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Network Infrastructure and Connectivity →hardTroubleshootingObjective-mapped

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
G0/010.0.0.1/30G0/010.0.0.2/30SFP linkR1R2

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.

Question 1hardTroubleshooting
Full question →

Exhibit

R1# show interfaces gigabitethernet 0/0
GigabitEthernet0/0 is down, line protocol is down (notconnect)
  Hardware is GigabitEthernet, address is aaaa.bbbb.cccc (bia aaaa.bbbb.cccc)
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is SFP
  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, 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 running-config interface gigabitethernet 0/0
Building configuration...

Current configuration : 85 bytes
!
interface GigabitEthernet0/0
 ip address 10.0.0.1 255.255.255.252
 speed 100
 duplex full
 negotiation auto
end

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

✓

Configure R1 with 'no speed', 'no duplex', and 'negotiation auto' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-LX SFP.

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.

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.

  • ✓

    Configure R1 with 'no speed', 'no duplex', and 'negotiation auto' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-LX SFP.

    Why this is correct

    This is correct because removing the hard-coded speed and duplex settings and enabling auto-negotiation on R1 allows the link to come up with R2. For the 5 km distance, a 1000BASE-LX SFP supports up to 10 km, meeting the requirement.

    Related concept

    Static NAT maps one inside address to one outside address.

  • ✗

    Configure R1 with 'speed 1000' and 'duplex full' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-SX SFP.

    Why it's wrong here

    This is incorrect because setting speed 1000 and duplex full on R1 while R2 is using auto-negotiation will still cause a mismatch; auto-negotiation fails when one side is hard-coded. Also, 1000BASE-SX only supports up to 550 m, insufficient for 5 km.

  • ✗

    Configure R1 with 'no speed', 'no duplex', and 'negotiation auto' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-SX SFP.

    Why it's wrong here

    This is incorrect because while the auto-negotiation fix is correct, the 1000BASE-SX SFP only supports distances up to 550 m, which is insufficient for the 5 km requirement.

  • ✗

    Configure R1 with 'speed 100' and 'duplex full' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-LX SFP.

    Why it's wrong here

    This is incorrect because setting speed 100 on a GigabitEthernet interface forces the link to 100 Mbps, which is not Gigabit Ethernet and will not work with the SFP module (which expects 1000 Mbps). Also, the hard-coded settings will cause a mismatch with R2's auto-negotiation.

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.

✓Configure R1 with 'no speed', 'no duplex', and 'negotiation auto' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-LX SFP.Correct answer▾

Why this is correct

This is correct because removing the hard-coded speed and duplex settings and enabling auto-negotiation on R1 allows the link to come up with R2. For the 5 km distance, a 1000BASE-LX SFP supports up to 10 km, meeting the requirement.

✗Configure R1 with 'speed 1000' and 'duplex full' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-SX SFP.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that hard-coding speed and duplex on one side while the other uses auto-negotiation prevents the link from coming up, and 1000BASE-SX cannot reach 5 km.

Why candidates choose this

Candidates might think that setting the same speed (1000 Mbps) will work, but they overlook the duplex mismatch issue and the distance limitation of SX.

✗Configure R1 with 'no speed', 'no duplex', and 'negotiation auto' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-SX SFP.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that 1000BASE-SX is designed for short-range multimode fiber, not long distances.

Why candidates choose this

Candidates may correctly identify the auto-negotiation issue but fail to consider the distance requirement, assuming any Gigabit SFP will work.

✗Configure R1 with 'speed 100' and 'duplex full' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-LX SFP.Wrong answer — click to see why▾

Why this is wrong here

The specific factual error is that GigabitEthernet interfaces can operate at 100 Mbps, but the SFP module requires 1000 Mbps; additionally, the speed/duplex mismatch prevents the link from coming up.

Why candidates choose this

Candidates might think that matching the original speed (100 Mbps) is necessary, but the question states the link requires Gigabit Ethernet, and the SFP module must be used at its rated speed.

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.

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.

What to study next

Got this wrong? Here's your next step.

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.

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FAQ

Questions learners often ask

What does this 200-301 question test?

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: Configure R1 with 'no speed', 'no duplex', and 'negotiation auto' on GigabitEthernet0/0, then replace the SFP module with a 1000BASE-LX SFP. — 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.

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.

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Last reviewed: Jun 6, 2026

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