CCNA Network Infrastructure and Connectivity Practice Question
A network engineer notices that after issuing the no shutdown command on interface GigabitEthernet0/0 of a router, the interface remains down. The output of show interfaces GigabitEthernet0/0 displays 'GigabitEthernet0/0 is down, line protocol is down'. The physically connected switch port is also administratively down. What is the most likely cause?
⚠ Common exam trap
Cisco does test the distinction between local and remote administrative shutdown, but the resulting state would be 'down/down', not 'up/down'. Students should understand that 'up/down' implies Layer 1 is functional, which cannot happen if the remote port is shut down.
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
✓
The connected switch port is administratively down.
The output 'GigabitEthernet0/0 is down, line protocol is down' indicates that both Layer 1 and Layer 2 are down. Since the directly connected switch port is administratively down, the router interface detects no carrier and remains down/down even after the local no shutdown command. Therefore, option A is the most likely cause.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The connected switch port is administratively down.
Why this is correct
An administratively down switch port is placed in the shutdown state, which disables all physical-layer signaling and removes carrier from the cable. The router consequently senses no layer 1 presence on its interface, so the line protocol cannot transition to up even if the router's own configuration is otherwise sound. This is the direct and definitive cause of the line protocol being down, as no handshake or frame exchange can occur.
- ✗
Mismatched encapsulation types on the router and switch.
Why it's wrong here
A mismatched encapsulation (e.g., IEEE 802.1Q on the switch and ISL on the router, or one side set to dot1q while the other uses a native untagged configuration) only becomes relevant when both ends of a trunk link are active and attempting to negotiate or interpret VLAN tagging. Since the switch port is administratively down, it sends no frames, no DTP, and no encapsulation-related signaling; thus the router's line protocol fails before any encapsulation negotiation could ever take place. It is a possible secondary issue only if the port were operational, but it is not the root cause in this scenario.
- ✗
Speed and duplex mismatch between the router and switch.
Why it's wrong here
Speed and duplex mismatches usually manifest as excessive CRC errors, late collisions, or a link that flaps after auto-negotiation completes, yet they require both interfaces to be actively transmitting link pulses. With the switch port shut down, there is no physical link at all, so the router can never establish even a basic carrier detect, which is essential for the line protocol to come up. Therefore, while a mismatch could degrade an already-up link, it cannot explain a line protocol that remains down when the adjacent switch port is administratively disabled.
- ✗
Incorrect native VLAN configuration on the trunk link.
Why it's wrong here
A native VLAN mismatch on a trunk link can cause line protocol issues, but there is no indication that the link is a trunk, and the switch port being administratively down is a more direct cause.
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.
✓The connected switch port is administratively down.Correct answer▾
Why this is correct
An administratively down switch port is placed in the shutdown state, which disables all physical-layer signaling and removes carrier from the cable. The router consequently senses no layer 1 presence on its interface, so the line protocol cannot transition to up even if the router's own configuration is otherwise sound. This is the direct and definitive cause of the line protocol being down, as no handshake or frame exchange can occur.
✗Mismatched encapsulation types on the router and switch.Wrong answer — click to see why▾
Why this is wrong here
Candidates often attribute line protocol down to encapsulation issues, missing the clear indication that the switch port is shut down.
✗Speed and duplex mismatch between the router and switch.Wrong answer — click to see why▾
Why this is wrong here
Duplex mismatch is a common cause of interface issues, so candidates may assume it without considering the explicitly stated admin-down condition.
✗Incorrect native VLAN configuration on the trunk link.Wrong answer — click to see why▾
Why this is wrong here
Candidates may recall VLAN mismatch as a cause for line protocol down on trunk links, forgetting that the scenario gives a clear admin-down state.
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?”
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Troubleshoot: Switch Interface Down
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An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
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An ISP is a company that provides individuals and organizations access to the Internet, along with related services like email and web hosting.
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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.