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.
Exhibit
R1# show running-config
Building configuration...
Current configuration : 1250 bytes
!
hostname R1
!
interface GigabitEthernet0/0
ip address 192.0.2.1 255.255.255.252
no shutdown
!
interface GigabitEthernet0/1
ipv6 address 2001:db8:1::1/64
no shutdown
!
ip route 0.0.0.0 0.0.0.0 192.0.2.2
!
end
R1# show ip interface brief
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 192.0.2.1 YES manual up up
GigabitEthernet0/1 unassigned YES manual up up
R1# show ipv6 interface brief
GigabitEthernet0/0 [unassigned]
GigabitEthernet0/1 [2001:db8:1::1]
You are connected to R1. The network has three routers: R1, R2, and R3. R1's G0/0 is connected to R2's G0/0, and R1's G0/1 is connected to R3's G0/1. The goal is to configure R1 so that it can ping both R2 (192.0.2.2/30) and R3 (2001:db8:1::2/64). Currently, R1 cannot ping R2 due to a wrong subnet mask on R1's G0/0, and R3 is using an IPv6 EUI-64 address but R1 has been given a static IPv6 address that conflicts. Fix both issues and verify connectivity.
R1# show running-config
Building configuration...
Current configuration : 1250 bytes
!
hostname R1
!
interface GigabitEthernet0/0
ip address 192.0.2.1 255.255.255.252
no shutdown
!
interface GigabitEthernet0/1
ipv6 address 2001:db8:1::1/64
no shutdown
!
ip route 0.0.0.0 0.0.0.0 192.0.2.2
!
end
R1# show ip interface brief
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 192.0.2.1 YES manual up up
GigabitEthernet0/1 unassigned YES manual up up
R1# show ipv6 interface brief
GigabitEthernet0/0 [unassigned]
GigabitEthernet0/1 [2001:db8:1::1]
A
On G0/0, change the subnet mask to 255.255.255.252; on G0/1, remove the static IPv6 address and configure an EUI-64 address.
This is correct because R1's G0/0 mask must be /30 (255.255.255.252) to match R2's subnet, and using EUI-64 on G0/1 ensures a unique IPv6 address that avoids conflict with R3's EUI-64 address.
B
On G0/0, change the IP address to 192.0.2.2/30; on G0/1, change the IPv6 address to 2001:db8:1::2/64.
Why wrong: This is incorrect because changing R1's G0/0 IP to 192.0.2.2 would duplicate R2's address, and manually setting G0/1 to 2001:db8:1::2 does not resolve the conflict if R3's EUI-64 address happens to be the same; it also does not fix the mask issue.
C
On G0/0, change the subnet mask to 255.255.255.0; on G0/1, change the IPv6 address to 2001:db8:1::1/64 with EUI-64.
Why wrong: This is incorrect because a /24 mask on G0/0 would still not match R2's /30, causing a subnet mismatch; also, configuring EUI-64 on G0/1 while keeping the static address 2001:db8:1::1 would not resolve the conflict because the static address remains.
D
On G0/0, change the IP address to 192.0.2.2/30; on G0/1, remove the static IPv6 address and configure an EUI-64 address.
Why wrong: This is incorrect because changing R1's G0/0 IP to 192.0.2.2 duplicates R2's address, causing an IP conflict; while the G0/1 fix is correct, the G0/0 change is wrong.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
On G0/0, change the subnet mask to 255.255.255.252; on G0/1, remove the static IPv6 address and configure an EUI-64 address.
The problem has two issues. First, R1's G0/0 has IP 192.0.2.1 but its subnet mask is incorrectly set to 255.255.255.0 (/24) instead of the required 255.255.255.252 (/30) that matches R2's /30. This mask mismatch causes R1 to misclassify the subnet, preventing successful ping to R2. The fix is to change the mask to 255.255.255.252. Second, R1's G0/1 is configured with a static IPv6 address 2001:db8:1::1/64, but R3 uses EUI-64 and generates its address as 2001:db8:1::2. This duplicate address risk breaks communication. The correct solution is to remove the static IPv6 address and enable EUI-64 on G0/1, allowing R1 to derive a unique address from the prefix. Options B and D incorrectly change R1's IPv4 address to 192.0.2.2, which duplicates R2's address. Option B also sets a static IPv6 address of ::2, duplicating R3's address. Option C changes the mask to /24, which would temporarily allow communication but violates the intended point-to-point /30 design and does not adopt best practices; it also incorrectly applies a static IPv6 address with EUI-64, which is unnecessary and could still conflict.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 G0/0, change the subnet mask to 255.255.255.252; on G0/1, remove the static IPv6 address and configure an EUI-64 address.
Why this is correct
This is correct because R1's G0/0 mask must be /30 (255.255.255.252) to match R2's subnet, and using EUI-64 on G0/1 ensures a unique IPv6 address that avoids conflict with R3's EUI-64 address.
On G0/0, change the IP address to 192.0.2.2/30; on G0/1, change the IPv6 address to 2001:db8:1::2/64.
Why it's wrong here
This is incorrect because changing R1's G0/0 IP to 192.0.2.2 would duplicate R2's address, and manually setting G0/1 to 2001:db8:1::2 does not resolve the conflict if R3's EUI-64 address happens to be the same; it also does not fix the mask issue.
✗
On G0/0, change the subnet mask to 255.255.255.0; on G0/1, change the IPv6 address to 2001:db8:1::1/64 with EUI-64.
Why it's wrong here
This is incorrect because a /24 mask on G0/0 would still not match R2's /30, causing a subnet mismatch; also, configuring EUI-64 on G0/1 while keeping the static address 2001:db8:1::1 would not resolve the conflict because the static address remains.
✗
On G0/0, change the IP address to 192.0.2.2/30; on G0/1, remove the static IPv6 address and configure an EUI-64 address.
Why it's wrong here
This is incorrect because changing R1's G0/0 IP to 192.0.2.2 duplicates R2's address, causing an IP conflict; while the G0/1 fix is correct, the G0/0 change is wrong.
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 G0/0, change the subnet mask to 255.255.255.252; on G0/1, remove the static IPv6 address and configure an EUI-64 address.Correct answer▾
Why this is correct
This is correct because R1's G0/0 mask must be /30 (255.255.255.252) to match R2's subnet, and using EUI-64 on G0/1 ensures a unique IPv6 address that avoids conflict with R3's EUI-64 address.
✗On G0/0, change the IP address to 192.0.2.2/30; on G0/1, change the IPv6 address to 2001:db8:1::2/64.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: 192.0.2.2 is already used by R2, causing an IP conflict; static assignment on G0/1 does not guarantee uniqueness.
Why candidates choose this
Candidates might think changing the IP to match R2's subnet or using a different static IPv6 address solves the problem, but they overlook the mask mismatch and the need for EUI-64 to avoid duplication.
✗On G0/0, change the subnet mask to 255.255.255.0; on G0/1, change the IPv6 address to 2001:db8:1::1/64 with EUI-64.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: /24 mask is too large and does not match the /30 subnet; EUI-64 cannot be applied alongside a static address—it replaces the interface ID.
Why candidates choose this
Candidates may think a larger mask (like /24) includes the neighbor's IP, but the subnet must match exactly; they may also think adding EUI-64 to a static address is possible, but it's one or the other.
✗On G0/0, change the IP address to 192.0.2.2/30; on G0/1, remove the static IPv6 address and configure an EUI-64 address.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: 192.0.2.2 is already assigned to R2, so R1 cannot use it; the correct fix is to adjust the mask, not the IP.
Why candidates choose this
Candidates might think that since R2's IP is 192.0.2.2, R1 should use that IP to be on the same subnet, but they forget that IP addresses must be unique and the mask is the actual issue.
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: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: On G0/0, change the subnet mask to 255.255.255.252; on G0/1, remove the static IPv6 address and configure an EUI-64 address. — The problem has two issues. First, R1's G0/0 has IP 192.0.2.1 but its subnet mask is incorrectly set to 255.255.255.0 (/24) instead of the required 255.255.255.252 (/30) that matches R2's /30. This mask mismatch causes R1 to misclassify the subnet, preventing successful ping to R2. The fix is to change the mask to 255.255.255.252. Second, R1's G0/1 is configured with a static IPv6 address 2001:db8:1::1/64, but R3 uses EUI-64 and generates its address as 2001:db8:1::2. This duplicate address risk breaks communication. The correct solution is to remove the static IPv6 address and enable EUI-64 on G0/1, allowing R1 to derive a unique address from the prefix. Options B and D incorrectly change R1's IPv4 address to 192.0.2.2, which duplicates R2's address. Option B also sets a static IPv6 address of ::2, duplicating R3's address. Option C changes the mask to /24, which would temporarily allow communication but violates the intended point-to-point /30 design and does not adopt best practices; it also incorrectly applies a static IPv6 address with EUI-64, which is unnecessary and could still conflict.
What should I do if I get this 200-301 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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