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CCNA lab 7 of 46

Troubleshoot interface and cable faults

A two-site network is down after a weekend of changes. Work up the layers with show interfaces, CDP and the logs to find a shut port, an err-disabled link, a duplex mismatch, a cable in the wrong port and a bad mask, and learn what each counter would tell you on real copper and fibre.

Run this lab

It needs Lite: its 6 nodes are set to 6 vCPU and 6,144 MB in total. That fits the free demo too.

In your workspace: Shared, then CCNA 200-301 guided labs, then 07 - Troubleshoot interface and cable faults

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Level
Intermediate
Time
About 50 minutes
Nodes need
6 vCPU, 6,144 MB
Smallest plan
Lite

The scenario

Monday morning at Tidewater Insurance. Over the weekend a contractor "tidied the cabling" and "standardised the port settings". Now the office PC (PC1) can't reach anything, the link to the branch (R2, with PC2) is dead, and the switches are logging complaints. There are five faults, all at the physical, data-link or addressing level. Find each one with evidence before you fix it.

DeviceInterfaceIntended address / roleConnects to
R1Gi0/110.7.1.1/24, head office gatewayS1 Gi0/0
R1Gi0/010.0.12.1/30R2 Gi0/0
R2Gi0/010.0.12.2/30R1 Gi0/0
R2(the port PC2 is cabled to)10.7.2.1/24, branch gatewayPC2
S1Gi0/2link to S2S2 Gi0/2
S2Gi0/1PC1's portPC1
PC1eth010.7.1.10/24, gateway 10.7.1.1S2 Gi0/1
PC2eth010.7.2.10/24, gateway 10.7.2.1R2

Topology: PC1 — S2 Gi0/1 · S2 Gi0/2 — S1 Gi0/2 · S1 Gi0/0 — R1 Gi0/1 · R1 Gi0/0 — R2 Gi0/0 · R2 — PC2. The canvas shows the real cabling.

What you’ll practise

  • Read interface status, line protocol and the error counters in show interfaces
  • Recognise and recover an err-disabled port
  • Detect a speed and duplex mismatch from CDP messages and interface settings
  • Spot a cable plugged into the wrong port and a wrong subnet mask
  • Explain copper and fibre faults: pinouts, Auto-MDIX, distance, signal levels and cable types

The tasks

  1. Learn to read an interface
  2. Fix the PC's port
  3. Recover the err-disabled link
  4. Find the duplex and speed mismatch
  5. Find the cable in the wrong port
  6. Fix the WAN mask
  7. Prove it end to end and know the real-world causes

The Lab Tasks pane has the scenario, these tasks, the checks to run, hints and the full solution.

Topology and devices

The network as it opens in EVE-NG, drawn from the lab’s own canvas, and the image each node runs.

Topology of Troubleshoot interface and cable faults6 nodes, 5 links. Every link is listed as text below the diagram.R1R2S1S2PC1PC2Gi0/1Gi0/0Gi0/2Gi0/2Gi0/1eth0Gi0/1eth0Gi0/0Gi0/0
6 nodes, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • R1 Gi0/0 to R2 Gi0/0
  • R1 Gi0/1 to S1 Gi0/0
  • S1 Gi0/2 to S2 Gi0/2
  • S2 Gi0/1 to PC1 eth0
  • R2 Gi0/1 to PC2 eth0
Nodes in Troubleshoot interface and cable faults, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
R1Cisco IOSvvios-adventerprisek9-m.SPA.159-3.M61 vCPU, 1,024 MB
R2Cisco IOSvvios-adventerprisek9-m.SPA.159-3.M61 vCPU, 1,024 MB
S1Cisco IOSvL2viosl2-adventerprisek9-m.ssa.high_iron_202009291 vCPU, 1,024 MB
S2Cisco IOSvL2viosl2-adventerprisek9-m.ssa.high_iron_202009291 vCPU, 1,024 MB
PC1VPCS hostBuilt in to EVE-NGCounted as 1 vCPU, 1,024 MB
PC2VPCS hostBuilt in to EVE-NGCounted as 1 vCPU, 1,024 MB

How to open this lab

  1. Sign in to your workspace at lab.cloudlabbox.com.

  2. In File Manager, open Shared, then the folder CCNA 200-301 guided labs.

  3. Open 07 - Troubleshoot interface and cable faults and start its nodes, then open Lab Tasks for the scenario and the steps.

The lab is read-only. You can start the nodes and configure the devices, but changes to the topology can’t be saved. To change it, rebuild it in your own folder.

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CloudLabBox is independent of Cisco. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.