Lab ID: PTL-0044
Title: VLAN Trunk Allowed-List Troubleshooting
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 |
|---|---|---|---|
| Distribution Switch 1 | Cisco Catalyst 2960-24TT | SW-1 | 24 FastEthernet + 2 GigabitEthernet ports |
| Distribution Switch 2 | Cisco Catalyst 2960-24TT | SW-2 | 24 FastEthernet + 2 GigabitEthernet ports |
| Engineering Workstation 1 | PC-PT | PC-Eng1 | FastEthernet0 (192.168.10.10/24, VLAN 10) |
| Marketing Workstation 1 | PC-PT | PC-Mkt1 | FastEthernet0 (192.168.20.10/24, VLAN 20) |
| Operations Workstation 1 | PC-PT | PC-Ops1 | FastEthernet0 (192.168.30.10/24, VLAN 30) |
| Engineering Workstation 2 | PC-PT | PC-Eng2 | FastEthernet0 (192.168.10.20/24, VLAN 10) |
| Marketing Workstation 2 | PC-PT | PC-Mkt2 | FastEthernet0 (192.168.20.20/24, VLAN 20) |
| Operations Workstation 2 | PC-PT | PC-Ops2 | FastEthernet0 (192.168.30.20/24, VLAN 30) |
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 | FastEthernet0/10 | PC-Eng1 | FastEthernet0 | Copper Straight-Through |
| L-03 | SW-1 | FastEthernet0/20 | PC-Mkt1 | FastEthernet0 | Copper Straight-Through |
| L-04 | SW-1 | FastEthernet0/15 | PC-Ops1 | FastEthernet0 | Copper Straight-Through |
| L-05 | SW-2 | FastEthernet0/10 | PC-Eng2 | FastEthernet0 | Copper Straight-Through |
| L-06 | SW-2 | FastEthernet0/20 | PC-Mkt2 | FastEthernet0 | Copper Straight-Through |
| L-07 | SW-2 | FastEthernet0/15 | PC-Ops2 | FastEthernet0 | Copper Straight-Through |
2. Positive Verification Test Matrix#
| Test ID | Objective | Command / Procedure | Expected Result | Pass Criteria |
|---|---|---|---|---|
| POS-01 | Inter-Switch Trunk Operational Mode | SW-1# show interfaces GigabitEthernet0/1 switchportSW-2# show interfaces GigabitEthernet0/1 switchport |
Both switches display Administrative Mode: trunk and Operational Mode: trunk. Negotiation of Trunking is Off. |
Trunk link statically established and operational |
| POS-02 | Native VLAN Alignment | SW-1# show interfaces trunkSW-2# show interfaces trunk |
Both switches show Native VLAN 99 on GigabitEthernet0/1. |
Native VLANs match; no VLAN leakage or CDP mismatch warnings |
| POS-03 | Allowed VLAN List Consistency | SW-1# show interfaces trunkSW-2# show interfaces trunk |
Both switches show 10,20,30,99 under Vlans allowed on trunk. |
All intended corporate VLANs allowed across trunk |
| POS-04 | VLAN 10 (Engineering) Reachability | PC-Eng1> ping 192.168.10.20 |
4/4 echo replies received with 0% packet loss. | Intra-VLAN 10 communication functioning across trunk |
| POS-05 | VLAN 20 (Marketing) Reachability | PC-Mkt1> ping 192.168.20.20 |
4/4 echo replies received with 0% packet loss. | Intra-VLAN 20 communication functioning across trunk |
| POS-06 | VLAN 30 (Operations) Reachability | PC-Ops1> ping 192.168.30.20 |
4/4 echo replies received with 0% packet loss. | Intra-VLAN 30 communication restored across trunk |
| POS-07 | Layer 2 Inter-VLAN Isolation | PC-Eng1> ping 192.168.20.10 |
Request timed out (100% loss). | Proper Layer 2 broadcast domain segmentation maintained |
3. Negative & Fault Tolerance Test Matrix#
| Test ID | Fault Scenario | Injection Procedure | Observed Symptom | Recovery Procedure |
|---|---|---|---|---|
| NEG-01 | Starter State: Pruned VLAN 30 | In starter topology, test ping from PC-Ops1 to PC-Ops2 (ping 192.168.30.20). |
Returns Request timed out (100% loss). VLAN 30 frames are pruned at SW-1's trunk port. |
Execute interface GigabitEthernet0/1 and switchport trunk allowed vlan add 30 on SW-1. |
| NEG-02 | Starter State Fault Identification | On SW-1 and SW-2, run show interfaces trunk and show interfaces switchport. |
SW-1 allows only 10,20,99 (VLAN 30 omitted). SW-2 trunk is configured with Native VLAN 1 instead of 99. |
Align Native VLAN on SW-2 with switchport trunk native vlan 99 and add VLAN 30 to SW-1 trunk allowed list. |
4. Reload and Persistence Verification#
completed.pktreloaded cleanly viaipc.appWindow().fileOpen().- Switches
SW-1andSW-2preserved startup configurations from NVRAM across reload. - Full intra-VLAN reachability across all three VLANs confirmed after reload.
- Reopened
starter.pktcleanly and confirmed initial faulted state is intact for learner exercise.