The answer is to replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP on R1, then disable auto-negotiation and manually set speed to 1000 and duplex to full. This is correct because 1000BASE-T SFPs are designed for copper twisted-pair cables and cannot physically connect to a fiber-based 1000BASE-LX/LH SFP; moreover, auto-negotiation is not supported on fiber optic links and must be disabled on both ends to establish a stable connection. On the CCNA 200-301 v2 exam, this scenario tests your understanding of SFP compatibility and auto-negotiation on fiber, a common trap where candidates forget that fiber SFPs require manual configuration and matching media types. A key memory tip is “Fiber hates negotiation—always set speed 1000 and duplex full, and match the SFP to the cable type.”
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 GigabitEthernet0/0 interface is configured with a static IP of 10.0.0.1/30 but cannot ping its neighbor R2 at 10.0.0.2/30. R1 is using a 1000BASE-T SFP module to connect to a 1000BASE-LX/LH SFP on R2, but the link is down. Diagnose and resolve the issue by adjusting interface speed and duplex settings, and ensure the correct SFP is used for the 2 km fiber run.
R1# show interfaces gigabitEthernet 0/0
GigabitEthernet0/0 is down, line protocol is down
Hardware is Gigabit Ethernet, address is 0011.2233.4455 (bia 0011.2233.4455)
Internet address is 10.0.0.1/30
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)
Auto-negotiation is turned on
Full-duplex, 1000Mb/s, link type is auto, media type is SFP
output flow-control is unsupported, input flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output never, 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 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 1 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
R1# show interfaces gigabitEthernet 0/0 transceiver
Diagnostic Monitoring Information not available
R1# show run interface gigabitEthernet 0/0
Building configuration...
Current configuration : 120 bytes
!
interface GigabitEthernet0/0
ip address 10.0.0.1 255.255.255.252
speed auto
duplex auto
media-type sfp
end
R1# show interfaces gigabitEthernet 0/0 capabilities
GigabitEthernet0/0
Model: WS-C2960X-48TS-L
Type: 1000BaseLX/LH
Speed: 1000
Duplex: Full
Trunk encap. type: 802.1Q
Trunk mode: on
auto-negotiation: on
Flowcontrol: rx off,tx off
Members: 1
Link status: down
A
Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then on R1 configure 'no negotiation auto', 'speed 1000', and 'duplex full'.
This is correct because the 1000BASE-T SFP is for copper connections and cannot be used with a fiber SFP. Replacing it with a 1000BASE-LX/LH SFP matches the fiber type and distance. Disabling auto-negotiation with 'no negotiation auto' is required for fiber SFPs, and setting speed 1000 and duplex full ensures proper operation.
B
Keep the 1000BASE-T SFP and configure 'no negotiation auto', 'speed 1000', and 'duplex full' on R1.
Why wrong: This is incorrect because the 1000BASE-T SFP is designed for copper twisted-pair and cannot connect to a fiber SFP. Even with correct settings, the physical media mismatch prevents link establishment.
C
Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then configure 'speed 1000' and 'duplex full' on R1 without disabling auto-negotiation.
Why wrong: This is incorrect because fiber SFPs typically do not support auto-negotiation; leaving it enabled can cause the link to remain down. The 'no negotiation auto' command is necessary to disable it.
D
Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then configure 'no negotiation auto' on R1 without setting speed and duplex.
Why wrong: This is incorrect because even with auto-negotiation disabled, the speed and duplex must be explicitly set to 1000 and full. Without these settings, the interface may default to incorrect parameters or remain down.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then on R1 configure 'no negotiation auto', 'speed 1000', and 'duplex full'.
The link is down because auto-negotiation is enabled on R1's SFP port (which uses a 1000BASE-T SFP) while R2's port uses a 1000BASE-LX/LH SFP. Auto-negotiation must be disabled on both sides for fiber SFPs. Additionally, the 1000BASE-T SFP is for copper twisted-pair and cannot connect to a fiber SFP; it must be replaced with a 1000BASE-LX/LH SFP to match the 2 km distance. Commands to fix: on R1, 'no negotiation auto' disables auto-negotiation; 'speed 1000' and 'duplex full' set the correct parameters; then the SFP must be physically replaced with a 1000BASE-LX/LH module.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then on R1 configure 'no negotiation auto', 'speed 1000', and 'duplex full'.
Why this is correct
This is correct because the 1000BASE-T SFP is for copper connections and cannot be used with a fiber SFP. Replacing it with a 1000BASE-LX/LH SFP matches the fiber type and distance. Disabling auto-negotiation with 'no negotiation auto' is required for fiber SFPs, and setting speed 1000 and duplex full ensures proper operation.
Keep the 1000BASE-T SFP and configure 'no negotiation auto', 'speed 1000', and 'duplex full' on R1.
Why it's wrong here
This is incorrect because the 1000BASE-T SFP is designed for copper twisted-pair and cannot connect to a fiber SFP. Even with correct settings, the physical media mismatch prevents link establishment.
✗
Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then configure 'speed 1000' and 'duplex full' on R1 without disabling auto-negotiation.
Why it's wrong here
This is incorrect because fiber SFPs typically do not support auto-negotiation; leaving it enabled can cause the link to remain down. The 'no negotiation auto' command is necessary to disable it.
✗
Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then configure 'no negotiation auto' on R1 without setting speed and duplex.
Why it's wrong here
This is incorrect because even with auto-negotiation disabled, the speed and duplex must be explicitly set to 1000 and full. Without these settings, the interface may default to incorrect parameters or remain down.
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.
✓Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then on R1 configure 'no negotiation auto', 'speed 1000', and 'duplex full'.Correct answer▾
Why this is correct
This is correct because the 1000BASE-T SFP is for copper connections and cannot be used with a fiber SFP. Replacing it with a 1000BASE-LX/LH SFP matches the fiber type and distance. Disabling auto-negotiation with 'no negotiation auto' is required for fiber SFPs, and setting speed 1000 and duplex full ensures proper operation.
✗Keep the 1000BASE-T SFP and configure 'no negotiation auto', 'speed 1000', and 'duplex full' on R1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that 1000BASE-T SFPs use copper cabling and cannot interface with fiber SFPs; they are incompatible.
Why candidates choose this
Candidates pick this because they focus on the auto-negotiation issue but overlook the fundamental media mismatch between copper and fiber SFPs.
✗Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then configure 'speed 1000' and 'duplex full' on R1 without disabling auto-negotiation.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that auto-negotiation must be disabled on fiber SFPs; leaving it enabled can prevent the link from coming up.
Why candidates choose this
Candidates pick this because they correctly identify the need to replace the SFP but assume auto-negotiation can remain enabled, which is a common misconception for fiber interfaces.
✗Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then configure 'no negotiation auto' on R1 without setting speed and duplex.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that disabling auto-negotiation does not automatically set speed and duplex; they must be configured manually.
Why candidates choose this
Candidates pick this because they know auto-negotiation must be disabled but forget that speed and duplex must be explicitly configured when auto-negotiation is off.
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: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Command / output trap
This is incorrect because fiber SFPs typically do not support auto-negotiation; leaving it enabled can cause the link to remain down. The 'no negotiation auto' command is necessary to disable it.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 200-301 OSPF questions on adjacency and route selection.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Replace the 1000BASE-T SFP with a 1000BASE-LX/LH SFP, then on R1 configure 'no negotiation auto', 'speed 1000', and 'duplex full'. — The link is down because auto-negotiation is enabled on R1's SFP port (which uses a 1000BASE-T SFP) while R2's port uses a 1000BASE-LX/LH SFP. Auto-negotiation must be disabled on both sides for fiber SFPs. Additionally, the 1000BASE-T SFP is for copper twisted-pair and cannot connect to a fiber SFP; it must be replaced with a 1000BASE-LX/LH SFP to match the 2 km distance. Commands to fix: on R1, 'no negotiation auto' disables auto-negotiation; 'speed 1000' and 'duplex full' set the correct parameters; then the SFP must be physically replaced with a 1000BASE-LX/LH module.
What should I do if I get this 200-301 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 200-301 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are connected to R1 via console. The link between R1 and R2 is experiencing packet loss and CRC errors. Configure interface speed and duplex on R1's GigabitEthernet0/0 to match R2's settings, then replace the SFP module with one that supports the required 2 km distance. Finally, verify the interface is operational without errors.
hard
✓ A.Configure speed 1000, duplex full, and no negotiation auto on Gi0/0, then replace the SFP-GE-SX with SFP-GE-L.
B.Configure speed 1000 and duplex full on Gi0/0, then replace the SFP-GE-SX with SFP-GE-SX-MM.
C.Configure speed 100 and duplex full on Gi0/0, then replace the SFP-GE-SX with SFP-GE-L.
D.Configure no negotiation auto on Gi0/0, then replace the SFP-GE-SX with SFP-GE-L.
Why A: The CRC errors indicate a duplex mismatch or faulty medium. R1 is set to auto-negotiation while R2 is hardcoded to 1000/full, causing mismatch. First, set speed and duplex on R1 to match R2: 'speed 1000' and 'duplex full'. Also disable auto-negotiation with 'no negotiation auto'. The existing SFP-GE-SX only supports 550m, but the link requires 2 km; replace it with a 1000BASE-LX/LH SFP (SFP-GE-L) which supports up to 10 km. After changes, verify with 'show interfaces Gi0/0' to confirm no CRC errors and correct speed/duplex.
Last reviewed: Jun 6, 2026
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