Troubleshooting Flashcards

A switch port is in 'err-disabled' state. What is the most common cause of this condition?

Answer: Port security violation

Port security violations are the most common cause of a port entering the err-disabled state when the maximum MAC address count is exceeded.

When troubleshooting a VLAN connectivity issue, a host in VLAN 10 cannot communicate with a host in VLAN 20. What is required for inter-VLAN communication?

Answer: A Layer 3 device or router-on-a-stick configuration

Inter-VLAN routing requires a Layer 3 device such as a router or multilayer switch to route traffic between VLANs.

You cannot Telnet to a remote router. The 'show line vty 0 4' output shows no password set. What must you configure?

Answer: VTY line password

A VTY line password must be configured with the 'password' command and 'login' enabled for Telnet access to succeed.

A router interface shows 'FastEthernet0/0 is up, line protocol is down.' What is the most likely cause?

Answer: Keepalive mismatch or encapsulation issue

Up/down status means the physical layer is functional but Layer 2 is failing, typically due to a keepalive or encapsulation mismatch.

Which command should you use to verify that NAT translations are occurring correctly on a Cisco router?

Answer: show ip nat translations

'show ip nat translations' displays active NAT translation entries showing inside local and global address mappings.

A user reports they can reach some websites but not others. DNS resolution seems to be working. What should you check next?

Answer: Routing table for specific destination routes

If DNS works and some sites are reachable, specific routing issues or ACLs may be blocking certain destinations in the routing table.

After adding a new static route, traffic still doesn't flow to the destination. Which command verifies the route was correctly added?

Answer: show ip route

'show ip route' displays the active routing table and confirms whether the static route is installed and reachable.