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
- Read interface status, routing tables, and IOS running configuration.
- Understand OSPF process IDs, router IDs, area 0, and passive interfaces.
- Complete the static routing lab or demonstrate equivalent routing knowledge.
Topology
4 devices · 3 links
Scenario
The branch reports an outage after a configuration cleanup. The operations dashboard still shows a FULL OSPF neighbor, so the uplink initially looks healthy. Inspect the actual LAN prefixes to find a removed advertisement and repair the routing policy without restarting the working neighbor relationship.
Objectives
- Use a healthy neighbor as evidence without mistaking it for complete reachability.
- Identify which router is responsible for originating a missing LAN prefix.
- Restore the omitted LAN advertisement and verify the return path.
CCNA blueprint
200-301 v1.1 objectives — this lab covers the following specific skills, not every subtopic in the domain.
- 3.4.a — Troubleshoot single-area OSPFv2 neighbor adjacency.
- 3.4.d — Identify peers by router ID.
- 3.1.a — Distinguish OSPF-learned routes from connected routes.
Starting information
- Both routers have a working area-0 transit adjacency. R1’s LAN is still advertised.
- R2’s 10.20.20.0/24 LAN must be advertised in area 0 while its g0/0 remains passive.
- A single missing network statement causes the incident. Do not change addressing, router IDs, passive settings or the transit network.
| Host | IPv4 address | Mask | Gateway |
|---|---|---|---|
| PC1 | 10.10.10.10 | 255.255.255.0 | 10.10.10.1 |
| PC2 | 10.20.20.20 | 255.255.255.0 | 10.20.20.1 |
| Router | Interface | IPv4 address | Mask |
|---|---|---|---|
| R1 | g0/0 | 10.10.10.1 | 255.255.255.0 |
| R1 | g0/1 | 10.0.12.1 | 255.255.255.252 |
| R2 | g0/0 | 10.20.20.1 | 255.255.255.0 |
| R2 | g0/1 | 10.0.12.2 | 255.255.255.252 |
| Device / port | Device / port |
|---|---|
| PC1 / eth0 | R1 / g0/0 |
| R1 / g0/1 | R2 / g0/1 |
| PC2 / eth0 | R2 / g0/0 |
Tasks
- Confirm FULL neighbors on both sides and compare the remote LAN entries. Record why the presence of a route on only one router is insufficient.
- Inspect R2’s interface address and OSPF network statements. Identify which statement should select its LAN interface.
- Restore only the omitted /24 statement in area 0. Keep the LAN passive.
- Check both routing tables and both workstation directions. Explain why removing passive-interface g0/0 was not necessary.
Useful commands
show ip interface brief
show ip ospf neighbor
show ip ospf interface brief
show ip route
show running-config
copy running-config startup-configProgressive hints
Hint 1
Look for the specific destination prefix in the routing table. The neighbor table does not list which LANs are being advertised.
Hint 2
The router directly attached to a LAN must include that interface in OSPF for this design. Trace the missing prefix back to its owner.
Hint 3
R2 needs a network statement matching 10.20.20.1 with the /24 wildcard. Add it to process 1, area 0, while retaining passive g0/0.
Verification
- Neighbors stay FULL throughout the repair. Initially R2 knows the HQ LAN, but R1 does not know the branch LAN.
- R2’s running configuration contains network 10.20.20.0 0.0.0.255 area 0 and passive-interface g0/0.
- R1 learns O 10.20.20.0/24 via 10.0.12.2; R2 retains O 10.10.10.0/24 via 10.0.12.1.
- Both workstation ping directions succeed after the missing advertisement is restored.
Solution / walkthrough
Show Solution
Use enable only from a > prompt; if already at #, begin with configure terminal.
R2
Restore participation of the connected branch LAN. Passive operation is appropriate on a workstation LAN and does not prevent its OSPF advertisement.
enable
configure terminal
router ospf 1
network 10.20.20.0 0.0.0.255 area 0
end
copy running-config startup-configRun every verification check above after the changes. A saved configuration alone does not prove packet delivery.