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CCNA lab 42 of 46

Troubleshooting OSPF adjacencies and routes

Four routers in a ring, four links, and not one healthy OSPF adjacency on the path between the two LANs. Find an area mismatch, a timer mismatch, a passive transit link, a duplicate router ID, an MTU mismatch and a LAN that was never advertised.

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 42 - Troubleshooting OSPF adjacencies and routes

Try it free for 30 minutesRun it on Lite from £3 a day

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Level
Advanced
Time
About 60 minutes
Nodes need
6 vCPU, 6,144 MB
Smallest plan
Lite

The scenario

Overcombe Water's four routers should form one OSPF area 0 ring, so that the office (PC1, behind R1) can reach the telemetry LAN (PC2, behind R4) over either side of the ring. After a weekend of "standardisation" by three different people, PC1 can't reach PC2 at all, and the logs are full of OSPF complaints. There are six faults.

Design: all four routers in area 0; all transit links point-to-point with default timers (hello 10, dead 40) and MTU 1500; LANs advertised but passive; router IDs 1.1.1.1, 2.2.2.2, 3.3.3.3, 4.4.4.4.

LinkAddresses
R1 Gi0/0 – R2 Gi0/010.0.12.1 – .2 /30
R1 Gi0/1 – R3 Gi0/010.0.13.1 – .2 /30
R2 Gi0/1 – R4 Gi0/010.0.24.1 – .2 /30
R3 Gi0/1 – R4 Gi0/110.0.34.1 – .2 /30
R1 Gi0/2 / R4 Gi0/210.42.1.1/24 (PC1 .10) / 10.42.4.1/24 (PC2 .10)

What you’ll practise

  • List everything two OSPF neighbours must agree on
  • Diagnose adjacencies stuck in INIT, EXSTART/EXCHANGE or missing entirely
  • Diagnose duplicate router IDs and passive transit interfaces
  • Diagnose a network that isn't advertised because of a wrong wildcard
  • Fix faults without restarting more than necessary

The tasks

  1. Know what neighbours must agree on
  2. Fix the R1 side
  3. Fix the R2–R4 side
  4. Fix the R3–R4 side
  5. Check what R4 advertises
  6. Fix everything with the least disruption and prove it

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 Troubleshooting OSPF adjacencies and routes6 nodes, 6 links. Every link is listed as text below the diagram.R1R2R3R4PC1PC2Gi0/2eth0Gi0/2eth0Gi0/0Gi0/0Gi0/1Gi0/0Gi0/1Gi0/0Gi0/1Gi0/1
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 R3 Gi0/0
  • R2 Gi0/1 to R4 Gi0/0
  • R3 Gi0/1 to R4 Gi0/1
  • R1 Gi0/2 to PC1 eth0
  • R4 Gi0/2 to PC2 eth0
Nodes in Troubleshooting OSPF adjacencies and routes, 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
R3Cisco IOSvvios-adventerprisek9-m.SPA.159-3.M61 vCPU, 1,024 MB
R4Cisco IOSvvios-adventerprisek9-m.SPA.159-3.M61 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 42 - Troubleshooting OSPF adjacencies and routes 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.