CCNA Network Infrastructure and Connectivity Practice Question
Network Topology
You are connected to R1 via console. R1 is directly connected to R2 over a 1000BASE-T link that is failing to come up. Configure interface GigabitEthernet0/0 on R1 with the correct speed and duplex settings to match R2's configuration, and then verify the link is operational. Additionally, determine the appropriate SFP type for a new 40 km fiber link between R1 and R2.
⚠ Common exam trap
Do not assume auto-negotiation always works; when one side is hardcoded, the other must match. Also, know the distance limitations of SFP types: SX (short), LX (long, 10 km), ZX (extended, 70 km).
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 interface GigabitEthernet0/0 with 'speed 1000' and 'duplex full'. For the new fiber link, use a 1000BASE-ZX SFP.
The link is down because R1 is set to auto-negotiate speed and duplex while R2 is hardcoded to 1000 Mbps full duplex. This mismatch causes the link to fail. To fix, configure R1's GigabitEthernet0/0 with 'speed 1000' and 'duplex full'. For the new 40 km fiber link, a 1000BASE-ZX SFP is required as it supports distances up to 70 km. (1000BASE-LX supports only up to 10 km and is insufficient for 40 km.) Verify with 'show interfaces GigabitEthernet0/0' to see the link state change to up/up.
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 interface GigabitEthernet0/0 with 'speed 1000' and 'duplex full'. For the new fiber link, use a 1000BASE-ZX SFP.
Why this is correct
The interface must be explicitly set to speed 1000 and duplex full because R2 is hard-coded to those exact settings; leaving R1 on auto would disable successful negotiation and risk a duplex mismatch. Additionally, the 1000BASE-ZX SFP is specifically designed for long single-mode links, supporting distances up to 70 km, which comfortably covers the required 40 km span.
- ✗
Configure interface GigabitEthernet0/0 with 'speed auto' and 'duplex auto'. For the new fiber link, use a 1000BASE-SX SFP.
Why it's wrong here
Setting 'speed auto' and 'duplex auto' is invalid here because R2 has auto-negotiation disabled, so R1's auto settings would not detect the correct duplex and could default to half duplex, causing a severe duplex mismatch. Furthermore, 1000BASE-SX operates over multimode fiber and has a maximum reach of only 550 meters, nowhere near the required 40 km. This combination fails on both the electrical interface configuration and the optical transceiver choice.
- ✗
Configure interface GigabitEthernet0/0 with 'speed 1000' and 'duplex half'. For the new fiber link, use a 1000BASE-LX SFP.
Why it's wrong here
Gigabit Ethernet per IEEE 802.3 does not support half duplex on a point-to-point fiber link; all 1000BASE-X implementations require full duplex, so this configuration would be non-standard and the link would not initialize correctly. Even if the speed matched, the duplex mismatch with R2's full-duplex setting would produce late collisions and high error rates. Additionally, 1000BASE-LX supports up to 10 km over single-mode fiber, which is insufficient for a 40 km fiber run.
- ✗
Configure interface GigabitEthernet0/0 with 'speed 100' and 'duplex full'. For the new fiber link, use a 1000BASE-EX SFP.
Why it's wrong here
This configuration fails first because R2 is hard-coded to 1000 Mbps and will never negotiate down to 100 Mbps, so the link would not come up at the expected speed; forcing speed 100 on R1 would result in no connectivity. The choice of 1000BASE-EX also is problematic because it is not a recognized IEEE SFP standard; the appropriate long-reach optic for 40 km is 1000BASE-ZX, but it would be irrelevant given the speed mismatch. In short, the speed setting alone invalidates this option.
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 interface GigabitEthernet0/0 with 'speed 1000' and 'duplex full'. For the new fiber link, use a 1000BASE-ZX SFP.Correct answer▾
Why this is correct
The interface must be explicitly set to speed 1000 and duplex full because R2 is hard-coded to those exact settings; leaving R1 on auto would disable successful negotiation and risk a duplex mismatch. Additionally, the 1000BASE-ZX SFP is specifically designed for long single-mode links, supporting distances up to 70 km, which comfortably covers the required 40 km span.
✗Configure interface GigabitEthernet0/0 with 'speed auto' and 'duplex auto'. For the new fiber link, use a 1000BASE-SX SFP.Wrong answer — click to see why▾
Why this is wrong here
Auto-negotiation cannot match a hardcoded speed/duplex; 1000BASE-SX is for short distances (up to 550 m).
Why candidates choose this
Candidates may think auto-negotiation is always best and confuse SX (short) with long-range SFPs.
✗Configure interface GigabitEthernet0/0 with 'speed 1000' and 'duplex half'. For the new fiber link, use a 1000BASE-LX SFP.Wrong answer — click to see why▾
Why this is wrong here
Gigabit Ethernet does not support half duplex; 1000BASE-LX maximum distance is 10 km.
Why candidates choose this
Candidates may think half duplex is acceptable or that LX can be extended beyond its standard range.
✗Configure interface GigabitEthernet0/0 with 'speed 100' and 'duplex full'. For the new fiber link, use a 1000BASE-EX SFP.Wrong answer — click to see why▾
Why this is wrong here
Speed mismatch (100 vs 1000) will cause link failure; 1000BASE-EX is not an IEEE standard (ZX is used for extended reach).
Why candidates choose this
Candidates may confuse EX with extended reach or think a lower speed might work.
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?”
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
Half-Duplex vs Full-Duplex
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
Key term
Full duplex
Full duplex is a communication mode where data can be sent and received simultaneously between two parties, like a two-way conversation without interruptions.
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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.