JN0-106 encapsulation type Practice Question
A network engineer is troubleshooting connectivity between two directly connected Juniper routers. The interface on Router A shows 'up' but no packets are being received from Router B. Which command should the engineer use on Router A to check if the interface is expecting to receive a specific encapsulation type?
⚠ Common exam trap
Candidates often assume 'show interfaces terse' includes encapsulation details, but it only provides a quick summary. The 'extensive' option is needed for encapsulation type.
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
✓
show interfaces extensive
The 'show interfaces extensive' command displays detailed interface information, including the encapsulation type configured on the interface. If Router A expects a specific encapsulation (e.g., PPP, HDLC, or Ethernet) that does not match what Router B is sending, the interface will show 'up' but will not receive packets. This command allows the engineer to verify the configured encapsulation type. Option B is incorrect because 'show interfaces terse' provides a concise summary (name, status, protocol, and address) but does not include encapsulation details.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
show interfaces extensive
Why this is correct
The 'show interfaces extensive' command is essential because it reveals the actual data-link encapsulation currently in use on the interface, along with detailed physical and protocol state information. This allows the engineer to confirm whether both routers are configured with matching encapsulation types (e.g., PPP, HDLC, or Frame Relay). It also provides error counters and keepalive statistics, which can expose framing mismatches or negotiation failures. Without this operational view, a layer-1 connectivity issue could be mistakenly attributed to configuration when the real cause is an encapsulation mismatch.
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show interfaces terse
Why it's wrong here
The 'show interfaces terse' command outputs only a one-line summary per interface, showing administrative status, link status, and IPv4/IPv6 addresses. It deliberately omits data-link encapsulation details such as PPP or HDLC, making it unsuitable for verifying that both routers use the same encapsulation. This command is intended for a quick health check of interface state and IP addressing, not for diagnosing layer-2 framing mismatches. Relying on it here would miss the specific information needed to confirm encapsulation compatibility.
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show configuration interfaces
Why it's wrong here
The 'show configuration interfaces' command displays the configured settings for the interface from the candidate or active configuration, which might include an explicit encapsulation statement. However, it shows only the intended configuration, not the operational state or whether the encapsulation negotiation has succeeded. If the encapsulation is left at the default (e.g., HDLC on serial links), the command may not display it at all, lulling the engineer into thinking it is correct. A true verification requires the operational state shown by 'show interfaces extensive', which also exposes any mismatch between the local and remote encapsulation.
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monitor traffic interface
Why it's wrong here
The 'monitor traffic interface' command captures and displays packet data in real time, showing headers like Ethernet type or PPP protocol field, but it does not reveal the router's configured encapsulation parameter. You might see what encapsulation appears to be on the wire, but you cannot determine if the router is intentionally configured for that encapsulation or if it is a mismatch. Additionally, it is a troubleshooting tool for observing traffic flow, not a configuration inspection tool. It would not show whether the local interface's encapsulation setting matches the peer's configured setting.
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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.