CCNA Network Infrastructure and Connectivity Practice Question
Which TWO of the following are valid interpretations of errors seen in the output of the 'show interface' command?
⚠ Common exam trap
Cisco often tests the exact byte thresholds for runts (less than 64 bytes) and giants (greater than 1518 bytes), and candidates frequently reverse these values or confuse them with other error types.
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
✓
CRC errors indicate that frames were received with an invalid checksum, often due to cabling issues.
CRC errors (option A) indicate frames with an invalid checksum, often due to cabling issues, which is correct. Option D is also correct: 'Input errors' is a cumulative counter that includes runts, giants, CRC errors, and frame errors. Option B is wrong because runts are frames smaller than 64 bytes, not larger. Option C is wrong because giants are frames larger than the maximum allowed size (typically 1518 bytes), not smaller than 64 bytes. Option E is wrong because 'flaps' refer to an interface going up and down repeatedly, not necessarily physically disconnected; it could be due to duplex mismatch or other reasons.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
CRC errors indicate that frames were received with an invalid checksum, often due to cabling issues.
Why this is correct
A CRC error means the Ethernet frame's frame check sequence (FCS) computed at the receiver does not match the value transmitted, indicating corruption during transit. This is commonly caused by faulty cabling, bad connectors, electromagnetic interference, or a marginal transceiver, rather than by a software issue. CRC errors may also be accompanied by alignment errors if the corruption shifts bit boundaries, pointing further to a physical-layer problem.
- ✗
Runts are frames that are larger than the maximum allowed size.
Why it's wrong here
Runts are frames that fall below the 64-byte minimum Ethernet frame size, not above the maximum. The maximum is 1518 bytes (or 1522 with VLAN tagging, and jumbo frames up to 9216 bytes on some switches). A frame exceeding that upper limit is a giant—so this option reverses the definitions entirely.
- ✗
Giants are frames that are smaller than 64 bytes.
Why it's wrong here
Giants are not undersized frames; they exceed the IEEE 802.3 maximum frame size of 1518 bytes (or 1522 bytes with a VLAN tag). A frame smaller than 64 bytes is called a runt, not a giant. The confusion between the two arises because both are counted under input errors on Cisco switches, but they are opposite faults.
- ✓
Input errors include runts, giants, CRC errors, and frame errors.
Why this is correct
Cisco IOS 'show interfaces' output groups several frame-level receive faults under the 'input errors' counter. Specifically, runts (frames under 64 bytes), giants (frames over the maximum), CRC errors (failed frame check sequence), and frame errors (misaligned or non-octet-aligned frames) are all aggregated into that single statistic. This is why an engineer troubleshooting input errors must inspect the detailed breakdown to identify the real cause.
- ✗
Flaps indicate that the interface is physically disconnected.
Why it's wrong here
Flaps do not mean the interface is physically disconnected; rather, they describe a link that transitions between up and down states repeatedly over a short period. A single physical disconnection would cause one down event, not a flap. Flapping is often caused by faulty optics, marginal cabling, or duplex mismatches triggering continuous renegotiation.
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.
✓CRC errors indicate that frames were received with an invalid checksum, often due to cabling issues.Correct answer▾
Why this is correct
A CRC error means the Ethernet frame's frame check sequence (FCS) computed at the receiver does not match the value transmitted, indicating corruption during transit. This is commonly caused by faulty cabling, bad connectors, electromagnetic interference, or a marginal transceiver, rather than by a software issue. CRC errors may also be accompanied by alignment errors if the corruption shifts bit boundaries, pointing further to a physical-layer problem.
✗Runts are frames that are larger than the maximum allowed size.Wrong answer — click to see why▾
Why this is wrong here
Runts are frames smaller than 64 bytes, not larger. The minimum Ethernet frame size is 64 bytes; frames below this are considered runts and are often caused by collisions or faulty hardware.
Why candidates choose this
Students may confuse 'runts' with 'giants' due to the opposite-sounding names, or assume 'runts' refers to something undersized but incorrectly think it means oversized.
✗Giants are frames that are smaller than 64 bytes.Wrong answer — click to see why▾
Why this is wrong here
Giants are frames larger than the maximum allowed size (typically 1518 bytes without VLAN tagging), not smaller than 64 bytes. The description given is actually for runts.
Why candidates choose this
The terms 'runts' and 'giants' are easily confused because they are opposites; a student might mistakenly swap their definitions.
✗Flaps indicate that the interface is physically disconnected.Wrong answer — click to see why▾
Why this is wrong here
Flaps refer to an interface repeatedly transitioning between up and down states, not a single disconnection. A physical disconnection would show the interface as 'down' but not necessarily as a flap unless it reconnects and disconnects repeatedly.
Why candidates choose this
The term 'flap' might be interpreted as a single change in state (like a flap of a wing), but in networking it specifically implies repeated transitions.
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
Half-Duplex vs Full-Duplex
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
Key term
CRC
CRC (Cyclic Redundancy Check) is an error-detecting code used to detect accidental changes to raw data in digital networks.
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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.