CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
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.
R1#show running-config | section interface
interface GigabitEthernet0/0
ip address 10.0.0.1 255.255.255.0
no shutdown
!
interface GigabitEthernet0/1
ip address 192.168.1.1 255.255.255.0
ipv6 address 2001:db8:1::/64 eui-64
no shutdown
!
interface Loopback0
ip address 203.0.113.1 255.255.255.255
!
R1#show ip route
Codes: C - connected, L - local
10.0.0.0/8 is variably subnetted, 2 subnets
C 10.0.0.0/24 is directly connected, GigabitEthernet0/0
L 10.0.0.1/32 is directly connected, GigabitEthernet0/0
192.168.1.0/24 is variably subnetted, 2 subnets
C 192.168.1.0/24 is directly connected, GigabitEthernet0/1
L 192.168.1.1/32 is directly connected, GigabitEthernet0/1
203.0.113.1/32 is directly connected, Loopback0
R2#show running-config | section interface
interface GigabitEthernet0/0
ip address 10.0.0.2 255.255.255.252
no shutdown
!
interface GigabitEthernet0/1
ip address 192.168.2.1 255.255.255.0
ipv6 address 2001:db8:2::1/64
no shutdown
!
interface Loopback0
ip address 198.51.100.1 255.255.255.255
!
R2#show ip route
Codes: C - connected, L - local
10.0.0.0/30 is subnetted, 1 subnets
C 10.0.0.0/30 is directly connected, GigabitEthernet0/0
L 10.0.0.2/32 is directly connected, GigabitEthernet0/0
192.168.2.0/24 is variably subnetted, 2 subnets
C 192.168.2.0/24 is directly connected, GigabitEthernet0/1
L 192.168.2.1/32 is directly connected, GigabitEthernet0/1
198.51.100.1/32 is directly connected, Loopback0
A
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.
This option correctly 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).
B
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 wrong: 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.
C
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 wrong: 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).
D
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 wrong: This is incorrect because the question specifically requires using EUI-64 on R1 G0/1; changing to static violates the requirement.
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.
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 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
This option correctly 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
This option correctly 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?”
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 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.
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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