timer Expiry	Wait for Hello interval	BPDU sent
11	Forward Delay Expiry	Wait for delay interval	Port transitions to next state
12	Max Age Expiry	Wait for Max Age	Root info discarded
13	Timer Sync Across VLANs	Use PVST+	Timers applied per VLAN
14	Timer Sync Across Instances	Use MSTP	Timers applied per instance
15	Timer Sync in RSTP	Use RSTP	Timers adjusted automatically
16	Timer Sync in STP	Use classic STP	Timers manually configured
17	Timer Change Logging	Modify timer values	Change logged
18	Timer Change Alert	Modify timer values	Alert generated
19	Timer Change During Failover	Simulate failover	Timers re-evaluated
20	Timer Change During Reboot	Reboot switch	Timers restored
21	Timer Change During Upgrade	Upgrade firmware	Timers preserved
22	Timer Change During Link Flap	Flap link	Timers reset
23	Timer Change During Load	High traffic	Timers remain stable
24	Timer Change During Loop	Create loop	Timers help prevent loop
25	Timer with PortFast	Enable PortFast	Timers bypassed
26	Timer with BPDU Guard	Enable BPDU Guard	Timer operation unaffected
27	Timer with Root Guard	Enable Root Guard	Timer operation unaffected
28	Timer with ACL	Apply ACL	Timer operation unaffected
29	Timer with QoS	Enable QoS	Timer operation unaffected
30	Timer with VLAN Pruning	Enable pruning	Timers apply to active VLANs
31	Timer with MAC Change	Change MAC	Timers re-evaluated
32	Timer with Firmware Bug	Simulate bug	Timer misbehavior logged
33	Timer with Monitoring Tool	Monitor timers	Values visible in tool
34	Timer with Automation Script	Automate timer config	Script sets correct values
35	Timer with Security Policy	Apply policy	Timer values enforced
36	Timer with Simulation	Simulate topology	Timers behave as expected
37	Timer with Topology Change	Change topology	Timers re-triggered
38	Timer with Root Bridge Change	Change root bridge	Timers reset
39	Timer with Designated Port Change	Change designated port	Timers re-evaluated
40	Timer with Alternate Path	Add alternate path	Timers apply to new path
41	Timer with Backup Path	Add backup path	Timers apply to backup
42	Timer with Edge Node	Connect edge node	Timers apply normally
43	Timer with Cloud Node	Connect cloud node	Timers apply normally
44	Timer with Wireless Mesh	Use mesh network	Timers apply per link
45	Timer with VPN Tunnel	Use VPN link	Timers apply based on delay
46	Timer with Firewall	Enable firewall	Timers unaffected
47	Timer with STP Convergence	Measure convergence time	Timers influence convergence
48	Timer with STP Loop Detection	Enable loop detection	Timers help prevent loop
49	Timer with STP Debugging	Enable debug logs	Timer events visible
50	Timer with STP Topology View	View topology	Timer values displayed accurately

STP Feature : Dynamic Reconfiguration

Dynamic Reconfiguration - Testcases

S.No	Test Case	Description	Expected Result
1	Add New Switch	Connect a new switch	STP recalculates topology
2	Remove Existing Switch	Disconnect a switch	STP recalculates topology
3	Change Bridge Priority	Modify bridge priority	Root bridge re-election occurs
4	Change Port Cost	Modify path cost	STP updates port roles
5	Change Hello Time	Modify Hello timer	STP updates BPDU interval
6	Change Forward Delay	Modify Forward Delay	Port transition timing updates
7	Change Max Age	Modify Max Age	BPDU aging behavior updates
8	Enable PortFast	Enable PortFast on edge port	Port bypasses STP states
9	Disable PortFast	Disable PortFast	Port follows STP transitions
10	Enable BPDU Guard	Activate BPDU Guard	Unauthorized BPDUs blocked
11	Disable BPDU Guard	Deactivate BPDU Guard	BPDUs allowed
12	Enable Root Guard	Activate Root Guard	Root bridge protection enabled
13	Disable Root Guard	Deactivate Root Guard	Root bridge protection disabled
14	Enable Loop Guard	Activate Loop Guard	Loop prevention enabled
15	Disable Loop Guard	Deactivate Loop Guard	Loop prevention disabled
16	Change STP Mode	Switch to RSTP or MSTP	STP mode changes dynamically
17	VLAN Addition	Add new VLAN	STP instance created
18	VLAN Removal	Remove VLAN	STP instance removed
19	Link Failure	Disconnect active link	STP recalculates path
20	Link Recovery	Reconnect link	STP reconfigures topology
21	Port Role Change	Change port role manually	STP updates role assignment
22	MAC Address Change	Change switch MAC	STP recalculates bridge ID
23	Firmware Upgrade	Upgrade switch firmware	STP resumes with updated config
24	Switch Reboot	Reboot switch	STP recalculates topology
25	Port Flap	Rapid link up/down	STP stabilizes topology
26	Add Redundant Link	Add backup link	STP blocks one path
27	Remove Redundant Link	Remove backup link	STP unblocks active path
28	Change STP Timers	Modify all timers	STP adapts timing behavior
29	Enable MSTP	Activate MSTP	Multiple instances created
30	Enable PVST+	Activate PVST+	VLAN-specific STP enabled
31	Enable RSTP	Activate RSTP	Fast convergence enabled
32	Disable STP	Turn off STP	No topology recalculation
33	Enable STP	Turn on STP	Topology recalculation begins
34	Add Edge Node	Connect edge device	STP adapts port role
35	Add Core Node	Connect core switch	STP recalculates root bridge
36	Add Wireless Bridge	Connect wireless link	STP recalculates path cost
37	Add Cloud Node	Connect cloud-based switch	STP adapts topology
38	Add VPN Tunnel	Connect via VPN	STP recalculates path cost
39	Add Firewall	Insert firewall in path	STP adapts to new topology
40	Add Load Balancer	Insert load balancer	STP recalculates path
41	Add Proxy Server	Insert proxy	STP adapts to new node
42	Add Monitoring Tool	Integrate monitoring	STP events logged
43	Add Automation Script	Automate config changes	STP adapts dynamically
44	Add ACL	Apply access control	STP adapts port behavior
45	Add QoS Policy	Apply QoS	STP unaffected
46	Add VLAN Pruning	Enable pruning	STP recalculates active paths
47	Add Loopback Interface	Create loopback	STP blocks loop path
48	Add High Latency Link	Connect slow link	STP prefers faster path
49	Add Low Bandwidth Link	Connect low-speed link	STP assigns higher cost
50	Add High-Speed Link	Connect 10G+ link	STP assigns lower cost

STP Feature : Standardized Protocol

Standardized Protocol - Testcases

S.No	Test Case	Description	Expected Result
1	STP Protocol Compliance	Verify STP follows IEEE 802.1D	Protocol behavior matches standard
2	RSTP Protocol Compliance	Verify RSTP follows IEEE 802.1w	Protocol behavior matches standard
3	MSTP Protocol Compliance	Verify MSTP follows IEEE 802.1s	Protocol behavior matches standard
4	PVST+ Compatibility	Use PVST+ on Cisco devices	VLAN-specific STP instances created
5	Protocol Version Detection	Detect STP version on switch	Correct version identified
6	Protocol Negotiation	Connect different STP versions	Compatible protocol selected
7	BPDU Format Validation	Inspect BPDU structure	Matches IEEE standard format
8	BPDU Transmission Interval	Verify Hello Time interval	Matches configured timer
9	BPDU Reception Handling	Receive BPDU from peer	Correctly processed
10	BPDU Filtering	Enable BPDU Filter	BPDUs blocked on configured ports
11	BPDU Guard	Enable BPDU Guard	Unauthorized BPDUs cause port shutdown
12	Root Bridge Election	Verify election logic	Follows standardized rules
13	Port Role Assignment	Verify role logic	Matches STP specification
14	Path Cost Calculation	Verify cost logic	Matches IEEE cost table
15	Timer Configuration	Validate Hello, Max Age, Forward Delay	Matches protocol limits
16	Protocol Interoperability	Connect Cisco and HP switches	STP operates correctly
17	Protocol on VLANs	Use STP per VLAN	VLAN-specific instances created
18	Protocol on Trunk Ports	Use trunk ports	STP operates across VLANs
19	Protocol on Access Ports	Use access ports	STP operates normally
20	Protocol on Edge Ports	Enable PortFast	STP bypasses states
21	Protocol with Loop Prevention	Create loop	STP blocks redundant path
22	Protocol with Redundant Links	Add backup link	STP blocks one path
23	Protocol with Link Aggregation	Use LAG	STP treats as single logical link
24	Protocol with Wireless Links	Use wireless bridge	STP operates normally
25	Protocol with Cloud Nodes	Connect cloud switch	STP operates normally
26	Protocol with VPN Tunnel	Use VPN link	STP operates across tunnel
27	Protocol with Firewall	Insert firewall	STP operates normally
28	Protocol with Load Balancer	Insert load balancer	STP adapts to topology
29	Protocol with Proxy Server	Insert proxy	STP operates normally
30	Protocol with Monitoring Tool	Integrate monitoring	STP events visible
31	Protocol with Automation Script	Automate config	STP adapts dynamically
32	Protocol with ACL	Apply ACL	STP operates normally
33	Protocol with QoS	Enable QoS	STP unaffected
34	Protocol with VLAN Pruning	Enable pruning	STP recalculates active paths
35	Protocol with Loopback Interface	Create loopback	STP blocks loop path
36	Protocol with High Latency Link	Connect slow link	STP prefers faster path
37	Protocol with Low Bandwidth Link	Connect low-speed link	STP assigns higher cost
38	Protocol with High-Speed Link	Connect 10G+ link	STP assigns lower cost
39	Protocol with MAC Spoofing	Spoof MAC address	STP detects anomaly
40	Protocol with Firmware Upgrade	Upgrade switch	STP resumes with updated config
41	Protocol with Reboot	Reboot switch	STP recalculates topology
42	Protocol with Port Flap	Rapid link up/down	STP stabilizes topology
43	Protocol with Topology Change	Change topology	STP recalculates paths
44	Protocol with Root Bridge Change	Change root bridge	STP re-elects root
45	Protocol with Designated Port Change	Change designated port	STP updates roles
46	Protocol with Alternate Path	Add alternate path	STP selects lowest cost
47	Protocol with Backup Path	Add backup path	STP blocks backup
48	Protocol with Edge Node	Connect edge device	STP adapts port role
49	Protocol with Simulation	Simulate STP topology	Behavior matches standard
50	Protocol with Compliance Audit	Run audit tool	STP passes compliance checks

STP Feature : Layer 2 Operation

Layer 2 Operation - Testcases

S.No	Test Case	Description	Expected Result
1	MAC Address Learning	Connect host to switch	MAC address learned on correct port
2	MAC Address Aging	Wait for aging time	MAC entry is removed
3	Frame Forwarding	Send frame between hosts	Frame is forwarded correctly
4	Broadcast Frame Handling	Send broadcast	Frame is flooded to all ports except source
5	Unknown Unicast Handling	Send unknown unicast	Frame is flooded
6	Loop Prevention	Create physical loop	STP blocks redundant path
7	Root Bridge Election	Power on switches	Root bridge elected
8	Port Role Assignment	Observe port roles	Correct roles assigned (Root, Designated, Blocked)
9	BPDU Transmission	Monitor BPDUs	BPDUs sent from root bridge
10	BPDU Reception	Receive BPDUs	Switch processes BPDUs
11	Topology Change Notification	Disconnect link	TCN BPDU generated
12	MAC Table Update on TCN	Trigger topology change	MAC table flushed
13	VLAN Segmentation	Use VLANs	Layer 2 separation maintained
14	Trunk Port Operation	Use trunk port	Frames tagged and forwarded correctly
15	Access Port Operation	Use access port	Frames untagged and forwarded
16	PortFast Behavior	Enable PortFast	Port skips STP states
17	BPDU Guard Behavior	Enable BPDU Guard	Port shuts down on BPDU receipt
18	Root Guard Behavior	Enable Root Guard	Prevents unauthorized root bridge
19	Loop Guard Behavior	Enable Loop Guard	Prevents alternate port from becoming designated
20	STP Convergence Time	Measure convergence	Within expected time
21	MAC Table Consistency	Check MAC table	Entries match active topology
22	MAC Flooding Protection	Send excessive MACs	Switch handles or limits entries
23	STP Mode Change	Switch to RSTP	Layer 2 operation continues
24	MSTP Instance Operation	Use MSTP	Layer 2 separation per instance
25	PVST+ Operation	Use PVST+	VLAN-specific Layer 2 paths
26	MAC Address Filtering	Apply filter	Blocked MACs not learned
27	Port Mirroring	Enable mirroring	Traffic copied to mirror port
28	STP with Link Aggregation	Use LAG	STP treats as single logical link
29	STP with Wireless Bridge	Use wireless link	Layer 2 operation continues
30	STP with VPN Tunnel	Use Layer 2 VPN	STP operates across tunnel
31	STP with Cloud Switch	Connect cloud-managed switch	Layer 2 operation continues
32	STP with Edge Device	Connect IoT device	MAC learned and forwarded
33	STP with Loopback Interface	Create loopback	STP blocks loop
34	STP with VLAN Pruning	Enable pruning	Frames not forwarded to pruned VLANs
35	STP with ACL	Apply Layer 2 ACL	Frames filtered as configured
36	STP with QoS	Enable QoS	Frames prioritized correctly
37	STP with Storm Control	Enable storm control	Broadcast/multicast limited
38	STP with Port Security	Enable port security	MAC violations handled
39	STP with MAC Spoofing	Spoof MAC	STP detects or logs anomaly
40	STP with Firmware Upgrade	Upgrade switch	Layer 2 operation resumes
41	STP with Reboot	Reboot switch	Layer 2 operation restored
42	STP with Port Flap	Flap port	STP recalculates topology
43	STP with High Latency Link	Add slow link	STP assigns higher path cost
44	STP with High-Speed Link	Add 10G+ link	STP assigns lower path cost
45	STP with Monitoring Tool	Monitor Layer 2 traffic	Accurate visibility
46	STP with Automation Script	Automate config	Layer 2 behavior adapts
47	STP with Compliance Audit	Run audit	Layer 2 operation passes checks
48	STP with Simulation	Simulate Layer 2 topology	STP behaves as expected
49	STP with MAC Table Overflow	Exceed MAC table size	Switch handles overflow gracefully
50	STP with Multicast Traffic	Send multicast	Frames forwarded per Layer 2 rules

Reference links

Reference links