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#CiscoswitchingInterviewquestions&answers for L1 level engineer: 1. How do you troubleshoot a switch port that is not coming up? Check Physical Connections: Ensure the cable is connected properly and that the device at the other end is powered on. Check Port Status: Use the command #show interface [interface ID] to check if the port is administratively down or physically down. Verify VLAN Membership: Make sure the port is assigned to the correct VLAN using show vlan brief. Check for Errors: Look for any errors like err-disabled using #show interface [interface ID]. Check Auto-negotiation: Verify if the port settings (speed, duplex) are correct and match the device on the other end. Use show interface status to identify mismatch. 2. How would you troubleshoot a trunk link that is not passing VLANs correctly? Verify Trunk Configuration: Use show interface trunk to check the trunking status and verify the allowed VLANs. Check VLAN Configuration: Make sure the correct VLANs are defined using show vlan brief. Check Native VLAN Mismatch: Ensure that the native VLAN on both ends of the trunk match. If they do not, the traffic might not pass correctly. Verify Encapsulation: Use #show interfaces [interface] to ensure that both ends of the trunk are using the same encapsulation type (e.g., 802.1Q). Verify DTP (Dynamic Trunking Protocol): Check if the switch ports are properly negotiating trunking. If not, you can force trunking with the command switchport mode trunk. 3. What is the cause and solution for a port being in an 'err-disabled' state? A port can enter the 'err-disabled' state due to several reasons, including: Security violations (port security). Link flapping (the port keeps going up and down). STP topology changes. Duplex mismatches. BPDU guard violations. To resolve: Check the reason for the error using #show interface [interface ID] and #show log. Resolve the issue (e.g., fix security violation, check physical cables, or correct duplex mismatch). Re-enable the port with shutdown followed by no shutdown. 4. How would you troubleshoot a situation where a user is unable to access resources in a different VLAN? VLAN Configuration: #show vlan brief – Verify port is in the correct VLAN. VLAN Routing: Ensure inter-VLAN routing is enabled (Layer 3 switch/router). IP Addressing: Verify correct IP, subnet mask, and gateway. ACLs: Ensure no ACLs block VLAN traffic. Trunking: #show interface trunk – Ensure trunk allows the VLAN. 5. How would you verify the health of the switch and its interfaces? Interface Status: #show interface status – Check status and VLAN. #show interfaces – Check errors and traffic. System Resources: #show processes – Monitor CPU usage. #show memory – Check memory usage. Errors: #show logging – View system logs. #show interface [interface ID] – Check interface status and errors. Spanning Tree: #show spanning-tree – Verify root bridge and loops. #networking #switching #L1interview #ccna