CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 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.
R1#show running-config | section interface
interface GigabitEthernet0/0
ip address 198.51.100.1 255.255.255.252
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
GigabitEthernet0/0 198.51.100.1 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#show ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 198.51.100.2 0 aabb.cc00.0200 ARPA GigabitEthernet0/0
Internet 192.168.1.1 - aabb.cc00.0100 ARPA GigabitEthernet0/1
Internet 192.168.1.10 0 aabb.cc00.0300 ARPA GigabitEthernet0/1
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.
This option correctly fixes the subnet mask on G0/0 to match the /24 network, adds a global unicast IPv6 address and enables IPv6 on both interfaces, and resolves the IP conflict on G0/1 by using an unused address (192.168.1.254) that is typically the default gateway for VLAN 10.
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.
Why wrong: This is incorrect because the subnet mask on G0/0 remains /30 (255.255.255.252), which does not match the /24 network of R2, so R1 will still consider R2 unreachable. Additionally, the IP address 192.168.1.1 on G0/1 is already in use, causing a conflict.
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.
Why wrong: This is incorrect because IPv6 is not configured on G0/1, so R1 cannot reach IPv6 hosts on VLAN 10. The question requires both IPv4 and IPv6 addressing on both interfaces.
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 wrong: This is incorrect because the subnet mask on G0/0 remains /30, which does not match the /24 network of R2. R1 will not be able to reach R2 because the subnet mask mismatch causes R1 to consider R2's IP as not directly connected.
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 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.
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.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 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.
Why this is correct
This option correctly fixes the subnet mask on G0/0 to match the /24 network, adds a global unicast IPv6 address and enables IPv6 on both interfaces, and resolves the IP conflict on G0/1 by using an unused address (192.168.1.254) that is typically the default gateway for VLAN 10.
Related concept
Access ports place end devices into a single VLAN.
✗
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.
Why it's wrong here
This is incorrect because the subnet mask on G0/0 remains /30 (255.255.255.252), which does not match the /24 network of R2, so R1 will still consider R2 unreachable. Additionally, the IP address 192.168.1.1 on G0/1 is already in use, causing a conflict.
✗
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.
Why it's wrong here
This is incorrect because IPv6 is not configured on G0/1, so R1 cannot reach IPv6 hosts on VLAN 10. The question requires both IPv4 and IPv6 addressing on both interfaces.
✗
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 it's wrong here
This is incorrect because the subnet mask on G0/0 remains /30, which does not match the /24 network of R2. R1 will not be able to reach R2 because the subnet mask mismatch causes R1 to consider R2's IP as not directly connected.
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 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.Correct answer▾
Why this is correct
This option correctly fixes the subnet mask on G0/0 to match the /24 network, adds a global unicast IPv6 address and enables IPv6 on both interfaces, and resolves the IP conflict on G0/1 by using an unused address (192.168.1.254) that is typically the default gateway for VLAN 10.
✗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.Wrong answer — click to see why▾
Why this is wrong here
The subnet mask on G0/0 must be /24 to match the connected network; a /30 mask would put R2 in a different subnet. Also, the duplicate IP on G0/1 is not resolved.
Why candidates choose this
Candidates might think the original /30 mask is correct for a point-to-point link, but the question states R2 is on 198.51.100.0/24, so the mask must match.
✗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.Wrong answer — click to see why▾
Why this is wrong here
IPv6 must be configured on both interfaces to enable IPv6 connectivity. Omitting IPv6 on G0/1 leaves the interface without IPv6 capability.
Why candidates choose this
Candidates might focus only on IPv4 issues and forget that IPv6 configuration is explicitly required in the question.
✗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.Wrong answer — click to see why▾
Why this is wrong here
The subnet mask on G0/0 must be changed to /24 to match the network 198.51.100.0/24. Keeping /30 is the original wrong configuration.
Why candidates choose this
Candidates might think that enabling IPv6 and fixing the IP conflict is sufficient, but the subnet mask error on G0/0 must also be corrected.
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: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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 VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: 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. — 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.
What should I do if I get this 200-301 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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