ICND1 Troubleshooting 3 — Questions and Answers
Question 1: A switch port is in 'err-disabled' state. What is the most common cause of this condition?
- Wrong VLAN assignment
- Port security violation (Correct answer)
- Incorrect duplex setting
- STP topology change
Correct 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.
Question 2: 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?
- A trunk link between the switches
- A Layer 3 device or router-on-a-stick configuration (Correct answer)
- Spanning Tree Protocol adjustment
- Setting both hosts to the same VLAN
Correct 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.
Question 3: You cannot Telnet to a remote router. The 'show line vty 0 4' output shows no password set. What must you configure?
- Enable secret password
- VTY line password (Correct answer)
- Console password
- SSH version 2
Correct answer: VTY line password
A VTY line password must be configured with the 'password' command and 'login' enabled for Telnet access to succeed.
Question 4: A router interface shows 'FastEthernet0/0 is up, line protocol is down.' What is the most likely cause?
- No IP address configured
- Keepalive mismatch or encapsulation issue (Correct answer)
- Interface is administratively shut down
- No cable connected to the interface
Correct 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.
Question 5: Which command should you use to verify that NAT translations are occurring correctly on a Cisco router?
- show ip route
- show ip nat translations (Correct answer)
- show interface statistics
- debug ip ospf events
Correct answer: show ip nat translations
'show ip nat translations' displays active NAT translation entries showing inside local and global address mappings.
Question 6: A user reports they can reach some websites but not others. DNS resolution seems to be working. What should you check next?
- Default gateway on the user's PC
- Routing table for specific destination routes (Correct answer)
- ARP cache on the switch
- VLAN membership of the user's port
Correct 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.
Question 7: After adding a new static route, traffic still doesn't flow to the destination. Which command verifies the route was correctly added?
- show running-config
- show ip route (Correct answer)
- show ip protocols
- show interface brief
Correct answer: show ip route
'show ip route' displays the active routing table and confirms whether the static route is installed and reachable.
ICND1 Troubleshooting 3
A switch port is in 'err-disabled' state.
What is the most common cause of this condition?