CCNA Switching and Network Access Practice Question
Hosts in VLAN 10 need to communicate with hosts in VLAN 20. What is required for that communication to work?
⚠ Common exam trap
Do not confuse trunk links or access ports with routing functions; they serve different purposes in VLAN configurations.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A Layer 3 routing function
Traffic between VLANs must be routed. A router or multilayer switch provides the Layer 3 function needed for inter-VLAN communication.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A DHCP server
Why it's wrong here
A DHCP server only supplies IP configuration (address, subnet mask, gateway, DNS) via DHCP messages. Even if every host in VLAN 10 and VLAN 20 receives a valid address from the server, the DHCP protocol itself does not inspect or forward packets between subnets; it has no forwarding table. Inter-VLAN traffic still requires a Layer 3 device to route from the source subnet to the destination subnet, so DHCP is not a substitute for routing.
When this WOULD be correct
If the question asked about enabling IP address assignment for hosts in VLAN 10 and VLAN 20, where both VLANs are on the same network segment, then a DHCP server would be necessary to ensure that devices in both VLANs receive valid IP addresses.
- ✗
A DNS server
Why it's wrong here
A DNS server converts human-readable names into IP addresses using the application-layer DNS protocol. This name resolution process does not affect or enable the forwarding path between VLANs; once a host learns the destination IP from DNS, the packet still needs a router to traverse the Layer 3 boundary. In fact, without inter-VLAN routing, DNS queries themselves would fail if the DNS server resides in a different VLAN, because the query frames would never leave the local segment.
When this WOULD be correct
In a question asking about network services needed for host name resolution in a multi-VLAN environment, where hosts in different VLANs need to resolve each other's domain names, a DNS server would be essential for that purpose.
- ✓
A Layer 3 routing function
Why this is correct
Layer 3 routing is the required mechanism because VLANs represent separate broadcast domains and distinct IP subnets. A router or multilayer switch must inspect the destination IP address, perform a route lookup, and rewrite the frame's MAC addresses before forwarding the packet to the destination VLAN. Without this IP-level forwarding decision, frames remain confined to their originating Layer 2 domain, so no traffic can cross the VLAN boundary.
- ✗
A second access switch
Why it's wrong here
Adding a second access switch simply expands the Layer 2 topology by providing more ports and possibly extending a VLAN across more switches. Because an access switch operates at Layer 2, it uses MAC address tables to forward frames within the same broadcast domain and cannot make IP-based routing decisions. Regardless of how many access switches exist, VLAN 10 and VLAN 20 remain isolated at Layer 2, so a Layer 3 routing function is still mandatory.
When this WOULD be correct
If the exam question specified that the network was experiencing performance issues due to too many VLANs being managed by a single switch, and suggested that adding a second access switch could help distribute the load and improve communication efficiency, then this option would be correct.
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.
✓A Layer 3 routing functionCorrect answer▾
Why this is correct
Layer 3 routing is the required mechanism because VLANs represent separate broadcast domains and distinct IP subnets. A router or multilayer switch must inspect the destination IP address, perform a route lookup, and rewrite the frame's MAC addresses before forwarding the packet to the destination VLAN. Without this IP-level forwarding decision, frames remain confined to their originating Layer 2 domain, so no traffic can cross the VLAN boundary.
✗A DHCP serverWrong answer — click to see why▾
Why this is wrong here
A DHCP server is not required for communication between VLANs; it only assigns IP addresses to devices within a network. VLAN communication requires routing, which a DHCP server does not provide.
★ When this WOULD be the correct answer
If the question asked about enabling IP address assignment for hosts in VLAN 10 and VLAN 20, where both VLANs are on the same network segment, then a DHCP server would be necessary to ensure that devices in both VLANs receive valid IP addresses.
Why candidates choose this
Candidates may confuse the need for IP address assignment with the requirement for inter-VLAN communication, leading them to believe that a DHCP server is essential for connectivity between VLANs.
✗A DNS serverWrong answer — click to see why▾
Why this is wrong here
A DNS server is not required for VLAN communication, as DNS resolves domain names to IP addresses, which does not facilitate inter-VLAN routing. Communication between VLANs requires Layer 3 routing, not name resolution.
★ When this WOULD be the correct answer
In a question asking about network services needed for host name resolution in a multi-VLAN environment, where hosts in different VLANs need to resolve each other's domain names, a DNS server would be essential for that purpose.
Why candidates choose this
Candidates may confuse the need for network services in a multi-VLAN setup, mistakenly believing that DNS is necessary for communication, as it is often associated with network functionality and connectivity.
✗A second access switchWrong answer — click to see why▾
Why this is wrong here
A second access switch is not required for VLAN communication; VLANs can communicate through a Layer 3 device such as a router or a Layer 3 switch. The existing switch infrastructure can handle VLANs without needing additional switches.
★ When this WOULD be the correct answer
If the exam question specified that the network was experiencing performance issues due to too many VLANs being managed by a single switch, and suggested that adding a second access switch could help distribute the load and improve communication efficiency, then this option would be correct.
Why candidates choose this
Candidates might choose this option because they associate VLANs with physical switch configurations and believe that additional hardware is necessary for inter-VLAN communication, overlooking the role of Layer 3 routing.
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?”
Visual reference
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
Key term
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.