AdvancedDailyLocked
CCNP VRF & GRE Capstone: The Overlay That Came Back Wrong
HQ and the branch came back from a provider change unable to reach each other. Bring the overlay back to its design.
Topic
CCNA troubleshooting labs
74 hands-on Troubleshooting scenarios you build in your own Cisco Modeling Labs instance and grade against the answer key. Fault-finding practice for CCNA and CCNP.
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AdvancedDailyLocked
CCNA L3 Switching Capstone: Building B Came Back Wrong
Building B came back from maintenance broken: staff PCs get no address and the kiosks can't reach their gateway.
AdvancedDailyLocked
CCNA Break/Fix Capstone: One Floor, Two Layers, One Ticket
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.
AdvancedDailyLocked
CCNA Break/Fix: The Adjacency That Forms and Never Finishes
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.
AdvancedDailyLocked
CCNA Break/Fix: Routes Configured, Never Installed
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.
AdvancedDailyLocked
CCNA Break/Fix: Subnets That Went Dark After Summary Tidy
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.
AdvancedDailyLocked
CCNA Break/Fix: The Gateway Pair That Only Fails Over by Hand
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.
IntermediateDailyLocked
CCNA Break/Fix: Published Services Nobody Outside Can Open
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.
IntermediateDailyLocked
CCNA Break/Fix: Everything Is Crossing the Backup Circuit
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.
IntermediateDailyLocked
CCNA Break/Fix: Both Branches Went Quiet at 02:14
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.
IntermediateDailyLocked
CCNA Break/Fix: The Renumbering That Left Two Floors Offline
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.
IntermediateDailyLocked
CCNA Break/Fix: Three Circuits That Test Clean and Carry Nothing
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.
BeginnerDailyLocked
CCNA Break/Fix: The Management Filter That Guards Nothing
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.
BeginnerDailyLocked
CCNA Break/Fix: IPv4 Crosses the WAN and IPv6 Does Not
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.
BeginnerDailyFree2026-09-15
CCNA Break/Fix: The Branches the Core Cannot See
Daily CCNA troubleshooting drill: Two branches can ping the core over their transit links, yet the core does not learn any branch routes. Your job is to trace how OSPF is enabled on each device, isolate why the core’s routing table is missing the branch LANs and loopbacks, and bring both branches into the correct OSPF area without changing how the core enables it.
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AdvancedDailyLocked
CCNA Break/Fix Capstone: One Symptom, Two Faults
A branch user in VLAN 10 cannot reach the data center's line-of-business server, stalling the end-of-day batch upload. Two faults sit behind the one complaint, and clearing either alone leaves the user where they started. The client gets no answer from its own gateway either.
AdvancedDailyLocked
CCNA Break/Fix: The ACL That Blocks Too Much
Branch staff cannot reach the server at 172.16.100.100, and they cannot close a day's tickets without it. Policy also requires Telnet from the user LAN to that server be denied while everything else passes, and the security review cannot confirm it is being enforced. Work the path from a client and find what is wrong.
IntermediateDailyLocked
CCNA Break/Fix: Translation Happens, Replies Do Not
A branch reaches its provider through one edge router that hides the user LAN behind its upstream address. Since a change window, everyone on 192.168.10.0/24 reports that nothing beyond the branch answers, while the router itself reaches the provider's test address. Find what is wrong.
IntermediateDailyLocked
CCNA Break/Fix: The DHCP Request That Goes Nowhere
Branch staff cannot work: no workstation on the user LAN holds an address. By design, clients there lease from the hub router's scope and the two sites route to each other statically. Find why no lease arrives; change nothing else.
IntermediateDailyLocked
CCNA Break/Fix: The OSPF Neighbour That Never Forms
A regional retailer's branch lost core access after last night's maintenance window. Users reach their gateway and the routers ping across the transit, but no OSPF neighbour appears and the branch LAN is missing from the core's table. The documented design is OSPF process 1, area 0 on both routers. Restore the adjacency without changing addressing or adding static routes.
BeginnerDailyLocked
CCNA Break/Fix: The Root Bridge Nobody Elected
A campus triangle of one distribution and two access switches carries VLAN 10 and VLAN 20. After an access-switch replacement, users report slower cross-campus response: hosts still reach each other, and the layer 2 path no longer matches a design that roots both VLANs at SW-CAMPUS-DIST1.
BeginnerDailyFree2026-08-24
CCNA Break/Fix: The Trunk That Carries Only Some VLANs
Your team supports a small campus access layer: two switches, one 802.1Q trunk. The help desk reports VLAN 20 users cannot reach their peers while VLAN 10 users can, and both ends read up and trunking. Campus design: VLANs 10 and 20 are the only VLANs any trunk carries; every trunk's native VLAN is 999.
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AdvancedDailyLocked
CCNA: IPv6 Won't Ping — Work the Failure, Not the Config
A dual-stack enterprise tri-router line with two LANs and end hosts. IPv4 routing is healthy and end-to-end; IPv6 addressing is present but end-to-end IPv6 fails. Work from operational state only to isolate and correct the broken IPv6 control/forwarding plane without changing what already works. The graded end-state requires IPv6 forwarding enabled on all routers, OSPFv3 process 10 in area 0 with an explicit unique router-id on every router, and per-interface activation on all required links so the hosts can ping6 across the WAN.
IntermediateDailyLocked
CCNA EtherChannel: Why Won't It Bundle?
Troubleshoot and fix an LACP EtherChannel between campus switches so both physical members bundle and the trunk reliably carries VLAN 10. Two independent faults are seeded: an intra-bundle trunk mismatch on one switch and an administratively down member on the other. Learners diagnose with show commands, align trunk attributes, and verify end-to-end host reachability.
Practicing network troubleshooting on Cisco Modeling Labs
Why it matters, and what these labs cover.
Configuration labs teach you to build a network that works. They do not teach you what to do at 2am with a network that used to work. Troubleshooting is a different skill: forming a hypothesis, choosing the one command that will disprove it fastest, and resisting the urge to change three things at once. It is also the skill both the CCNA and CCNP exams weight heavily, and the one candidates practise least, because a broken lab is much harder to author than a working one.
The break/fix, repair and troubleshooting-capstone labs here ship with faults already in the running-config: you import a network that is genuinely broken and find out why. Others are build labs with a troubleshooting section. The faults are the ones that actually occur: a native VLAN mismatch, a trunk missing the VLAN it needs to carry, an OSPF area or timer mismatch, an ACL applied in the wrong direction, a NAT pool that doesn't cover the inside network, a next-hop that isn't reachable, a shutdown interface nobody mentions. You work them the way you would in production — show and debug to narrow it down, one change at a time — then upload the repaired config, and the grader checks the network reaches the intended end state rather than just that you typed something plausible.
Frequently asked questions
How are the faults injected?
In the labs that start broken, they are built into the starter configuration you import, so the lab is broken from the first boot exactly as a production network would be. Nothing tells you which device is at fault — finding that out is the exercise.
Do the labs tell me what the fault was afterwards?
Yes. Once you submit, the node-by-node solution reveals, so you can compare the fix you made against the intended one — including the cases where you found a different valid repair.
What if I get completely stuck?
Each lab lists its troubleshooting focus up front, so you know which area the fault lives in without being told the answer. That keeps the exercise honest while stopping a single missed detail from costing you an evening.
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