The correct answer is to replace the SFP with a 1000BASE-LX, disable auto-negotiation with the no negotiation auto command, and remove any manually configured speed 1000 and duplex full statements. This is because fiber link configuration requires matching the SFP type to the distance—1000BASE-SX only supports 550 meters, while 1000BASE-LX handles up to 10 km, making it the proper SFP type for a 2 km link. On fiber SFPs, auto-negotiation is not supported; the interface must rely on fixed 1000 Mbps full-duplex defaults, so disabling negotiation and removing redundant speed/duplex commands is essential for the link to come up. On the CCNA 200-301 v2 exam, this scenario tests your understanding of fiber optic standards and the fact that auto-negotiation is a copper-only feature—a common trap is leaving negotiation auto enabled or choosing an SFP based on connector type rather than wavelength and distance. Memory tip: For fiber, remember “LX for Long, SX for Short,” and always disable negotiation on fiber links.
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 connected to R1 via the console. R1 and R2 are connected via a fiber link using SFPs. The link is not coming up. Configure the correct SFP type on R1's interface GigabitEthernet0/0 to support the required 2 km distance, and fix any auto-negotiation or speed/duplex misconfiguration so that the link becomes operational.
R1# show running-config interface gigabitEthernet 0/0
Building configuration...
Current configuration : 105 bytes
!
interface GigabitEthernet0/0
ip address 10.0.0.1 255.255.255.252
duplex full
speed 1000
negotiation auto
end
R1# show interfaces gigabitEthernet 0/0
GigabitEthernet0/0 is down, line protocol is down (notconnect)
Hardware is ISR4331, address is aaaa.bbbb.cccc (bia aaaa.bbbb.cccc)
Description: Link to R2
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)
Full-duplex, 1000Mb/s, link type is auto, media type is SX
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 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
R1# show interfaces gigabitEthernet 0/0 transceiver properties
Diagnostic Monitoring is not available
R1# show interfaces gigabitEthernet 0/0 transceiver detail
GigabitEthernet0/0: transceiver module is SFP, type is SX
Name: CISCO-AVAGO
Part number: FTLC1151RDPL-C1
Revision: A0
Serial number: FNS1234567
Nominal bitrate: 1000 Mbit/sec
Wavelength: 850 nm
Distance: 550 m
Link length supported for 50/125µm OM3 fiber: 550 m
Link length supported for 62.5/125µm OM2 fiber: 300 m
Temperature: 35 degrees C
Voltage: 3.3 V
Current: 8.0 mA
Optical output power: -3.0 dBm
Optical input power: -40.0 dBm (low, indicates no light from remote)
Laser bias current: 8.0 mA
Laser temperature: 35 degrees C
R1# show logging | include GigabitEthernet0/0
*Mar 1 00:01:23.456: %LINK-3-UPDOWN: Interface GigabitEthernet0/0, changed state to down
*Mar 1 00:01:24.456: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to down
*Mar 1 00:02:10.789: %PHY-4-UNSUPPORTED_TRANSCEIVER: Unsupported or incompatible transceiver detected in interface GigabitEthernet0/0
*Mar 1 00:02:15.123: %PHY-4-UNSUPPORTED_TRANSCEIVER: Unsupported or incompatible transceiver detected in interface GigabitEthernet0/0
*Mar 1 00:02:20.456: %PHY-4-UNSUPPORTED_TRANSCEIVER: Unsupported or incompatible transceiver detected in interface GigabitEthernet0/0
A
Replace SFP with 1000BASE-LX, configure 'no negotiation auto' on GigabitEthernet0/0, and remove 'speed 1000' and 'duplex full'.
1000BASE-LX (1310 nm) supports distances up to 10 km, meeting the 2 km requirement. Fiber SFPs do not use auto-negotiation; 'no negotiation auto' disables it. Speed and duplex are fixed by the SFP standard, so explicit commands are unnecessary and may cause issues.
B
Replace SFP with 1000BASE-SX, configure 'negotiation auto' on GigabitEthernet0/0, and keep 'speed 1000' and 'duplex full'.
Why wrong: 1000BASE-SX (850 nm) only supports up to 550 meters, insufficient for 2 km. Auto-negotiation is not used on fiber links; it should be disabled. Keeping speed/duplex commands is unnecessary but not harmful.
C
Replace SFP with 1000BASE-LX, configure 'negotiation auto' on GigabitEthernet0/0, and keep 'speed 1000' and 'duplex full'.
Why wrong: While the SFP type is correct, fiber links do not support auto-negotiation; 'negotiation auto' can cause the interface to fail to come up. The speed and duplex commands are unnecessary but not incorrect.
D
Replace SFP with 1000BASE-LX, configure 'no negotiation auto' on GigabitEthernet0/0, and configure 'speed 100' and 'duplex full'.
Why wrong: This option correctly replaces the SFP and disables auto-negotiation, but keeping 'speed 1000' and 'duplex full' is unnecessary. While not strictly wrong, it is not the cleanest configuration; however, the question asks to 'fix any auto-negotiation or speed/duplex misconfiguration', implying removal of unnecessary commands. More importantly, the correct answer explicitly removes them, making this option less correct.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Replace SFP with 1000BASE-LX, configure 'no negotiation auto' on GigabitEthernet0/0, and remove 'speed 1000' and 'duplex full'.
The current SFP is 1000BASE-SX (850 nm), rated for only 550 m, which is insufficient for a 2 km link. It must be replaced with a 1000BASE-LX SFP that supports up to 10 km. The interface currently has 'speed 1000', 'duplex full', and 'negotiation auto'. On fiber SFPs, auto-negotiation is not supported and the speed and duplex are fixed at 1000 Mbps full duplex; therefore, 'no negotiation auto' is required, and any manually configured speed/duplex that violates the SFP's capabilities will prevent the link from coming up. Option A correctly uses 1000BASE-LX, disables auto-negotiation, and removes the redundant speed/duplex commands (the defaults are sufficient). Option D incorrectly sets 'speed 100', which is incompatible with the 1000BASE-LX SFP, causing the link to fail. Option B uses the wrong SFP type (1000BASE-SX). Option C uses the correct SFP but leaves 'negotiation auto', which is unsupported on fiber SFPs and will keep the link down.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 SFP with 1000BASE-LX, configure 'no negotiation auto' on GigabitEthernet0/0, and remove 'speed 1000' and 'duplex full'.
Why this is correct
1000BASE-LX (1310 nm) supports distances up to 10 km, meeting the 2 km requirement. Fiber SFPs do not use auto-negotiation; 'no negotiation auto' disables it. Speed and duplex are fixed by the SFP standard, so explicit commands are unnecessary and may cause issues.
Related concept
Static NAT maps one inside address to one outside address.
✗
Replace SFP with 1000BASE-SX, configure 'negotiation auto' on GigabitEthernet0/0, and keep 'speed 1000' and 'duplex full'.
Why it's wrong here
1000BASE-SX (850 nm) only supports up to 550 meters, insufficient for 2 km. Auto-negotiation is not used on fiber links; it should be disabled. Keeping speed/duplex commands is unnecessary but not harmful.
✗
Replace SFP with 1000BASE-LX, configure 'negotiation auto' on GigabitEthernet0/0, and keep 'speed 1000' and 'duplex full'.
Why it's wrong here
While the SFP type is correct, fiber links do not support auto-negotiation; 'negotiation auto' can cause the interface to fail to come up. The speed and duplex commands are unnecessary but not incorrect.
✗
Replace SFP with 1000BASE-LX, configure 'no negotiation auto' on GigabitEthernet0/0, and configure 'speed 100' and 'duplex full'.
Why it's wrong here
This option correctly replaces the SFP and disables auto-negotiation, but keeping 'speed 1000' and 'duplex full' is unnecessary. While not strictly wrong, it is not the cleanest configuration; however, the question asks to 'fix any auto-negotiation or speed/duplex misconfiguration', implying removal of unnecessary commands. More importantly, the correct answer explicitly removes them, making this option less correct.
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 SFP with 1000BASE-LX, configure 'no negotiation auto' on GigabitEthernet0/0, and remove 'speed 1000' and 'duplex full'.Correct answer▾
Why this is correct
1000BASE-LX (1310 nm) supports distances up to 10 km, meeting the 2 km requirement. Fiber SFPs do not use auto-negotiation; 'no negotiation auto' disables it. Speed and duplex are fixed by the SFP standard, so explicit commands are unnecessary and may cause issues.
✗Replace SFP with 1000BASE-SX, configure 'negotiation auto' on GigabitEthernet0/0, and keep 'speed 1000' and 'duplex full'.Wrong answer — click to see why▾
Why this is wrong here
The SFP type is incorrect for the distance; 1000BASE-SX cannot reach 2 km.
Why candidates choose this
Candidates may think SX is standard for short distances and assume auto-negotiation is always required.
✗Replace SFP with 1000BASE-LX, configure 'negotiation auto' on GigabitEthernet0/0, and keep 'speed 1000' and 'duplex full'.Wrong answer — click to see why▾
Why this is wrong here
Auto-negotiation is not supported on fiber interfaces; it should be disabled with 'no negotiation auto'.
Why candidates choose this
Candidates may believe auto-negotiation is needed for all Ethernet links, not realizing fiber SFPs have fixed parameters.
✗Replace SFP with 1000BASE-LX, configure 'no negotiation auto' on GigabitEthernet0/0, and configure 'speed 100' and 'duplex full'.Wrong answer — click to see why▾
Why this is wrong here
Setting 'speed 100' on a 1000BASE-LX SFP is invalid because the SFP only operates at 1000 Mbps; the link will not come up.
Why candidates choose this
Candidates may think keeping speed/duplex is harmless, but the question expects a clean configuration that removes misconfigurations.
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: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Trap categories for this question
Command / output trap
1000BASE-SX (850 nm) only supports up to 550 meters, insufficient for 2 km. Auto-negotiation is not used on fiber links; it should be disabled. Keeping speed/duplex commands is unnecessary but not harmful.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-301 NAT questions on configuration and troubleshooting.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Replace SFP with 1000BASE-LX, configure 'no negotiation auto' on GigabitEthernet0/0, and remove 'speed 1000' and 'duplex full'. — The current SFP is 1000BASE-SX (850 nm), rated for only 550 m, which is insufficient for a 2 km link. It must be replaced with a 1000BASE-LX SFP that supports up to 10 km. The interface currently has 'speed 1000', 'duplex full', and 'negotiation auto'. On fiber SFPs, auto-negotiation is not supported and the speed and duplex are fixed at 1000 Mbps full duplex; therefore, 'no negotiation auto' is required, and any manually configured speed/duplex that violates the SFP's capabilities will prevent the link from coming up. Option A correctly uses 1000BASE-LX, disables auto-negotiation, and removes the redundant speed/duplex commands (the defaults are sufficient). Option D incorrectly sets 'speed 100', which is incompatible with the 1000BASE-LX SFP, causing the link to fail. Option B uses the wrong SFP type (1000BASE-SX). Option C uses the correct SFP but leaves 'negotiation auto', which is unsupported on fiber SFPs and will keep the link down.
What should I do if I get this 200-301 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-301 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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 the console. R1 and R2 are directly connected via their GigabitEthernet0/0 interfaces. The link between them is down. Your task is to diagnose and fix the issue: R1's interface is configured for 100 Mbps full-duplex, but R2 is using auto-negotiation. Additionally, the link requires a Gigabit Ethernet connection over a distance of 5 km. Configure R1's interface to match R2's settings (auto-negotiation) and then select and install the correct SFP module to support the 5 km distance requirement.
hard
✓ A.Configure R1 with 'no speed', 'no duplex', and 'negotiation auto' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-LX SFP.
B.Configure R1 with 'speed 1000' and 'duplex full' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-SX SFP.
C.Configure R1 with 'no speed', 'no duplex', and 'negotiation auto' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-SX SFP.
D.Configure R1 with 'speed 100' and 'duplex full' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-LX SFP.
Why A: The link is down because R1 is forcing speed 100 and full-duplex while R2 is using auto-negotiation. When one side is hard-coded and the other is set to auto, auto-negotiation fails and the link does not come up. The fix is to enable auto-negotiation on R1 by removing the manual speed and duplex settings with the 'no speed' and 'no duplex' commands, and then using 'negotiation auto'. For the 5 km distance, a standard 1000BASE-SX SFP (550 m) is insufficient; a 1000BASE-LX SFP (up to 10 km) is required. The candidate must also replace the SFP module with a compatible LX SFP.
Variation 2. You are connected to R1 via console. R1's GigabitEthernet0/1 interface connects to a remote site switch over a 2 km fiber link. The current configuration shows speed and duplex set to 1000 Mbps and full, but the interface is down/down due to an SFP mismatch. Review the exhibit, identify the problem, and correct it so that the interface comes up and communicates at the correct speed and duplex. Additionally, ensure the interface is configured to auto-negotiate properly for future cable replacements.
hard
✓ A.Replace the SFP with a 1000BASE-LX module, remove the manual speed and duplex settings, and issue the no shutdown command.
B.Replace the SFP with a 1000BASE-SX module, keep the manual speed 1000 and duplex full, and issue the no shutdown command.
C.Keep the existing SFP, change the speed to 100 and duplex to half, and issue the no shutdown command.
D.Replace the SFP with a 1000BASE-LX module, keep the manual speed 1000 and duplex full, and issue the no shutdown command.
Why A: The interface was administratively shut down (shutdown command) and had hard-coded speed 1000 and duplex full, which is incompatible with the 2 km fiber link requiring a long-haul SFP (e.g., 1000BASE-LX). The correct fix is to remove the manual speed/duplex settings, enable auto-negotiation (which is default but overridden), and then no shutdown. For a 2 km link, a 1000BASE-LX SFP is required; the existing SFP (likely 1000BASE-SX, max 550 m) caused the link to be down. After replacing with the correct SFP, the interface should come up. Commands: interface Gi0/1, no speed, no duplex, no shutdown.
Last reviewed: Jun 6, 2026
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