Troubleshooting Flashcards
7 cards from real ICND1 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Troubleshooting flashcards as text
A router shows 'Serial0/0 is down, line protocol is down.' What is the FIRST step to troubleshoot this issue?
Answer: Check the physical cable and CSU/DSU
A down/down state indicates a Layer 1 physical problem, so checking the cable and CSU/DSU is the appropriate first step.
Which command would you use to verify that CDP neighbors are being detected on a Cisco switch?
Answer: show cdp neighbors
'show cdp neighbors' displays directly connected Cisco devices discovered via the Cisco Discovery Protocol.
A host can ping its default gateway but cannot reach remote networks. What should you check on the router?
Answer: Routing table on the router
If the gateway is reachable but remote networks are not, the router's routing table likely lacks the necessary routes.
The output of 'show interface FastEthernet0/0' shows 'input errors' incrementing. What does this most likely indicate?
Answer: Duplex mismatch or bad cable causing CRC errors
Input errors, especially CRC errors, are commonly caused by duplex mismatches or physical layer problems like damaged cables.
You issue 'ping 10.1.1.1' from a router and receive 'U.U.U.' in the output. What do the 'U' characters indicate?
Answer: The destination is unreachable
A 'U' in ping output represents an ICMP Destination Unreachable message received back from a router.
A technician runs 'show ip route' and sees a route marked with 'C'. What does the 'C' designation mean?
Answer: The route is a directly connected network
The 'C' code in the routing table indicates a directly connected network on an active interface.
Which Cisco IOS command displays the Layer 2 to Layer 3 address mappings learned by a router?
Answer: show ip arp
'show ip arp' displays the ARP cache, which maps IP addresses to MAC addresses on connected segments.