Exhibit
R1# show interfaces GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up (connected)
Hardware is iGbE, address is 0011.2233.4455 (bia 0011.2233.4455)
Internet address is 192.168.100.1/24
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s, media type is 10/100/1000BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output 00:00:01, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 1000 bits/sec, 2 packets/sec
5 minute output rate 5000 bits/sec, 3 packets/sec
52345 packets input, 10243456 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
5231 input errors, 5200 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
245678 packets output, 54839203 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out- A
The interface is configured with an incorrect encapsulation type.
Why wrong: The output shows 'Encapsulation ARPA', which is the standard Ethernet encapsulation. If the wrong encapsulation were configured, the interface would likely go down or show encapsulation mismatches, not high CRC counts.
- B
A damaged or faulty cable is causing excessive CRC errors.
The exhibit displays 5200 CRC errors (more than 5000) and 5231 input errors. High CRC counts directly indicate that received frames are being corrupted by physical layer issues such as a damaged cable, loose connector, or EMI on the copper segment.
- C
A duplex mismatch exists between the connected devices.
Why wrong: The interface is running at full-duplex and shows zero collisions, late collisions, or runts. A duplex mismatch would typically exhibit collisions, late collisions, or runts on the half‑duplex side, none of which appear.
- D
The interface is assigned to the wrong VLAN.
Why wrong: VLAN assignment errors cause connectivity failures, not physical‑layer errors. The output shows no VLAN-specific counters like 'unknown protocol drops' related to VLAN mismatches, and the interface is otherwise passing traffic.
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