Interface Flapping: Faulty SFP Module as Cause
Exhibit
Refer to the exhibit. Oct 10 10:00:00 router mgd[1234]: UI_COMMIT: User 'admin' requested commit Oct 10 10:00:05 router mgd[1234]: UI_COMMIT_PROGRESS: Commit operation in progress Oct 10 10:00:10 router mib2d[5678]: SNMP_TRAP_LINK_DOWN: ifIndex 5, ifDescr ge-0/0/1 Oct 10 10:00:11 router mib2d[5678]: SNMP_TRAP_LINK_UP: ifIndex 5, ifDescr ge-0/0/1 Oct 10 10:00:15 router kernel: interface ge-0/0/1 link up Oct 10 10:00:20 router kernel: interface ge-0/0/1 link down Oct 10 10:00:25 router kernel: interface ge-0/0/1 link up Sep 20 09:00:00 router mgd[1234]: UI_COMMIT: User 'config' requested commit
Refer to the exhibit. Based on the log output, what is the most likely issue with interface ge-0/0/1?
⚠ Common exam trap
Many candidates assume any interface issue is configuration-related (Option D) or that a single 'link UP' message means the interface is stable (Option B), but the repeated pattern of alternating UP/DOWN events is the definitive indicator of flapping.
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
✓
Interface is experiencing flapping
The log output shows repeated 'link UP' and 'link DOWN' events for interface ge-0/0/1 within a short time window, which is the classic symptom of interface flapping. Flapping typically occurs due to physical layer issues such as faulty cables, damaged transceivers, or marginal signal integrity, causing the interface to continuously transition between up and down states.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Interface is experiencing flapping
Why this is correct
The log output shows repeated interface state transitions between up and down within a short time window, which is the classic signature of interface flapping. Such behavior is typically caused by physical-layer issues, such as a faulty transceiver, damaged cable, or a remote peer that is itself unstable. An interface that is flapping never reaches a sustained operational state, so the up/down cycles evident in the log directly support this conclusion.
- ✗
Interface is up and stable
Why it's wrong here
If the interface were truly up and stable, the log would show a single link-up event followed by no subsequent state changes. Instead, the log records multiple down and up transitions, which indicates ongoing instability rather than a steady operational link. A stable interface would not exhibit repeated link-down events after the initial activation, so this option contradicts the observed log output.
- ✗
Interface is administratively down
Why it's wrong here
An administratively down interface would remain disabled until an operator issues the 'no shutdown' command, producing a 'administratively down' status and not spontaneous recovery. The log does not show an administrative disable event; rather, it shows the interface repeatedly toggling between physical up and down states. This pattern is consistent with flapping caused by external link conditions, not with a single administrative shutdown.
- ✗
Interface is configured incorrectly
Why it's wrong here
Configuration errors typically generate syslog messages during commit or validation, such as syntax errors or invalid parameter warnings, and would not cause repeated interface state transitions. The log only contains link up/down events, which point to a physical or line-protocol issue rather than a configuration problem. While a misconfiguration could lead to protocol-level instability, it would not produce the alternating link states seen here without accompanying configuration-error logs.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
Go deeper
Related to this question
About these practice questions
This JN0-106 question is part of Courseiva's 326-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 practice question is part of Courseiva's free Juniper Networks 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 JN0-106 exam.