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Troubleshooting drills

Nine broken networks. Diagnose from symptoms to root cause, ending with a full outage.

9 challenges · ~8 h · every step earns its own verified proof

0/9 solved
Start: A native VLAN mismatch on the trunk →
  1. A native VLAN mismatch on the trunkmedium~35 min

    A mismatch you'll meet in your first month. Read the symptoms off the trunk.

  2. VLAN 20 can't reach VLAN 10medium~45 min

    Two VLANs, one switch, no traffic. Find the layer where it dies.

  3. The link bundle won't come upmedium~40 min

    The bundle won't bond. Compare both ends the way the protocol does.

  4. The wrong switch is the spanning-tree rootmedium~40 min

    Traffic takes a strange path because an old switch keeps winning the root election.

  5. A remote subnet isn't getting addressesmedium~50 min

    A whole subnet has no addresses. Follow the broadcast that never came back.

  6. The OSPF neighbors won't come upmedium~45 min

    A stuck adjacency. Work the OSPF state machine instead of guessing.

  7. The web app went dark after a changemedium~45 min

    It broke right after a change. Find the line someone added.

  8. BGP won't come up between two ASesmedium~60 min

    The session between ASes won't establish. Read it from both sides.

  9. Everything's down: restore the networkhard~120 min

    Everything is down. Triage, prioritize, and restore the whole network.