CCNA Network Infrastructure and Connectivity Practice Question
Network Topology
You are connected to R1. Configure IPv4 and IPv6 addressing on interfaces G0/0 and G0/1 so that R1 can reach R2's loopback0 (198.51.100.1/32) and R2 can reach R1's loopback0 (203.0.113.1/32). The current configuration has a wrong subnet mask on R1 G0/0 and a missing default gateway on R2, causing reachability failures. Additionally, configure IPv6 using EUI-64 on R1 G0/1 and static IPv6 on R2 G0/1 to enable IPv6 ping between the two routers. All devices are routers.
⚠ Common exam trap
Watch for subnet mask mismatches on point-to-point links; both ends must use the same mask. Also, ensure default routes point to the correct next-hop IP (the neighbor's interface IP). For IPv6, both interfaces must be on the same subnet to communicate directly.
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
✓
On R1 G0/0, change subnet mask to 255.255.255.252; on R2, add ip route 0.0.0.0 0.0.0.0 10.0.0.1; for IPv6, on R2 G0/1 change address to 2001:db8:1::2/64.
The primary IPv4 issues are a subnet mask mismatch on the point-to-point link and a missing default gateway on R2. On R1 G0/0, the mask is /24 instead of /30; while both routers can reach each other directly, the mismatched subnet mask causes routing inconsistencies because R1 advertises the link as a /24, potentially affecting routing decisions. Fixing the mask to /30 ensures both routers agree on the subnet. R2 lacks a route to R1's loopback and the 192.168.1.0/24 network, so a default route via 10.0.0.1 resolves reachability. For IPv6, R1 G0/1 uses EUI-64, and R2 G0/1 must be on the same subnet (2001:db8:1::/64); R2's address was incorrectly set to 2001:db8:2::2/64, so changing it to 2001:db8:1::2/64 enables IPv6 ping.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
On R1 G0/0, change subnet mask to 255.255.255.252; on R2, add ip route 0.0.0.0 0.0.0.0 10.0.0.1; for IPv6, on R2 G0/1 change address to 2001:db8:1::2/64.
Why this is correct
Ly fixes the subnet mask mismatch on R1 G0/0 (from /24 to /30), adds a default route on R2 to reach remote networks, and corrects the IPv6 subnet on R2 G0/1 to match R1's subnet (2001:db8:1::/64).
- ✗
On R1 G0/0, change subnet mask to 255.255.255.0; on R2, add ip route 0.0.0.0 0.0.0.0 10.0.0.1; for IPv6, on R2 G0/1 change address to 2001:db8:1::2/64.
Why it's wrong here
This is incorrect because changing R1's mask to /24 does not fix the mismatch; R2 uses /30, so R1 would still not see R2's IP as on-link.
- ✗
On R1 G0/0, change subnet mask to 255.255.255.252; on R2, add ip route 0.0.0.0 0.0.0.0 10.0.0.2; for IPv6, on R2 G0/1 change address to 2001:db8:2::2/64.
Why it's wrong here
This is incorrect because the default route on R2 should point to R1's G0/0 IP (10.0.0.1), not 10.0.0.2, and the IPv6 address on R2 G0/1 remains on a different subnet (2001:db8:2::/64) than R1's G0/1 (2001:db8:1::/64).
- ✗
On R1 G0/0, change subnet mask to 255.255.255.252; on R2, add ip route 0.0.0.0 0.0.0.0 10.0.0.1; for IPv6, on R2 G0/1 change address to 2001:db8:1::2/64 and on R1 G0/1 use static IPv6 instead of EUI-64.
Why it's wrong here
This is incorrect because the question specifically requires using EUI-64 on R1 G0/1; changing to static violates the requirement.
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.
✓On R1 G0/0, change subnet mask to 255.255.255.252; on R2, add ip route 0.0.0.0 0.0.0.0 10.0.0.1; for IPv6, on R2 G0/1 change address to 2001:db8:1::2/64.Correct answer▾
Why this is correct
Ly fixes the subnet mask mismatch on R1 G0/0 (from /24 to /30), adds a default route on R2 to reach remote networks, and corrects the IPv6 subnet on R2 G0/1 to match R1's subnet (2001:db8:1::/64).
✗On R1 G0/0, change subnet mask to 255.255.255.0; on R2, add ip route 0.0.0.0 0.0.0.0 10.0.0.1; for IPv6, on R2 G0/1 change address to 2001:db8:1::2/64.Wrong answer — click to see why▾
Why this is wrong here
The subnet mask on R1 G0/0 should be /30 to match R2, not /24.
Why candidates choose this
Candidates might think keeping the /24 mask is fine because it is a larger subnet, but the mismatch prevents direct communication.
✗On R1 G0/0, change subnet mask to 255.255.255.252; on R2, add ip route 0.0.0.0 0.0.0.0 10.0.0.2; for IPv6, on R2 G0/1 change address to 2001:db8:2::2/64.Wrong answer — click to see why▾
Why this is wrong here
The default gateway must be the neighbor's IP address, and IPv6 subnets must match for direct communication.
Why candidates choose this
Candidates may confuse the next-hop IP or think IPv6 subnets can be different as long as they are unique.
✗On R1 G0/0, change subnet mask to 255.255.255.252; on R2, add ip route 0.0.0.0 0.0.0.0 10.0.0.1; for IPv6, on R2 G0/1 change address to 2001:db8:1::2/64 and on R1 G0/1 use static IPv6 instead of EUI-64.Wrong answer — click to see why▾
Why this is wrong here
The requirement states EUI-64 on R1 G0/1, so static is not allowed.
Why candidates choose this
Candidates might think static is simpler and still works, but the question explicitly mandates EUI-64.
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
Default route
A default route is a catch-all routing entry that tells a network device where to send packets when no specific route matches the destination address.
Key term
Ping
Ping is a network utility used to test whether a remote computer or device is reachable across an IP network and to measure the round-trip time of data packets.
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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.