Lab ID: PTL-0045
Title: Spanning Tree Root and Blocked-Port Investigation
Status: TESTED_PASS (Verified live in Cisco Packet Tracer 9.0.1 via MCP loopback bridge automation)
1. Packet Tracer Topology Construction Manifest#
To construct or manually verify this topology in Cisco Packet Tracer:
Device Inventory#
| Device Role | PT Device Model | Display Name | Modules / Slots |
|---|---|---|---|
| Primary Distribution Switch | Cisco Catalyst 2960-24TT | SW-1 | 24 FastEthernet + 2 GigabitEthernet ports |
| Secondary Distribution Switch | Cisco Catalyst 2960-24TT | SW-2 | 24 FastEthernet + 2 GigabitEthernet ports |
| Access Layer Switch | Cisco Catalyst 2960-24TT | SW-3 | 24 FastEthernet + 2 GigabitEthernet ports |
| Distribution Workstation | PC-PT | PC-1 | FastEthernet0 (192.168.1.10/24) |
| Access Workstation | PC-PT | PC-2 | FastEthernet0 (192.168.1.20/24) |
| Enterprise Application Server | Server-PT | Server-1 | FastEthernet0 (192.168.1.100/24) |
Physical Cabling Matrix#
| Link ID | Source Device | Source Port | Destination Device | Destination Port | Cable Type |
|---|---|---|---|---|---|
| L-01 | SW-1 | GigabitEthernet0/1 | SW-2 | GigabitEthernet0/1 | Copper Crossover |
| L-02 | SW-1 | FastEthernet0/1 | SW-3 | FastEthernet0/1 | Copper Crossover |
| L-03 | SW-2 | FastEthernet0/1 | SW-3 | FastEthernet0/2 | Copper Crossover |
| L-04 | SW-1 | FastEthernet0/10 | PC-1 | FastEthernet0 | Copper Straight-Through |
| L-05 | SW-2 | FastEthernet0/10 | Server-1 | FastEthernet0 | Copper Straight-Through |
| L-06 | SW-3 | FastEthernet0/10 | PC-2 | FastEthernet0 | Copper Straight-Through |
2. Positive Verification Test Matrix#
| Test ID | Objective | Command / Procedure | Expected Result | Pass Criteria |
|---|---|---|---|---|
| POS-01 | Primary Root Bridge Election | SW-1# show spanning-tree vlan 1 |
Displays This bridge is the root with Root ID Priority 4097 (priority 4096 sys-id-ext 1). |
SW-1 elected deterministic primary root |
| POS-02 | Secondary Root Priority | SW-2# show spanning-tree vlan 1 |
Bridge ID Priority displays 8193 (priority 8192 sys-id-ext 1). Root Port is GigabitEthernet0/1 with cost 4. |
SW-2 configured as deterministic secondary root |
| POS-03 | Core Trunk Unblocked | SW-1# show spanning-tree vlan 1SW-2# show spanning-tree vlan 1 |
SW-1 Gi0/1 is Desg FWD (Cost 4). SW-2 Gi0/1 is Root FWD (Cost 4). Neither core port is blocked. |
High-speed distribution transit path fully unblocked |
| POS-04 | Alternate Blocked Port on Access Uplink | SW-3# show spanning-tree vlan 1 |
Fa0/1 is Root FWD (Cost 19). Fa0/2 is Altn BLK (Cost 19). |
Access switch redundant uplink safely breaks the loop |
| POS-05 | Distribution Workstation to Server Reachability | PC-1> ping 192.168.1.100 |
4/4 echo replies received with 0% packet loss across core Gigabit link. | Intra-VLAN traffic across core trunk operational |
| POS-06 | Access Workstation to Server Reachability | PC-2> ping 192.168.1.100 |
4/4 echo replies received with 0% packet loss through active access uplink. | Intra-VLAN traffic from edge access switch operational |
3. Negative & Fault Tolerance Test Matrix#
| Test ID | Fault Scenario | Injection Procedure | Observed Symptom | Recovery Procedure |
|---|---|---|---|---|
| NEG-01 | Starter State: Access Root Inversion | In starter topology, execute show spanning-tree vlan 1 on SW-3. |
SW-3 displays This bridge is the root with Priority 4097. An access switch has usurped the root role. |
Reconfigure SW-1 with spanning-tree vlan 1 priority 4096 and SW-3 with default priority 32768. |
| NEG-02 | Starter State: Core Link Blocked | In starter topology, execute show spanning-tree vlan 1 on SW-1 and SW-2. |
SW-1 Gi0/1 is forced into Altn BLK (Alternate / Blocked) state. High-bandwidth core link is disabled by STP. |
Align bridge priorities across distribution layer to ensure core trunk has lowest root path cost (Cost 4). |
4. Reload and Persistence Verification#
completed.pktreloaded cleanly viaipc.appWindow().fileOpen().- Switches
SW-1,SW-2, andSW-3preserved startup configurations from NVRAM across reload. - Core trunk
Gi0/1verified forwarding,SW-3 Fa0/2verified alternate blocked, and full ping reachability confirmed after reload. - Reopened
starter.pktcleanly and confirmed initial faulted root inversion is intact for learner exercise.