CCNA Network Infrastructure and Connectivity Practice Question
Exhibit
ServerFarm-SW1# show controllers GigabitEthernet0/1
Interface GigabitEthernet0/1
Hardware is Gigabit Ethernet
Media Type: 1000BaseSX SFP
Link Status: Up
Auto-negotiation: off
Speed: 1000 Mbps
Duplex: Full
Transmit Errors: 0
Receive Errors: 0
CRC Errors: 0
Frame Errors: 0
Runts: 0
Giants: 0
Input Errors: 0
Output Errors: 0
Collisions: 0
Late Collisions: 0
Deferred: 0
Lost Carrier: 0
No Carrier: 0
FCS Errors: 0
Symbol Errors: 0
ServerFarm-SW1# show interfaces GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is up
Hardware is Gigabit Ethernet, address is 0011.2233.4455 (bia 0011.2233.4455)
Description: Uplink to Access-SW1
Internet address is 192.168.1.2/30
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 SX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/2000/0/0 (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 1000 bits/sec, 2 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 2 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
ServerFarm-SW1# show interfaces status
Port Name Status Vlan Duplex Speed Type
Gi0/1 Uplink to Access-SW1 connected trunk full 1000 1000BaseSX SFP
Gi0/2 Server1 connected 100 full 1000 10/100/1000BaseTX
Gi0/3 Server2 connected 100 full 1000 10/100/1000BaseTXA network engineer notices that users on VLAN 100 are experiencing intermittent connectivity to the server farm. The switch connecting these users shows no errors on the uplink interface, but the server farm switch reports a high number of input errors on its connected interface. The engineer runs 'show controllers' on the server farm switch. What is the most likely cause of the issue?
⚠ Common exam trap
Cisco often tests the distinction between 'show interfaces' (which shows input errors but not the specific physical-layer cause) and 'show controllers' (which reveals the exact physical-layer errors), leading candidates to mistakenly choose duplex mismatch or cable length issues without recognizing that the command output points to SFP or transceiver problems.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SFP module is faulty or incompatible with the cable type.
The 'show controllers' command on the server farm switch reveals physical-layer issues such as framing errors, CRC errors, or alignment errors, which are often caused by faulty or incompatible SFP modules. Since the uplink interface on the user switch shows no errors, the problem is isolated to the server farm switch's interface, and a faulty SFP can introduce signal degradation or electrical issues without necessarily causing complete link failure. Option B is correct because SFP incompatibility or defects commonly produce input errors at the physical layer, even when the link appears up.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The interface is configured with the wrong duplex setting.
Why it's wrong here
Duplex mismatch would make the interface show half-duplex on one side or cause a dramatic increase in late collisions and CRC errors on the suspect side. The provided output confirms Full-duplex on the local interface, and the remote switch also reports full duplex within its own negotiated settings; moreover, gigabit fiber links do not use half-duplex unless explicitly forced. Because the link is up and neither side reports runts, collisions, or late-collision counters, a duplex configuration problem cannot be the root cause.
- ✓
The SFP module is faulty or incompatible with the cable type.
Why this is correct
The 'show controllers' output shows the media type as 1000BaseSX SFP with auto-negotiation off, but the interface is reporting no errors. However, the other switch sees input errors. This points to a hardware issue with the SFP, such as a faulty module or a mismatch between the SFP and the fiber cable (e.g., using a single-mode SFP with multi-mode fiber).
- ✗
The cable is too long, causing attenuation.
Why it's wrong here
Although excessive fiber length can attenuate the optical signal below the receiver's sensitivity threshold, attenuation typically manifests as a high rate of FCS errors, symbol errors, or input errors on the interface. The 'show controllers' output for the local switch shows no such error counters, and the link is fully up at 1000 Mbps. For 1000BaseSX multimode, the distance limit is 220 m (OM1) or 550 m (OM2), so a length issue would have to be extreme and would not selectively cause errors only on the remote switch without physical-layer alarms.
- ✗
Auto-negotiation is disabled, causing a speed mismatch.
Why it's wrong here
Speed is set to 1000 Mbps on both ends, and auto-negotiation is off, which is normal for fiber connections. Speed mismatch would cause the link to not come up or show errors, but the link is up and no errors are reported here.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The SFP module is faulty or incompatible with the cable type.Correct answer▾
Why this is correct
The 'show controllers' output shows the media type as 1000BaseSX SFP with auto-negotiation off, but the interface is reporting no errors. However, the other switch sees input errors. This points to a hardware issue with the SFP, such as a faulty module or a mismatch between the SFP and the fiber cable (e.g., using a single-mode SFP with multi-mode fiber).
✗The interface is configured with the wrong duplex setting.Wrong answer — click to see why▾
Why this is wrong here
The 'show controllers' output confirms Full-duplex on both ends, so a duplex mismatch is not the cause. Duplex mismatch would typically cause collisions or CRC errors, which are not indicated here.
Why candidates choose this
Students often associate input errors with duplex mismatch, as it is a common cause of errors on Ethernet links. However, the output clearly shows both ends are set to Full-duplex, ruling this out.
✗The cable is too long, causing attenuation.Wrong answer — click to see why▾
Why this is wrong here
While excessive cable length can cause attenuation and errors, the 'show controllers' output does not show specific error counters like symbol errors or FCS errors that would indicate attenuation. The link is up and no errors are reported on this switch, making cable length an unlikely cause.
Why candidates choose this
Cable length is a known cause of signal degradation and errors, so students might jump to this conclusion. However, the absence of related error counters and the fact that errors are only seen on one side suggest a hardware issue rather than a cable length problem.
✗Auto-negotiation is disabled, causing a speed mismatch.Wrong answer — click to see why▾
Why this is wrong here
Speed is set to 1000 Mbps on both ends, and auto-negotiation is off, which is normal for fiber connections. A speed mismatch would prevent the link from coming up or cause constant errors, but the link is up and no errors are reported on this switch.
Why candidates choose this
Auto-negotiation is often misunderstood; students may think disabling it always causes issues. However, for fiber Gigabit Ethernet, auto-negotiation is optional and speed is typically fixed. The absence of errors on this switch indicates speed mismatch is not the problem.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
Go deeper
Related to this question
Learn chapter
Network Topology Types
Key term
VLAN
A VLAN (Virtual Local Area Network) is a logical grouping of network devices that behave as if they are on the same physical network segment, regardless of their actual physical location.
Key term
CRC
CRC (Cyclic Redundancy Check) is an error-detecting code used to detect accidental changes to raw data in digital networks.
About these practice questions
Courseiva writes every 200-301 question from scratch — 1,389 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.