The correct fix involves correcting the subnet mask on G0/0 to 255.255.255.252, adding the default gateway 203.0.113.2, assigning a unique IPv4 address to G0/1, enabling IPv6 routing, and configuring EUI-64 on G0/0 with a static IPv6 address on G0/1. This is necessary because the original /24 subnet mask on G0/0 created a mismatch with R2’s /30, leading to inconsistent subnet definitions and potential ARP failures, while the missing default gateway blocked all off-subnet traffic. On G0/1, the duplicate IPv4 address with R3 caused a conflict that required a unique address like 192.168.1.254. The CCNA 200-301 v2 exam tests your ability to troubleshoot IPv4 and IPv6 interface configuration, subnet mask alignment, and default gateway logic across dual-stack environments—a common trap is forgetting that a mismatched subnet mask can break connectivity even if the IPs are in the same range. A useful memory tip: “Mask must match, gateway catches the rest, and IPv6 needs routing enabled first.”
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 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.
R1# show running-config | section interface
interface GigabitEthernet0/0
ip address 203.0.113.1 255.255.255.0
duplex auto
speed auto
!
interface GigabitEthernet0/1
ip address 192.168.1.1 255.255.255.0
duplex auto
speed auto
!
R1# show ip interface brief
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 203.0.113.1 YES manual up up
GigabitEthernet0/1 192.168.1.1 YES manual up up
R1# show ipv6 interface brief
GigabitEthernet0/0 [unassigned]
GigabitEthernet0/1 [unassigned]
R1# ping 203.0.113.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 203.0.113.2, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R1# ping 2001:db8:1::2
% Unrecognized host or address, or protocol not running
A
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.
This option correctly 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.
B
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 wrong: 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.
C
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 wrong: This is incorrect because G0/1's IPv4 address 192.168.1.1 is the same as R3's, causing a duplicate IP conflict. The duplicate IP issue is not resolved.
D
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 wrong: This is incorrect because IPv6 on G0/0 is statically assigned instead of using EUI-64, and IPv6 on G0/1 uses EUI-64 instead of static assignment. The requirements are reversed.
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`).
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.
✓
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
This option correctly 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 is incorrect because G0/1's IPv4 address 192.168.1.1 is the same as R3's, causing a duplicate IP conflict. The duplicate IP issue is not 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.
Why it's wrong here
This is incorrect because IPv6 on G0/0 is statically assigned instead of using EUI-64, and IPv6 on G0/1 uses EUI-64 instead of static assignment. The requirements are reversed.
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
This option correctly 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?”
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: 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`).
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are connected to R1. Configure IPv4 and IPv6 addressing on R1's GigabitEthernet0/0 and GigabitEthernet0/1 interfaces so that R1 can reach R2 and the internal host on VLAN 10. R1 G0/0 connects to R2 (198.51.100.0/24), and R1 G0/1 connects to a switch with VLAN 10 (192.168.1.0/24). The current configuration has a wrong subnet mask on G0/0, missing IPv6 addresses, and a duplicate IP on G0/1. Fix all issues and verify connectivity.
hard
✓ A.On G0/0, change subnet mask to 255.255.255.0, add IPv6 address 2001:db8:1::1/64 and enable ipv6 enable; on G0/1, change IP to 192.168.1.254/24 and add IPv6 address 2001:db8:2::1/64.
B.On G0/0, change subnet mask to 255.255.255.252, add IPv6 address 2001:db8:1::1/64; on G0/1, keep IP 192.168.1.1/24 and add IPv6 address 2001:db8:2::1/64.
C.On G0/0, change subnet mask to 255.255.255.0, add IPv6 address 2001:db8:1::1/64; on G0/1, change IP to 192.168.1.254/24 but do not configure IPv6.
D.On G0/0, keep subnet mask 255.255.255.252, add IPv6 address 2001:db8:1::1/64 and enable ipv6 enable; on G0/1, change IP to 192.168.1.254/24 and add IPv6 address 2001:db8:2::1/64.
Why A: The GigabitEthernet0/0 interface had a wrong subnet mask (255.255.255.252 instead of 255.255.255.0), causing R1 to think R2 (198.51.100.2) was on a different subnet, so pings failed. Additionally, IPv6 was not configured at all; we added both a static global unicast address (2001:db8:1::1/64) and configured a static link-local address (fe80::1) on G0/0. On G0/1, the IP address 192.168.1.1 was already in use by another device (seen in ARP cache with age 0), so we changed it to 192.168.1.254 (the usual default gateway for VLAN 10). Finally, we verified with show commands and pings.
Variation 2. 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.
hard
✓ A.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
B.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
C.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
D.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 A: R1 cannot reach R2 because G0/0 has a wrong subnet mask (/24 instead of /30) and no default gateway. Also, G0/1 has a duplicate IPv4 address (10.0.0.5/30 conflicts with R2's G0/1). To fix: change G0/0 mask to /30, add a default route via 10.0.0.2, assign a unique IP to G0/1 (e.g., 192.0.2.2/30), enable IPv6 on G0/0 with EUI-64 link-local, and assign a static global unicast address to G0/1 (2001:db8:2::1/64).
Variation 3. 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.
hard
✓ 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.
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.
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.
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 A: 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.
Variation 4. You are connected to R1. Configure IPv4 and IPv6 addressing on R1's interfaces and verify reachability to R2. The current configuration has a wrong subnet mask on G0/0, missing default gateway for IPv4, and R1's IPv6 address is configured using EUI-64 while R2 uses a static IPv6 address. Fix these issues so that R1 can ping both R2's IPv4 and IPv6 addresses.
hard
✓ A.Change R1 G0/0 subnet mask to /30, add a default route via 192.0.2.2, and configure a static IPv6 address 2001:db8:1::1/64 on G0/0.
B.Change R1 G0/0 subnet mask to /30, add a default route via 192.0.2.254, and keep the EUI-64 IPv6 address on G0/0.
C.Change R1 G0/0 subnet mask to /24, add a default route via 192.0.2.2, and configure a static IPv6 address 2001:db8:1::1/64 on G0/0.
D.Change R1 G0/0 subnet mask to /30, add a default route via 192.0.2.2, and keep the EUI-64 IPv6 address on G0/0.
Why A: The problem had three issues: (1) R1's G0/0 subnet mask was /24 (255.255.255.0) but R2's G0/0 was /30 (255.255.255.252), causing an IP subnet mismatch. (2) R1 lacked a default gateway for IPv4; the static route pointed to 192.0.2.254 which is not reachable. (3) R1's IPv6 EUI-64 configuration on G0/0 generates an interface ID from the MAC, but R2 expects a static address 2001:db8:1::2/64, so R1 must use a static IPv6 address on the same subnet. The fix: change R1's G0/0 mask to /30, add a default route via R2's G0/0 IP (192.0.2.2), and configure a static IPv6 address (e.g., 2001:db8:1::1/64) on R1's G0/0.
Last reviewed: Jun 6, 2026
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