These questions describe a network symptom and ask you to identify the root cause or the correct fix. They appear across all certification exams and reward systematic thinking over memorisation. The best candidates follow a consistent troubleshooting framework even under time pressure.
Start Scenario PracticeRefer to the exhibit. A network engineer is troubleshooting a routing issue. The route for 10.0.0.0/8 is learned via EIGRP with metric 2560512. Which change would most likely cause the metric to increase?
Explanation: The EIGRP metric is calculated using the formula: metric = (K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 * delay) * 256, with default K values (K1=1, K3=1, others=0). Increasing the delay on the outgoing interface (GigabitEthernet0/0) directly increases the delay component in the composite metric, causing the overall metric to increase. Option D is correct because delay is a key variable in the EIGRP metric calculation.
A network administrator is troubleshooting a performance issue in a large enterprise campus network. The network consists of Cisco Catalyst 9300 switches acting as access switches and Cisco Catalyst 9500 switches as distribution. Users on VLAN 10 report intermittent slow file transfers to a server on VLAN 20. The administrator has verified that there are no errors on the links, CPU utilization is normal, and STP topology is stable. The administrator suspects a possible QoS issue. Upon checking the QoS configuration on the access switch, the administrator finds that the default QoS configuration is in place, which trusts the CoS value at the port level. The connected devices are IP phones and PCs; the IP phones mark voice traffic with CoS 5. The server on VLAN 20 is connected to a distribution switch. Which action should the administrator take to most likely resolve the issue?
Explanation: Option C is correct because Auto QoS for VoIP automatically configures the necessary class maps, policy maps, and trust settings to properly classify and queue voice traffic (CoS 5) while ensuring data traffic is not starved. The default QoS configuration trusts CoS at the port level, but without proper queuing and scheduling, voice and data may compete for buffers, causing intermittent slow file transfers. Auto QoS sets up strict priority queuing for voice and allocates bandwidth for data, resolving the performance issue without manual misconfiguration.
Your company has deployed a Cisco Catalyst 9300 switch stack as the distribution layer for a campus network. The network uses VLANs 10 (data), 20 (voice), and 30 (management). The switch stack is configured with DHCP snooping, Dynamic ARP Inspection (DAI), and IP Source Guard (IPSG) on access ports. Recently, users in VLAN 10 report intermittent connectivity issues. You notice that some users receive duplicate IP addresses from the DHCP server. The DHCP server is connected to a trunk port on the switch stack. After reviewing logs, you see that DHCPACK messages are being dropped on the trunk port. The DHCP snooping binding table shows entries for legitimate clients, but also some entries with MAC addresses from a different vendor. Which action should you take to resolve the issue?
Explanation: The DHCP snooping feature treats all ports as untrusted by default, which means DHCP server messages (DHCPOFFER, DHCPACK, DHCPNAK) are dropped on untrusted ports. Since the DHCP server is connected to a trunk port and DHCPACK messages are being dropped, that trunk port must be explicitly configured as a trusted port for DHCP snooping using the 'ip dhcp snooping trust' interface command. This allows legitimate DHCP server responses to reach clients, resolving the duplicate IP address issue caused by clients not receiving their assigned addresses.
An engineer is troubleshooting intermittent connectivity issues between two data center switches. The link is a 10GE LACP port-channel. Which misconfiguration could cause packet loss?
Explanation: Option D is correct because LACP requires one side to be in active mode to initiate negotiation; if one side is active and the other is passive, the passive side will not initiate the LACP exchange, but it will respond to active-side messages. However, the question states that the link is an LACP port-channel, implying both sides should be configured to form the bundle. If one side is passive and the other is active, the port-channel can form, but intermittent packet loss can occur if the passive side fails to respond quickly enough to LACP PDUs during transient conditions, or if there is a mismatch in LACP system priority or port priority that causes the bundle to flap. More critically, a passive/passive combination would never form the port-channel, but active/passive can form it, yet the passive side's reliance on the active side for initiation can lead to instability under certain failure scenarios, causing packet loss.
A network engineer is troubleshooting connectivity issues in a multi-tenant environment where each tenant's traffic is isolated using VRF-Lite. The engineer notices that tenants in the same VRF cannot communicate with each other across different access switches. Which design change should be implemented to enable inter-switch VRF communication?
Explanation: Option B is correct because VRF-Lite requires 802.1Q trunking to extend Layer 3 VRF boundaries across switches. By creating subinterfaces on trunk links and assigning each subinterface to the appropriate VRF, traffic from the same VRF on different switches can be routed through the VRF-specific routing table, enabling inter-switch communication while maintaining isolation.
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Practice all Troubleshooting Scenario QuestionsThese questions describe a network symptom and ask you to identify the root cause or the correct fix. They appear across all certification exams and reward systematic thinking over memorisation. The best candidates follow a consistent troubleshooting framework even under time pressure. These appear throughout the 350-401 and require you to apply your knowledge, not just recall facts.
Cisco doesn't publish an exact breakdown, but scenario-based questions (especially exhibit and command-output formats) make up a significant portion of the 350-401. Practicing each scenario type ensures you're ready for any format.
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