CCNA Network Infrastructure and Connectivity Practice Question
Exhibit
Switch#show interfaces gigabitEthernet 1/0/24
GigabitEthernet1/0/24 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is aabb.cc01.1824 (bia aabb.cc01.1824)
Description: Server-01
Internet address is 192.168.1.10/24
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 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters 00:02:34
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 12000 bits/sec, 12 packets/sec
5 minute output rate 8000 bits/sec, 8 packets/sec
12345 packets input, 1234567 bytes, 0 no buffer
Received 0 broadcasts (0 IP 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
12345 packets output, 1234567 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
Switch#show controllers gigabitEthernet 1/0/24
Interface GigabitEthernet1/0/24
Hardware is Gigabit Ethernet
Media Type: 10/100/1000BaseTX
PHY: Marvell 88E1111
MASTER: internal
Auto-negotiation: enabled
Link Partner Capabilities: 10/100/1000BaseT, Full-duplex
Local Capabilities: 10/100/1000BaseT, Full-duplex
Advertised Capabilities: 10/100/1000BaseT, Full-duplex
Operational: 1000BaseT, Full-duplex
Flow Control: off (both sides)
MDIX: off (crossover cable not detected)
Cable length: 100 meters
Speed: 1000 Mb/s
Duplex: Full
Errors:
CRC errors: 0
Alignment errors: 0
Symbol errors: 0
False carrier: 0
Runts: 0
Giants: 0
Transceiver: internal
DTE status: up
Loopback: none
Last link flapped: 00:00:05 agoA network engineer is troubleshooting intermittent connectivity on an access switch port connected to a server. The output of 'show interfaces gigabitEthernet 1/0/24' shows an increasing number of runts and giants, but no CRC errors. The 'show interfaces status' command indicates the port is in 'err-disabled' state every few hours and must be manually re-enabled. What is the most likely cause of this issue?
⚠ Common exam trap
Cisco often tests the distinction between CRC errors (data corruption) and runts/giants (framing errors) to mislead candidates into thinking duplex mismatch is the cause, but duplex mismatch produces CRC errors and collisions, not runts/giants without CRC errors.
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
✓
Faulty cable or connector causing physical layer errors
Runts and giants without CRC errors indicate a physical-layer issue that corrupts the frame preamble or interframe gap but not the actual data payload. A faulty cable or connector can cause signal degradation leading to these framing errors. The intermittent err-disabled state is typically triggered by link-flap (repeated link up/down events) caused by the unstable physical connection, not directly by alignment or frame-check error counters.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Duplex mismatch between the switch port and the server NIC
Why it's wrong here
Duplex mismatch is characterized by late collisions and CRC errors, not runts or giants. The half-duplex side will retransmit after detecting collisions, causing the full-duplex side to receive truncated frames, but the specific symptom is CRC errors and late collision counts, not exclusively runts. In this scenario, `show controllers` confirms both the switch port and server NIC are 1000 Mb/s Full-duplex, so a duplex mismatch cannot exist.
- ✓
Faulty cable or connector causing physical layer errors
Why this is correct
Runts and giants without CRC errors often indicate physical layer issues like a bad cable, connector, or excessive noise. The cable length at maximum (100 meters) and MDIX off suggest potential signal degradation, leading to intermittent flapping and err-disabled state.
- ✗
Incorrect VLAN configuration on the switch port
Why it's wrong here
VLAN misconfiguration prevents frames from being forwarded correctly only when the 802.1Q tags or access VLAN assignments are mismatched; it doesn't corrupt the physical signal on the wire. The interface error counters for runts and giants increment due to framing violations at the physical layer, which are unaffected by the port's VLAN membership or trunk status. Therefore, while a VLAN mismatch would cause complete loss of connectivity, it would not produce the observed physical-layer frame errors.
- ✗
Speed mismatch between the switch port and the server NIC
Why it's wrong here
Speed mismatch would cause the port to not come up or to flap with errors like CRC errors. The 'show controllers' shows both sides are operating at 1000 Mb/s Full-duplex, so speed mismatch is not present.
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.
✓Faulty cable or connector causing physical layer errorsCorrect answer▾
Why this is correct
Runts and giants without CRC errors often indicate physical layer issues like a bad cable, connector, or excessive noise. The cable length at maximum (100 meters) and MDIX off suggest potential signal degradation, leading to intermittent flapping and err-disabled state.
✗Duplex mismatch between the switch port and the server NICWrong answer — click to see why▾
Why this is wrong here
Duplex mismatch would cause CRC errors and late collisions, which are not present in the exhibit.
✗Incorrect VLAN configuration on the switch portWrong answer — click to see why▾
Why this is wrong here
VLAN mismatch does not cause runts or giants; it causes Layer 2 issues like no connectivity.
✗Speed mismatch between the switch port and the server NICWrong answer — click to see why▾
Why this is wrong here
Speed mismatch would prevent the link from coming up or cause CRC errors, but the link is up at 1000 Mb/s.
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?”
Go deeper
Related to this question
Learn chapter
Network Topology Types
Key term
Cyclic Redundancy Check
A Cyclic Redundancy Check (CRC) is an error-detecting code used to verify that data transmitted over a network or stored on a device has not been corrupted.
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
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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.