CCNA Network Infrastructure and Connectivity Practice Question
Network Topology
You are connected to R1. Configure IPv4 and IPv6 addressing on R1's GigabitEthernet0/0 and GigabitEthernet0/1 interfaces so that R1 can ping both R2's IPv4 address (203.0.113.2) and R2's IPv6 address (2001:db8:1::2). The current configuration has an incorrect subnet mask on G0/0, missing default gateway, and R1's G0/1 has a duplicate IPv4 address with R3. Also, use EUI-64 for IPv6 on G0/0 and static IPv6 assignment on G0/1. Ensure all issues are resolved and connectivity verified.
⚠ Common exam trap
Watch out for subnet mask mismatches (e.g., /24 vs /30) and duplicate IP addresses. Also, note the specific IPv6 addressing requirements: EUI-64 on one interface and static on the other. Don't assume a default gateway can be any IP in the subnet; it must be the neighbor's IP.
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 subnet mask to 255.255.255.252, add default gateway 203.0.113.2, change G0/1 IPv4 to 192.168.1.254, enable IPv6 routing, configure G0/0 with ipv6 address 2001:db8:1::/64 eui-64, and G0/1 with ipv6 address 2001:db8:2::1/64.
The subnet mask on G0/0 was incorrectly set to /24 instead of /30. While a /24 mask on 203.0.113.1 would include 203.0.113.2 in the same subnet from R1's perspective, the mismatch with R2's /30 mask leads to inconsistent subnet definitions and potential ARP or routing issues. Additionally, no default gateway was configured, so traffic to remote networks would fail. On G0/1, the IPv4 address 192.168.1.1 was already used by R3, causing a duplicate IP conflict. IPv6 was not configured on either interface. The fix involved correcting the subnet mask on G0/0 to 255.255.255.252, adding a default gateway (203.0.113.2), assigning a unique IPv4 address to G0/1 (192.168.1.254), enabling IPv6 routing globally with `ipv6 unicast-routing`, configuring EUI-64 on G0/0 (`ipv6 address 2001:db8:1::/64 eui-64`), and static IPv6 on G0/1 (`ipv6 address 2001:db8:2::1/64`).
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 subnet mask to 255.255.255.252, add default gateway 203.0.113.2, change G0/1 IPv4 to 192.168.1.254, enable IPv6 routing, configure G0/0 with ipv6 address 2001:db8:1::/64 eui-64, and G0/1 with ipv6 address 2001:db8:2::1/64.
Why this is correct
Ly resolves all issues: the /30 mask matches R2's subnet, the default gateway points to R2, the duplicate IP is avoided by using .254, IPv6 routing is enabled, EUI-64 is used on G0/0, and static IPv6 is assigned on G0/1.
- ✗
Change G0/0 subnet mask to 255.255.255.0, add default gateway 203.0.113.1, change G0/1 IPv4 to 192.168.1.254, enable IPv6 routing, configure G0/0 with ipv6 address 2001:db8:1::1/64, and G0/1 with ipv6 address 2001:db8:2::1/64.
Why it's wrong here
This is incorrect because the subnet mask on G0/0 remains /24, which does not match R2's /30 subnet, and the default gateway 203.0.113.1 is not R2's IP. Additionally, IPv6 on G0/0 is statically assigned instead of using EUI-64.
- ✗
Change G0/0 subnet mask to 255.255.255.252, add default gateway 203.0.113.2, change G0/1 IPv4 to 192.168.1.1, enable IPv6 routing, configure G0/0 with ipv6 address 2001:db8:1::/64 eui-64, and G0/1 with ipv6 address 2001:db8:2::1/64.
Why it's wrong here
This option is incorrect because assigning 192.168.1.1 to G0/1 duplicates R3's interface IPv4 address, creating a duplicate address conflict that will cause unreliable routing and possible interface shutdown. While the /30 mask, default gateway 203.0.113.2, and IPv6 configuration (EUI-64 on G0/0, static on G0/1) are all correct, the IPv4 addressing error on G0/1 invalidates the entire configuration. Two devices on the same broadcast domain must have unique IPv4 addresses; otherwise, address conflict detection triggers and prevents normal operation.
- ✗
Change G0/0 subnet mask to 255.255.255.252, add default gateway 203.0.113.2, change G0/1 IPv4 to 192.168.1.254, enable IPv6 routing, configure G0/0 with ipv6 address 2001:db8:1::1/64, and G0/1 with ipv6 address 2001:db8:2::/64 eui-64.
Why it's wrong here
This option fails because it reverses the required IPv6 assignment methods: G0/0 is given a static address (2001:db8:1::1/64) when EUI-64 is required, and G0/1 is given an EUI-64 address when a static address is required. EUI-64 automatically derives the interface identifier from the MAC address, so using a static address on G0/0 does not satisfy the stated requirement, and using EUI-64 on G0/1 produces an unpredictable address that does not match the expected static address 2001:db8:2::1/64. The IPv4 settings are correct, but the IPv6 scheme is swapped, making the configuration noncompliant with the topology's addressing plan.
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 subnet mask to 255.255.255.252, add default gateway 203.0.113.2, change G0/1 IPv4 to 192.168.1.254, enable IPv6 routing, configure G0/0 with ipv6 address 2001:db8:1::/64 eui-64, and G0/1 with ipv6 address 2001:db8:2::1/64.Correct answer▾
Why this is correct
Ly resolves all issues: the /30 mask matches R2's subnet, the default gateway points to R2, the duplicate IP is avoided by using .254, IPv6 routing is enabled, EUI-64 is used on G0/0, and static IPv6 is assigned on G0/1.
✗Change G0/0 subnet mask to 255.255.255.0, add default gateway 203.0.113.1, change G0/1 IPv4 to 192.168.1.254, enable IPv6 routing, configure G0/0 with ipv6 address 2001:db8:1::1/64, and G0/1 with ipv6 address 2001:db8:2::1/64.Wrong answer — click to see why▾
Why this is wrong here
The subnet mask /24 is too large, causing a mismatch with R2's /30; the default gateway must be R2's IP (203.0.113.2); EUI-64 is not used on G0/0.
Why candidates choose this
Candidates might think a /24 mask is standard for Ethernet and that the default gateway could be any IP in the subnet, or they may overlook the EUI-64 requirement.
✗Change G0/0 subnet mask to 255.255.255.252, add default gateway 203.0.113.2, change G0/1 IPv4 to 192.168.1.1, enable IPv6 routing, configure G0/0 with ipv6 address 2001:db8:1::/64 eui-64, and G0/1 with ipv6 address 2001:db8:2::1/64.Wrong answer — click to see why▾
Why this is wrong here
The duplicate IPv4 address on G0/1 is not resolved; it still uses 192.168.1.1 which is already assigned to R3.
Why candidates choose this
Candidates might forget that the duplicate IP issue must be fixed by using a different address, or they may assume the conflict is automatically resolved.
✗Change G0/0 subnet mask to 255.255.255.252, add default gateway 203.0.113.2, change G0/1 IPv4 to 192.168.1.254, enable IPv6 routing, configure G0/0 with ipv6 address 2001:db8:1::1/64, and G0/1 with ipv6 address 2001:db8:2::/64 eui-64.Wrong answer — click to see why▾
Why this is wrong here
EUI-64 is required on G0/0, not G0/1; static IPv6 is required on G0/1, not G0/0.
Why candidates choose this
Candidates might confuse which interface uses EUI-64 versus static assignment, or think EUI-64 can be used on any interface regardless of requirements.
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
Subnet
A subnet is a logical subdivision of an IP network, created by partitioning a larger network address space using subnet masks.
Key term
IPv4 address
An IPv4 address is a unique 32-bit numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
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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.