220-1101 Networking Practice Question
A network technician configures a managed switch with two VLANs: VLAN 10 for workstations and VLAN 20 for servers. A workstation on VLAN 10 can ping its default gateway (192.168.10.1), and a server on VLAN 20 can ping its default gateway (192.168.20.1). However, the workstation cannot ping the server's IP address (192.168.20.10). All switch ports are configured as access ports in their respective VLANs, and the default gateways are correctly assigned. Which of the following is MOST likely needed to allow this communication?
⚠ Common exam trap
CompTIA often tests the misconception that a trunk port alone enables inter-VLAN communication, but a trunk only carries multiple VLANs over a single link; a Layer 3 routing process is still required to forward packets between VLANs.
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 router configured for inter-VLAN routing
The workstation and server are on different VLANs, which are separate Layer 2 broadcast domains. Even though each device can reach its own default gateway, communication between VLANs requires a Layer 3 device to route packets between them. A router configured for inter-VLAN routing (either router-on-a-stick or a Layer 3 switch) is necessary to forward traffic from VLAN 10 to VLAN 20.
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 router configured for inter-VLAN routing
Why this is correct
Devices in different VLANs cannot communicate without a Layer 3 device that routes between them. The router must be configured to forward traffic between VLAN 10 and VLAN 20, and the switch-to-router link must be a trunk.
- ✗
A DHCP server on each VLAN
Why it's wrong here
A DHCP server on each VLAN does not solve inter-VLAN routing because DHCP only assigns IP configurations (address, subnet mask, default gateway) but does not forward traffic between separate subnets. Even if each VLAN has its own DHCP server, devices in VLAN 10 and VLAN 20 remain in distinct broadcast domains and IP subnets; without a Layer 3 device that routes between those subnets, the devices cannot exchange traffic. Moreover, a single DHCP server can serve multiple VLANs using an IP helper address (DHCP relay), so deploying separate servers is unnecessary and does not address the missing routing function.
- ✗
A higher category Ethernet cable
Why it's wrong here
Upgrading to a higher category Ethernet cable (e.g., Cat5e to Cat6 or Cat6a) affects Layer 1 characteristics such as frequency rating, signal integrity, and maximum data rate, but it cannot enable Layer 3 packet forwarding. Inter-VLAN communication requires a router (or Layer 3 switch) that examines destination IP addresses and makes routing decisions. A better cable only increases the physical link's speed/capacity; it does not alter the switch's VLAN isolation, so frames from VLAN 10 are still never forwarded to VLAN 20 without a routing entity.
- ✗
A trunk port between the switch and the router
Why it's wrong here
A trunk port between the switch and the router is a Layer 2 link that carries 802.1Q-tagged frames for multiple VLANs, but it is not sufficient for inter-VLAN routing by itself. The router must be explicitly configured with subinterfaces (using encapsulation dot1q) and IP addresses in each VLAN's subnet, along with enabling inter-VLAN routing. Without that Layer 3 configuration, the trunk port only transports VLAN-tagged traffic to the router, which will drop or ignore it because it has no route between the VLANs. The primary missing element is the router's inter-VLAN routing configuration, not just the trunk link.
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