CCNA Network Infrastructure and Connectivity Practice Question
Network Topology
You are connected to R1. Configure IPv4 and IPv6 addressing on R1's interfaces so that R1 can reach R2's loopback0 (192.0.2.1/32) and R2's IPv6 loopback0 (2001:db8:1::1/64). R1 has a misconfigured subnet mask on G0/0 and is missing its default gateway. Additionally, R1 has a duplicate IPv4 address on G0/1 that must be corrected. Use EUI-64 for R1's IPv6 link-local address on G0/0 and static IPv6 for the global unicast address on G0/1.
⚠ Common exam trap
Watch out for common mistakes: using the wrong subnet mask (e.g., /24 instead of /30), pointing the default gateway to the wrong next-hop (e.g., 10.0.0.1 instead of 10.0.0.2), and failing to resolve duplicate IPs by moving to a different subnet. Also, ensure IPv6 addresses are unique and not conflicting with other devices.
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
✓
Change G0/0 mask to /30, add default route via 10.0.0.2, change G0/1 IP to 192.0.2.2/30, enable IPv6 on G0/0 with EUI-64 link-local, assign 2001:db8:2::1/64 to G0/1
Ly fixes the subnet mask on G0/0 to /30, adds the default gateway via 10.0.0.2, resolves the duplicate IP on G0/1 by assigning 192.0.2.2/30, and sets up IPv6 addressing as required (EUI-64 on G0/0 and static 2001:db8:2::1/64 on G0/1). However, for full IPv6 reachability to R2's loopback0 (2001:db8:1::1/64), R1 also needs an IPv6 route (e.g., a static route to 2001:db8:1::/64 via R2's link-local or global address on G0/1). Without this, Option A only ensures IPv4 connectivity but not IPv6. Among the given options, A is the best because it addresses all IPv4 issues and the IPv6 addressing requirements, though it is incomplete for IPv6 routing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Change G0/0 mask to /30, add default route via 10.0.0.2, change G0/1 IP to 192.0.2.2/30, enable IPv6 on G0/0 with EUI-64 link-local, assign 2001:db8:2::1/64 to G0/1
Why this is correct
Ly fixes all issues: the subnet mask on G0/0 is changed to /30 to match the connected network, a default route via 10.0.0.2 provides a gateway to reach R2's loopbacks, G0/1 gets a unique IP (192.0.2.2/30) to resolve the duplicate, IPv6 is enabled on G0/0 with EUI-64 for link-local, and G0/1 gets a static global unicast address (2001:db8:2::1/64) as required.
- ✗
Change G0/0 mask to /24, add default route via 10.0.0.1, change G0/1 IP to 10.0.0.6/30, enable IPv6 on G0/0 with EUI-64 link-local, assign 2001:db8:1::1/64 to G0/1
Why it's wrong here
This is incorrect because changing G0/0 mask to /24 does not match the /30 subnet used by R2, so R1 cannot communicate with R2's G0/0. The default route via 10.0.0.1 is not the correct next-hop (should be 10.0.0.2). Changing G0/1 to 10.0.0.6/30 still conflicts with R2's G0/1 (10.0.0.5/30) because 10.0.0.6 is in the same subnet. Assigning 2001:db8:1::1/64 to G0/1 duplicates R2's loopback address.
- ✗
Change G0/0 mask to /30, add default route via 10.0.0.1, change G0/1 IP to 192.0.2.2/30, enable IPv6 on G0/0 with EUI-64 link-local, assign 2001:db8:2::1/64 to G0/1
Why it's wrong here
This is incorrect because the default route should point to 10.0.0.2, not 10.0.0.1. R2's G0/0 IP is 10.0.0.2, so the next-hop must be 10.0.0.2. Using 10.0.0.1 as the gateway would send traffic to an incorrect or non-existent neighbor.
- ✗
Change G0/0 mask to /30, add default route via 10.0.0.2, change G0/1 IP to 10.0.0.6/30, enable IPv6 on G0/0 with EUI-64 link-local, assign 2001:db8:2::1/64 to G0/1
Why it's wrong here
This is incorrect because changing G0/1 to 10.0.0.6/30 still conflicts with R2's G0/1 (10.0.0.5/30). Both addresses are in the same /30 subnet (10.0.0.4/30), causing a duplicate IP issue. The correct action is to assign an IP from a different subnet, such as 192.0.2.2/30.
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.
✓Change G0/0 mask to /30, add default route via 10.0.0.2, change G0/1 IP to 192.0.2.2/30, enable IPv6 on G0/0 with EUI-64 link-local, assign 2001:db8:2::1/64 to G0/1Correct answer▾
Why this is correct
Ly fixes all issues: the subnet mask on G0/0 is changed to /30 to match the connected network, a default route via 10.0.0.2 provides a gateway to reach R2's loopbacks, G0/1 gets a unique IP (192.0.2.2/30) to resolve the duplicate, IPv6 is enabled on G0/0 with EUI-64 for link-local, and G0/1 gets a static global unicast address (2001:db8:2::1/64) as required.
✗Change G0/0 mask to /24, add default route via 10.0.0.1, change G0/1 IP to 10.0.0.6/30, enable IPv6 on G0/0 with EUI-64 link-local, assign 2001:db8:1::1/64 to G0/1Wrong answer — click to see why▾
Why this is wrong here
The subnet mask on G0/0 must match the connected network (/30), not /24. The default gateway should point to the neighbor's IP (10.0.0.2). The new G0/1 IP must be in a different subnet to avoid duplication. The IPv6 global unicast address on G0/1 must be unique and not conflict with R2's loopback.
Why candidates choose this
Candidates might think /24 is a common mask and that 10.0.0.1 is a typical gateway. They may also mistakenly believe that 10.0.0.6/30 is different from 10.0.0.5/30, not realizing they are in the same subnet. Using 2001:db8:1::1/64 might seem like a valid global unicast address but it duplicates R2's loopback.
✗Change G0/0 mask to /30, add default route via 10.0.0.1, change G0/1 IP to 192.0.2.2/30, enable IPv6 on G0/0 with EUI-64 link-local, assign 2001:db8:2::1/64 to G0/1Wrong answer — click to see why▾
Why this is wrong here
The default gateway must be the IP address of the directly connected neighbor (R2's G0/0), which is 10.0.0.2, not 10.0.0.1.
Why candidates choose this
Candidates often assume the default gateway is the first usable IP in the subnet (10.0.0.1) without verifying the actual neighbor's IP. They may also confuse the router's own IP with the gateway.
✗Change G0/0 mask to /30, add default route via 10.0.0.2, change G0/1 IP to 10.0.0.6/30, enable IPv6 on G0/0 with EUI-64 link-local, assign 2001:db8:2::1/64 to G0/1Wrong answer — click to see why▾
Why this is wrong here
The IP address 10.0.0.6/30 is in the same subnet as R2's G0/1 (10.0.0.5/30), so it does not resolve the duplicate address conflict. A different subnet must be used.
Why candidates choose this
Candidates might think that 10.0.0.6 is different from 10.0.0.5 and therefore not a duplicate, but they overlook that both are in the same /30 subnet. They may also assume that using a different host ID within the same subnet is sufficient.
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
IPv4 Address Class Summary
| Class | First Octet Range | Default Mask | Networks | Hosts per Network |
|---|---|---|---|---|
| A | 1–126 | /8 (255.0.0.0) | 126 | 16,777,214 |
| B | 128–191 | /16 (255.255.0.0) | 16,384 | 65,534 |
| C | 192–223 | /24 (255.255.255.0) | 2,097,152 | 254 |
| D | 224–239 | N/A | Multicast groups | — |
| E | 240–255 | N/A | Reserved / experimental | — |
127.x.x.x is reserved for loopback. Modern networks use CIDR (classless) rather than classful addressing.
Go deeper
Related to this question
Learn chapter
IPv4 Addressing and Address Classes
Key term
IPv4
IPv4 is the fourth version of the Internet Protocol, a set of rules that assigns unique numerical addresses to devices so they can communicate over networks like the internet.
Key term
CAN
A CAN (Controller Area Network) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other without a host computer.
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JA
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.