The answer is to configure the interface with the `duplex full` and `speed 1000` commands under `interface GigabitEthernet0/0`. This resolves the duplex mismatch, which is the most common cause of an interface being up but the line protocol down—a classic Layer 2 issue where one side operates in full-duplex while the other uses half-duplex, corrupting frames and preventing the protocol from coming up. On the CCNA 200-301 v2 exam, this scenario tests your ability to read `show interfaces` output and identify that a mismatch, not a physical cable fault, is the root cause when the interface status shows "up/down." A common trap is to assume a Layer 1 problem or to misconfigure speed; remember that on GigabitEthernet, both sides must match—typically full-duplex—and setting speed explicitly avoids auto-negotiation failures. Memory tip: "Up/down? Duplex mismatch is the crown—check both sides, make them full, and the protocol will pull."
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Network Topology
You are troubleshooting connectivity between R1 and R2. R1's Gi0/0 interface is connected to R2's Gi0/0. R1 can ping its own IP but cannot ping R2's IP. Examine the provided 'show interfaces' output on R1 and identify the root cause. Then, apply the necessary configuration command(s) on R1 to resolve the issue.
R1# show interfaces gi0/0
GigabitEthernet0/0 is up, line protocol is down
Hardware is Gigabit Ethernet, address is aabb.cc00.0100 (bia aabb.cc00.0100)
Internet address is 192.168.1.1/30
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s, link type is auto, media type is RJ45
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
A
interface GigabitEthernet0/0
duplex full
speed 1000
This is correct because the 'line protocol is down' indicates a Layer 2 issue, often a duplex mismatch. Setting both duplex to full and speed to 1000 on R1's interface ensures consistency with R2, resolving the mismatch and bringing the line protocol up.
B
interface GigabitEthernet0/0
no shutdown
Why wrong: This is incorrect because the interface is already up (administratively up, line protocol down). The 'no shutdown' command would have no effect since the interface is not administratively down.
C
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
Why wrong: This is incorrect because the interface already has an IP address configured (R1 can ping its own IP). Reassigning the same IP does not address the Layer 2 issue causing the line protocol to be down.
D
interface GigabitEthernet0/0
no keepalive
Why wrong: This is incorrect because disabling keepalives is not a standard solution for a duplex mismatch. Keepalives are used to detect link failures; disabling them can cause other issues and does not resolve the line protocol being down due to a mismatch.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
interface GigabitEthernet0/0
duplex full
speed 1000
The 'line protocol is down' on R1's Gi0/0 interface indicates a Layer 2 issue. Since the interface is up but line protocol is down, the most common cause is a duplex mismatch or a keepalive issue. In this scenario, the interface is configured as 'full-duplex' but the far-end R2 might be set to half-duplex, causing a mismatch. The fix is to set the duplex to 'full' and speed to 1000 on R1's interface, or to use 'auto' for both. However, the correct command to resolve a duplex mismatch is to set both sides to the same setting, typically 'full' for GigabitEthernet. The command 'duplex full' under the interface will ensure R1 uses full-duplex, and if R2 is also set to full-duplex, the line protocol should come up.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 GigabitEthernet0/0
duplex full
speed 1000
Why this is correct
This is correct because the 'line protocol is down' indicates a Layer 2 issue, often a duplex mismatch. Setting both duplex to full and speed to 1000 on R1's interface ensures consistency with R2, resolving the mismatch and bringing the line protocol up.
Related concept
Read the scenario before looking for a memorised answer.
✗
interface GigabitEthernet0/0
no shutdown
Why it's wrong here
This is incorrect because the interface is already up (administratively up, line protocol down). The 'no shutdown' command would have no effect since the interface is not administratively down.
✗
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0
Why it's wrong here
This is incorrect because the interface already has an IP address configured (R1 can ping its own IP). Reassigning the same IP does not address the Layer 2 issue causing the line protocol to be down.
✗
interface GigabitEthernet0/0
no keepalive
Why it's wrong here
This is incorrect because disabling keepalives is not a standard solution for a duplex mismatch. Keepalives are used to detect link failures; disabling them can cause other issues and does not resolve the line protocol being down due to a mismatch.
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.
✓interface GigabitEthernet0/0
duplex full
speed 1000Correct answer▾
Why this is correct
This is correct because the 'line protocol is down' indicates a Layer 2 issue, often a duplex mismatch. Setting both duplex to full and speed to 1000 on R1's interface ensures consistency with R2, resolving the mismatch and bringing the line protocol up.
✗interface GigabitEthernet0/0
no shutdownWrong answer — click to see why▾
Why this is wrong here
The specific factual error is that 'no shutdown' only brings an interface out of an administratively down state, but the problem here is a line protocol issue, not an administrative shutdown.
Why candidates choose this
Candidates pick this because they see 'down' in the output and assume the interface is shut down, but the output clearly shows 'up' for the line protocol status.
✗interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.0Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the IP address is already configured correctly; the problem is at Layer 2, not Layer 3.
Why candidates choose this
Candidates pick this because they think the IP address might be missing or misconfigured, but the scenario states R1 can ping its own IP, indicating the IP is correctly assigned.
✗interface GigabitEthernet0/0
no keepaliveWrong answer — click to see why▾
Why this is wrong here
The specific factual error is that keepalive settings are not typically the cause of a line protocol down on modern Ethernet interfaces; duplex mismatch is a more common cause.
Why candidates choose this
Candidates pick this because they recall that keepalive issues can cause line protocol problems on serial interfaces, but on GigabitEthernet, this is rarely the case.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
This is incorrect because the interface is already up (administratively up, line protocol down). The 'no shutdown' command would have no effect since the interface is not administratively down.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: interface GigabitEthernet0/0
duplex full
speed 1000 — The 'line protocol is down' on R1's Gi0/0 interface indicates a Layer 2 issue. Since the interface is up but line protocol is down, the most common cause is a duplex mismatch or a keepalive issue. In this scenario, the interface is configured as 'full-duplex' but the far-end R2 might be set to half-duplex, causing a mismatch. The fix is to set the duplex to 'full' and speed to 1000 on R1's interface, or to use 'auto' for both. However, the correct command to resolve a duplex mismatch is to set both sides to the same setting, typically 'full' for GigabitEthernet. The command 'duplex full' under the interface will ensure R1 uses full-duplex, and if R2 is also set to full-duplex, the line protocol should come up.
What should I do if I get this 200-301 question wrong?
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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