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Network Infrastructure and Connectivity →hardMultiple ChoiceObjective-mapped

Err-Disabled Port: Runts and Giants from Faulty Cable

This 200-301 practice question tests your understanding of network infrastructure and connectivity. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

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 ago

A 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?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

  • Clue: "most likely"

    Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

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 ago

Quick Answer

The answer is a faulty cable or connector causing physical layer errors. This is correct because runts and giants without CRC errors indicate the physical medium is corrupting the frame’s preamble or interframe gap rather than the data payload itself, so the CRC check still passes. On the CCNA 200-301 v2 exam, this scenario tests your ability to distinguish physical-layer issues from data-link problems: a bad cable triggers link-flap, which the switch detects and punts the port into err-disabled state to prevent instability. A common trap is to blame duplex mismatch or speed negotiation, but those would produce CRC errors alongside runts and giants. Remember the memory tip: “No CRC, blame the cable” — if CRC is clean but runts and giants climb, the fault is in the physical connection, not the protocol.

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.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 typically causes CRC errors and late collisions, not runts and giants. The 'show controllers' shows both sides are Full-duplex, so duplex mismatch is unlikely.

  • ✓

    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.

    Clue confirmation

    The clue word "most likely" in the question point toward this answer.

    Related concept

    Read the scenario before looking for a memorised answer.

  • ✗

    Incorrect VLAN configuration on the switch port

    Why it's wrong here

    VLAN mismatch causes connectivity issues but does not produce runts or giants. It would result in packets being dropped at Layer 2, not physical layer 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?”

Common exam traps

Common exam trap: answer the scenario, not the keyword

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.

Trap categories for this question

  • Command / output trap

    Duplex mismatch typically causes CRC errors and late collisions, not runts and giants. The 'show controllers' shows both sides are Full-duplex, so duplex mismatch is unlikely.

Detailed technical explanation

How to think about this question

Runts are frames smaller than 64 bytes, and giants are frames larger than 1518 bytes (or 1522 with VLAN tagging). These errors often arise from faulty cabling, electromagnetic interference, or a failing NIC that corrupts the frame delimiter or length field. The err-disabled state is triggered by the switch's error-disable feature when a port exceeds a threshold of such errors, requiring manual or automatic recovery via 'errdisable recovery cause' commands.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 200-301 question test?

Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: 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.

What should I do if I get this 200-301 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 11, 2026

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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.