CCNA Break/Fix II: Read the Symptom

A dual-stack static routing lab with a subtle IPv6-only failure. IPv4 reaches across the WAN from a branch PC to an HQ server and loopback, while IPv6 to the same destinations fails. The IPv6 addressing on interfaces is correct; the break lies elsewhere. Compare what IPv4 knows versus what IPv6 knows for the same four destinations and make IPv6 match the working IPv4 design.

A security audit showed that routers accepted SSH from outside the management LAN despite an existing filter. Diagnose how the management ACL is bound to the VTY lines and make it govern which inbound sessions the routers accept, without breaking data-plane reachability.

A replacement branch router came up on three carrier handoffs. All subinterfaces and /30s look correct and line protocols are up, yet no traffic passes. Your job: read what each circuit actually puts on the wire and bring the branch into alignment with the remote ends — including the carrier-published IP MTU on one circuit — without altering addressing or static routes.

Daily CCNA troubleshooting repair: two branch floors were renumbered and now users report DHCP failures and no Internet access. Work end-to-end from each floor’s client to the WAN: trace DHCP pool-to-interface bindings, validate NAT policy per floor, and restore both floors so leases are issued from the new plan and both can reach the provider loopback.

An overnight hardening change reached the core but not the branches. By morning, both OSPF adjacencies to the core were down even though every point-to-point link still pings and no addressing changed. Restore end-to-end reachability by diagnosing what the core and each spoke now disagree about on the carrier-facing transits and finishing the change on the branch ends.

Two sites have dual WAN links (primary and backup). Both circuits are up and end-to-end connectivity works, yet every intersite flow rides the slow backup path. Your job: read which routes each router actually installed for the opposite site and why, then restore the intended path preference so traffic uses the primary circuit while keeping the backup standing by.

A DMZ server was rebuilt onto a new IP last week. Since then, outside users cannot open its three published services, while the server itself can browse out normally. Your job: work from the public address toward the inside, diagnose where the forwarding breaks, and republish all three services on the advertised public IP without disrupting outbound internet access.

An office floor’s redundant default gateway pair keeps needing manual intervention. During an uplink outage the active gateway stays active and strands users, and when the repaired router returns it seizes the VIP immediately and the floor bounces. Troubleshoot the pair’s failover behavior by examining what each router monitors and when it is allowed to take the role back. Bring the pair into compliance with the convergence standard without changing anything else.

Two internal subnets behind a branch router stopped working after a summarization tidy-up. Everything else inside the same /16 summary is fine, and the edge still has a discard route for the summary. Your job: trace which route each hop actually matches for those destinations, then restore reachability without removing or weakening the summary.

Troubleshoot a dual-stack hub-and-spoke where IPv6 traffic never flowed after go-live. IPv4 works end-to-end, but IPv6 static routes are present in running-config and missing from the RIB. Compare configured vs installed routes, trace next-hop reachability per link, and correct the next-hop so each static becomes active. Validate from the user LAN.

A late-night rollback restored configs from before a WAN carrier change. Since then, both branches report OSPF neighbors that appear, start exchanging, and then reset—never reaching FULL. Users at Branch A cannot reach Branch B. Your task is to observe the partial adjacency behavior, isolate why the database exchange never completes, and restore the carrier’s standard everywhere it applies so reachability returns end-to-end.

A full-path break/fix capstone for CCNA troubleshooting. A single floor was renumbered and re-cabled. Users on that floor cannot reach anything — not their default gateway, not other subnets, and not the internet. The change record mentions both the access switch and the internet edge. Your job: prove the path hop-by-hop from the client outward and repair every break. Fixing only one side does not change the symptom; both layers must be corrected.