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.
Network Topology
You are troubleshooting a client connectivity issue on PC1, which is connected to switch SW1. PC1 reports that it cannot access the internet, but it can ping its default gateway (192.168.1.1). The network uses VLAN 10 for the client subnet. Examine the following show outputs: On PC1, ipconfig shows IP 192.168.1.10, default gateway 192.168.1.1, DNS server 192.168.1.1. On SW1, show running-config includes 'interface Vlan10' with IP 192.168.1.1 255.255.255.0, but no 'ip dns server' and no 'ip name-server' commands. SW1's show ip route displays a default route via 203.0.113.1. Identify the root cause. Configure the necessary fix on the appropriate device to restore full connectivity.
PC1 ipconfig output:
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . : example.local
IPv4 Address. . . . . . . . . . . : 192.168.1.100
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.1.1
Ping results from PC1:
C:\>ping 192.168.1.1
Reply from 192.168.1.1: bytes=32 time<1ms TTL=128
C:\>ping 8.8.8.8
Reply from 192.168.1.1: Destination host unreachable.
C:\>ping www.courseiva.com
Ping request could not find host www.courseiva.com. Please check the name and try again.
SW1 running-config (partial):
hostname SW1
!
vlan 10
name CLIENT_VLAN
!
interface Vlan10
ip address 192.168.1.1 255.255.255.0
no shutdown
!
ip route 0.0.0.0 0.0.0.0 203.0.113.1
!
interface GigabitEthernet0/1
switchport mode access
switchport access vlan 10
spanning-tree portfast
!
interface GigabitEthernet0/2
no switchport
ip address 203.0.113.2 255.255.255.252
!
A
Configure 'ip dns server' and 'ip name-server 8.8.8.8' on SW1.
This enables the DNS forwarding service on the switch and specifies an upstream DNS server, allowing PC1 to resolve internet hostnames via the switch.
B
Configure 'ip default-gateway 192.168.1.1' on SW1.
Why wrong: This is incorrect because the switch already has an SVI for VLAN 10 and a default route to the internet. The 'ip default-gateway' command is used for switch management access when IP routing is disabled, but here routing is enabled and the issue is DNS, not gateway reachability.
C
Configure 'ip route 0.0.0.0 0.0.0.0 203.0.113.1' on SW1.
Why wrong: This is incorrect because the switch already has a default route to 203.0.113.1 (as stated in the scenario). Adding another default route is redundant and does not address the DNS issue.
D
Configure 'ip domain-lookup' on SW1.
Why wrong: This is incorrect because 'ip domain-lookup' enables DNS resolution on the switch itself, but it does not configure a DNS server. Without a DNS server, the switch cannot resolve names, and clients using the switch as DNS will still fail.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure 'ip dns server' and 'ip name-server 8.8.8.8' on SW1.
PC1 is configured with DNS server 192.168.1.1, which is the switch SW1. However, SW1 lacks DNS forwarding capability. To enable DNS relay on the switch, both the 'ip dns server' command (to activate the DNS forwarder) and 'ip name-server 8.8.8.8' (to point to an upstream resolver) are required. Option A provides the necessary configuration to restore DNS resolution and internet connectivity.
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.
✓
Configure 'ip dns server' and 'ip name-server 8.8.8.8' on SW1.
Why this is correct
This enables the DNS forwarding service on the switch and specifies an upstream DNS server, allowing PC1 to resolve internet hostnames via the switch.
Related concept
Access ports place end devices into a single VLAN.
✗
Configure 'ip default-gateway 192.168.1.1' on SW1.
Why it's wrong here
This is incorrect because the switch already has an SVI for VLAN 10 and a default route to the internet. The 'ip default-gateway' command is used for switch management access when IP routing is disabled, but here routing is enabled and the issue is DNS, not gateway reachability.
✗
Configure 'ip route 0.0.0.0 0.0.0.0 203.0.113.1' on SW1.
Why it's wrong here
This is incorrect because the switch already has a default route to 203.0.113.1 (as stated in the scenario). Adding another default route is redundant and does not address the DNS issue.
✗
Configure 'ip domain-lookup' on SW1.
Why it's wrong here
This is incorrect because 'ip domain-lookup' enables DNS resolution on the switch itself, but it does not configure a DNS server. Without a DNS server, the switch cannot resolve names, and clients using the switch as DNS will still fail.
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.
✓Configure 'ip dns server' and 'ip name-server 8.8.8.8' on SW1.Correct answer▾
Why this is correct
This enables the DNS forwarding service on the switch and specifies an upstream DNS server, allowing PC1 to resolve internet hostnames via the switch.
✗Configure 'ip default-gateway 192.168.1.1' on SW1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that 'ip default-gateway' is for management access on a Layer 2 switch, not for client connectivity. The switch already has a default route (203.0.113.1) for routing traffic.
Why candidates choose this
Candidates might confuse 'ip default-gateway' with a default route or think that the gateway is missing because PC1 cannot reach the internet, but PC1 can ping the gateway, so the gateway is reachable.
✗Configure 'ip route 0.0.0.0 0.0.0.0 203.0.113.1' on SW1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the default route already exists; the problem is not routing but DNS resolution. The switch can route traffic but cannot resolve names for clients.
Why candidates choose this
Candidates often assume that internet connectivity issues are always due to missing default routes, especially when the client can ping the gateway but not the internet. However, PC1 can ping the gateway, so routing is likely fine.
✗Configure 'ip domain-lookup' on SW1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that 'ip domain-lookup' is enabled by default and does not specify a DNS server. The missing piece is the 'ip name-server' command to provide the DNS server address.
Why candidates choose this
Candidates might think that enabling DNS lookup is sufficient, but without a server address, the switch cannot forward queries. This command alone does not fix client DNS resolution.
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.
Trap categories for this question
Command / output trap
This is incorrect because the switch already has an SVI for VLAN 10 and a default route to the internet. The 'ip default-gateway' command is used for switch management access when IP routing is disabled, but here routing is enabled and the issue is DNS, not gateway reachability.
Scenario analysis trap
This is incorrect because the switch already has a default route to 203.0.113.1 (as stated in the scenario). Adding another default route is redundant and does not address the DNS issue.
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: Configure 'ip dns server' and 'ip name-server 8.8.8.8' on SW1. — PC1 is configured with DNS server 192.168.1.1, which is the switch SW1. However, SW1 lacks DNS forwarding capability. To enable DNS relay on the switch, both the 'ip dns server' command (to activate the DNS forwarder) and 'ip name-server 8.8.8.8' (to point to an upstream resolver) are required. Option A provides the necessary configuration to restore DNS resolution and internet connectivity.
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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