CCNA
793 incident response problems that help with CCNA prep.
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All problems (793)
NETWORK-017Internal DNS search-domain order attaches to a different service with the same nameInternal DNS search-domain order attaches to a different service with the... is a hands-on troubleshooting drill. Covers a search-domain setting problem where a short-name call resolves to a different service than intended. DNS and Routing needs to be checked by narrowing scop...NetworkBeginner15 minFreeNETWORK-011A proxy-header problem that works with curl but looks like a CORS error only in the browserA proxy-header problem that works with curl but looks like a CORS error only... is a hands-on troubleshooting drill. A situation where it is not an actual network outage but a response-header policy that fails only browser requests. NGINX Firewall and Proxy Paths needs to be c...NetworkBeginner16 minFreeNETWORK-014The port is open but a reverse path filter keeps the response from returningA situation where incoming connections are visible but response packets are blocked by kernel policy, so the session never establishes.NetworkBeginner18 minFreeNETWORK-072LACP bundle never forms after a stack replacementCabling is correct, but the upstream sees a different partner identity and refuses to aggregate the links into the expected bundle.NetworkIntermediate16 minFreeNETWORK-107DHCP relay uses the correct helper address but the source interface belongs to the wrong VRF so replies never returnDiscover messages leave the switch, yet offers vanish because the server replies into a routing context that has no path back to the client segment.NetworkIntermediate17 minFreeNETWORK-079OSPF virtual link stays downArea IDs still look familiar, but the virtual link cannot form because the transit area assumptions were broken during a partial topology cleanup.NetworkIntermediate17 minFreeNETWORK-068Port-channel min-links keeps the bundle down after a partial member failureOne physical path still forwards traffic, but the logical interface remains down because the configured minimum bundle size is no longer satisfied.NetworkIntermediate17 minFreeNETWORK-084Spanning-tree guard blocks one hypervisor uplinkThe network configuration is stable, but a host starts sending unexpected bridge protocol units and the protection feature shuts the access port down.NetworkIntermediate17 minFreeNETWORK-080MAC flapping alarms appearThe network is stable, but one mobile workload triggers MAC move alarms and intermittent forwarding loss because the switching design assumes slower host movement.NetworkIntermediate18 minFreeNETWORK-054VRRP stays on the backup routerFailover worked during the incident, but the original priority path never resumes because preemption policy no longer matches the intended steady state.NetworkIntermediate18 minFreeNETWORK-057Dynamic ARP inspection drops a host after a static IP move without updated bindingsLayer2 connectivity looks normal, but one endpoint stops talking because the protection policy still trusts the old DHCP or ARP binding state.NetworkIntermediate19 minFreeNETWORK-037Internal clients cannot reach the public VIPExternal users can access the service normally, but inside clients fail when they resolve the same public name because the edge path does not support loopback NAT.NetworkIntermediate20 minFreeNETWORK-033Cross-vendor EtherChannel failsThe bundle comes up on one side only, leaving traffic hashed inconsistently, because the two platforms are not negotiating the channel mode the same way.NetworkIntermediate23 minFreeNETWORK-075IPv6 RA guard blocks the real router after a campus template is copied to the uplinkIPv4 still works, but IPv6 clients lose their gateway because the edge protection template was applied to the wrong interface type.NetworkIntermediate15 minFreeNETWORK-087Router-on-a-stick subinterface works for one VLAN but the allowed list omits the new segmentInter-VLAN routing exists overall, but the newly added segment remains isolated because the trunk never allowed that VLAN onto the router link.NetworkIntermediate15 minFreeNETWORK-094VLAN exists on both switches but VTP pruning removes the path users think is activeThe database is correct, yet traffic still disappears because dynamic pruning removed the VLAN from a trunk users assumed was always carrying it.NetworkIntermediate15 minFreeNETWORK-106A QinQ handoff preserves the service VLAN but rewrites the inner PCP bits so voice traffic loses priorityConnectivity remains intact, but quality degrades because the handoff normalizes priority bits the downstream voice design expected to preserve.NetworkIntermediate16 minFreeNETWORK-082Access switch uplink looks up but the native VLAN changed and voice phones never get the right DHCP scopeLink status is healthy, yet phone onboarding fails because the expected voice and management traffic classification changed with the trunk native VLAN baseline.NetworkIntermediate16 minFreeNETWORK-092EtherChannel load-balancing hash sends one chatty flow over the only degraded member linkMost traffic looks normal, but one application suffers because its flow hash repeatedly lands on the weakened physical member of the bundle.NetworkIntermediate16 minFreeNETWORK-069Internal clients cannot reach the public VIPExternal users connect normally, yet internal users fail on the same FQDN because the firewall does not hairpin the connection back to the inside service path.NetworkIntermediate16 minFree