Diagnosing Router Interface Output Drops as Oversubscription

Identify interface and cable issues (collisions, errors, mismatch duplex, and/or speed)
Answer Correct answer: C — The huge 'Total output drops' counter means the interface cannot forward the offered load, indicating port oversubscription, not a CRC or duplex fault.

Refer to the exhibit. What is the cause of poor performance on router R19? - image

  1. excessive collisions
  2. excessive CRC errors
  3. port oversubscription Correct Answer
  4. speed and duplex mismatch

Community Votes

C
75%
D
25%

75% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Community Insight

Output drops = egress congestion/oversubscription. CRC errors and speed/duplex mismatch show up as input/CRC errors, not as output drops.

In a 'show interface' output, a massive Total output drops count (here 135M) shows the egress interface is overloaded — more traffic offered than it can transmit. Collisions and CRC errors, if present, are minor by comparison. Speed/duplex mismatch typically shows as CRC/input errors, not output drops.

Picking D (speed/duplex mismatch): that causes CRC and input errors, not output drops. The dominant signal here is the enormous output-drop counter.

Community Discussion (4 comments)

SnowWhiteYeti 👍 5 Selected: C
The key indicator in the output is the "Total output drops: 135298429". This suggests a significant number of packets are being dropped because the interface cannot handle the traffic, which is typically due to port oversubscription (answer C). While there are some CRC errors and collisions, these numbers are much smaller compared to the massive number of output drops, which points toward the port being overwhelmed with traffic, a classic sign of oversubscription rather than issues like collisions or CRC errors. So the correct answer is C. port oversubscription.
bezkin 👍 1
this output was taken after they were finished pushing the traffic, i believe thats why we dont see anything in the output queue (if it were happening in realtime, we would see the output queue max out as well to give more indication) which is somewhat fair, sometimes when we investigate an issue, it isnt happening in realtime anymore, but we still need to solve it.
exiledwl 👍 1 Selected: C
snowwhiteyeti comment seems legit
Gene_nstudy 👍 2 Selected: D
This show interface output is strange.

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Expert Analysis

Why the Answer Is Correct

C is correct. The key indicator is 'Total output drops: 135298429' — vastly larger than the collision/CRC counts — which points to egress congestion because the interface cannot handle the offered traffic (port oversubscription).

Why the Other Options Are Wrong

A (excessive collisions) and B (excessive CRC errors) are present but tiny next to the output-drop figure. D (speed/duplex mismatch) would manifest as CRC/input errors rather than output drops.

Community Comment Notes

The vote is C (75) versus D (25). The leading comment highlights 'Total output drops: 135298429' as the signal of oversubscription, noting CRC/collision numbers are comparatively small.

Official Reference

https://learningnetwork.cisco.com/s/ccna-exam-topics

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