ICND1 Troubleshooting 4 — Questions and Answers
Question 1: A host receives an APIPA address (169.254.x.x). What does this indicate about the network?
- The host is configured with a static IP
- The DHCP server is unreachable or not responding (Correct answer)
- The DNS server is down
- The default gateway is misconfigured
Correct answer: The DHCP server is unreachable or not responding
An APIPA address means the host failed to receive a DHCP lease and self-assigned an address in the 169.254.0.0/16 range.
Question 2: Which debug command would help identify why OSPF neighbor adjacencies are not forming?
- debug ip rip
- debug ip ospf adj (Correct answer)
- debug ip nat
- debug ip packet
Correct answer: debug ip ospf adj
'debug ip ospf adj' shows OSPF adjacency events and error messages that explain why neighbor relationships fail to establish.
Question 3: A switch trunk port shows only the native VLAN in 'show interface trunk' output. What is likely misconfigured?
- The native VLAN ID
- VLANs not added to the allowed list on the trunk (Correct answer)
- Spanning tree port cost
- The switch priority value
Correct answer: VLANs not added to the allowed list on the trunk
If VLANs are not explicitly permitted on a trunk, they will not be carried across it, resulting in only the native VLAN being active.
Question 4: You suspect an access list is blocking traffic. Which command shows all configured ACLs and their match statistics?
- show ip interface brief
- show access-lists (Correct answer)
- show ip route
- show running-config interfaces
Correct answer: show access-lists
'show access-lists' displays all configured access control lists along with match counters for each ACE.
Question 5: A router has two paths to the same destination, one via OSPF and one via RIP. Which path will be preferred and why?
- RIP, because it uses fewer hops
- OSPF, because it has a lower administrative distance (Correct answer)
- RIP, because it has a lower administrative distance
- OSPF, because it always wins over RIP regardless of metrics
Correct answer: OSPF, because it has a lower administrative distance
OSPF has an administrative distance of 110 versus RIP's 120, so the router will prefer the OSPF route.
Question 6: After replacing a switch, users report intermittent connectivity. 'Show spanning-tree' shows topology changes. What is likely happening?
- VLANs are not configured on the new switch
- STP is reconverging due to the new switch (Correct answer)
- The switch has a duplicate IP address
- Port security is blocking multiple MAC addresses
Correct answer: STP is reconverging due to the new switch
Adding a new switch triggers STP reconvergence, causing temporary traffic interruptions as the topology stabilizes.
Question 7: A router's CPU utilization is at 99%. Which command helps identify the process consuming the most CPU?
- show interface counters
- show processes cpu (Correct answer)
- show memory statistics
- show ip traffic
Correct answer: show processes cpu
'show processes cpu' lists all IOS processes with their CPU utilization percentages, identifying the top consumer.
ICND1 Troubleshooting 4
A host receives an APIPA address (169.254.x.x).
What does this indicate about the network?