host-A can't reach host-B
Two LANs, one router link between them, and no connectivity. Find the gap and fix it.
Scenario
A small two-site network. host-A sits on R1's LAN, host-B sits on R2's LAN, and the two routers are connected by a point-to-point link. Interfaces are up, and both routers can ping each other across the link, but host-A and host-B cannot reach each other.
You're handed the running configs. Routing was set up in a hurry and something's missing. Get host-A and host-B talking, without changing any IP addressing.
Topology
- host-A
10.0.1.10/24→ gateway R110.0.1.1 - host-B
10.0.2.10/24→ gateway R210.0.2.1 - R1 ↔ R2 link: R1
10.0.12.1/30, R210.0.12.2/30
Your job
Restore end-to-end connectivity between the two hosts.
What "done" looks like
host-A ↔ host-B ping works both directions, and R1's table shows the route to the far LAN.
Teaches: routers don't know about networks they aren't directly connected to or told about, and connectivity needs a working path in both directions.
What gets checked
Your solution is verified against each of these:
- R1 has a route to host-B's LAN, pointing across the link to R2
- Ping from host-A (10.0.1.10) to host-B (10.0.2.10) succeeds
- Ping from host-B back to host-A succeeds
Solve it in the browser lab
No setup, no install. Open a live lab: configure each device in the editor or its Cisco IOS terminal, run show/ping/traceroute (or test from the hosts), and watch the network react. The in-house engine grades your fix instantly and issues your proof the moment every check passes.
Open the lab →Prefer your own lab?
- Build the fix locally. New to the tooling? See setting up your lab.
- Push your topology file, device configs, and any playbooks to a public repo (GitHub or GitLab).
- Submit the repo link. We review it by hand, confirm it works, and issue your proof page.