XK0-004 · Question #248
A user is reporting unusual slowness when trying to transfer a large file to an NFS server from a workstation. The administrator runs tracepath and gets the following output: Which of the following…
The correct answer is A. The path MTU is lower than the source MTU. Reduce the source MTU setting. The tracepath output shows a reduced MTU at an intermediate hop, meaning the path MTU is smaller than the source MTU, causing packet fragmentation that degrades large NFS file transfers.
Question
A user is reporting unusual slowness when trying to transfer a large file to an NFS server from a workstation. The administrator runs tracepath and gets the following output:
Which of the following BEST describes the issue and a possible solution?
Exhibit
Options
- AThe path MTU is lower than the source MTU. Reduce the source MTU setting.
- BThere is latency at the storage device. Work with the storage team to correct the issue.
- CThere is latency on an intermediate router. Increase the path MTU to compensate.
- DThere are dropped packets at an intermediate router. Work with the network team to correct the
How the community answered
(29 responses)- A66% (19)
- B10% (3)
- C21% (6)
- D3% (1)
Why each option
The tracepath output shows a reduced MTU at an intermediate hop, meaning the path MTU is smaller than the source MTU, causing packet fragmentation that degrades large NFS file transfers.
tracepath probes each hop along the route and reports the discovered path MTU. When a hop reports a smaller MTU than the source interface MTU, large packets are fragmented or silently dropped, creating severe overhead on bulk transfers like NFS. Lowering the source MTU to match the discovered path MTU eliminates fragmentation and restores throughput.
tracepath measures per-hop round-trip time and MTU discovery, not storage device I/O latency - the output reflects a network-layer MTU constraint, not a storage performance problem.
The path MTU is determined by the most restrictive link along the route and cannot be unilaterally increased from the client; the correct fix is to reduce the source MTU to fit within that constraint.
tracepath output showing a reduced MTU at a hop indicates a configuration mismatch, not packet drops - dropped packets would show as asterisks or no response, not a lower MTU value.
Concept tested: Path MTU discovery and network performance troubleshooting
Source: https://man7.org/linux/man-pages/man8/tracepath.8.html
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