Open the lab
[ YOUR LAB FILE ]
Download the starting topology, then work through the lesson in SwitchLab.
- Save the .swlab file without renaming its extension.
- Open SwitchLab. Import and export controls currently require a desktop-width window. On a smaller screen, Tools → Fit brings the topology into view.
- Select Import Sandbox (folder icon), choose the downloaded file, and confirm the device and cable counts below.
- Select a device, then choose Open device on desktop or its name in the bottom bar on smaller screens. Select CLI for switches/routers or Desktop → Terminal for PCs. Enter
enableonly when the prompt ends in >. - Follow this page beside the simulator. Use a free account to export your work. Reimport the original download to restart; export any work you want to keep first.
Prerequisites
- Complete the VLAN Guided Lab and interpret access-port and trunk tables.
- Recognize the difference between a host subnet, an access VLAN and an 802.1Q trunk.
Topology
6 devices · 5 links
Scenario
After an uplink cleanup, students can still communicate across the two closets but staff cannot. Both staff access ports and addresses are correct. Find the inconsistent trunk policy and restore only the required VLAN.
Objectives
- Distinguish a per-VLAN outage from a physical uplink failure.
- Compare both trunk allowed lists and restore the missing VLAN.
- Verify both department paths without allowing unnecessary VLANs.
CCNA blueprint
200-301 v1.1 objectives — this lab covers the following specific skills, not every subtopic in the domain.
- 2.2.a — Verify and repair an interswitch trunk.
- 2.2.b — Distinguish tagged traffic from native VLAN traffic.
Starting information
- Both g0/8 interfaces must carry VLANs 10 and 20. Native VLAN 1 is unchanged; neither trunk should be opened to all VLANs.
- PC1 and PC3 are students; PC2 and PC4 are staff. Keep the addressing and physical cabling shown below.
- No router is present. Inter-department traffic is not a success condition for this Layer 2 repair.
| Host | IPv4 address | Mask | Gateway |
|---|---|---|---|
| PC1 | 192.168.10.10 | 255.255.255.0 | None |
| PC2 | 192.168.20.20 | 255.255.255.0 | None |
| PC3 | 192.168.10.30 | 255.255.255.0 | None |
| PC4 | 192.168.20.40 | 255.255.255.0 | None |
| Device / port | Device / port |
|---|---|
| PC1 / eth0 | SW1 / g0/1 |
| PC2 / eth0 | SW1 / g0/2 |
| SW1 / g0/8 | SW2 / g0/8 |
| PC3 / eth0 | SW2 / g0/1 |
| PC4 / eth0 | SW2 / g0/2 |
Tasks
- Predict whether a total uplink outage would explain the reported symptom. Test the student path and the staff path before changing anything.
- Inspect VLAN membership, both trunk tables and the relevant interface configurations. Record the discrepancy and explain how it prevents the failed path.
- Apply the smallest correction consistent with the approved starting information. Preserve all addresses, cables and working department settings.
- Repeat both directions of staff traffic and both directions of student traffic. Compare the repaired configuration with your diagnosis, then save the switch configuration.
Useful commands
show vlan brief
show interfaces trunk
show running-config
show running-config interface g0/8
copy running-config startup-configProgressive hints
Hint 1
Use the working student path to distinguish an entire uplink outage from a per-VLAN problem.
Hint 2
A VLAN must be allowed at both ends of a trunk. Its presence in show vlan brief does not prove that the trunk carries it.
Hint 3
Compare show interfaces trunk on both switches. Correct SW2’s allowed list to the two VLANs required by the design.
Verification
- Both g0/8 interfaces must carry VLANs 10 and 20. Native VLAN 1 is unchanged; neither trunk should be opened to all VLANs.
- PC1 → 192.168.10.30 and PC3 → 192.168.10.10 succeed.
- PC2 → 192.168.20.40 and PC4 → 192.168.20.20 succeed.
- Inspect the corrected interface configuration; successful pings must not come from flattening the VLAN design.
Solution / walkthrough
Show Solution
Use enable only from a > prompt; if already at #, begin with configure terminal.
SW2
Apply the approved trunk policy on SW2. The student path provides a control before and after the repair; verify the staff path separately.
enable
configure terminal
interface g0/8
switchport trunk allowed vlan 10,20
end
copy running-config startup-configRun every verification check above after the changes. A saved configuration alone does not prove packet delivery.