An administrator configures two separate VLANs—VLAN (Sales) and VLAN (Marketing)—on a single Layer 2 switch. Host computers in both departments are connected to switch access ports assigned to their respective VLAN IDs. Although physical links are up and all devices are correctly assigned IP addresses within their subnets, hosts in VLAN cannot communicate with hosts in VLAN . Which of the following best explains why these hosts cannot communicate, and what is required to enable connectivity between them?
- VLANs create separate Layer 2 broadcast domains; therefore, a Layer 3 routing device, such as a router or multi-layer switch, is required to forward traffic between them.Answer
- BAccess ports block inter-subnet traffic by default; converting all host access ports into 802.1Q trunk ports will allow untagged communication between VLAN and VLAN .
- CThe switch drops inter-VLAN frames because the native VLAN on the switch has not been set to VLAN to match the Sales department subnet.
- DSpanning Tree Protocol (STP) has placed the switch ports into a blocking state due to a mismatch, requiring an adjustment to the STP root bridge priority.
Answer
VLANs create separate Layer 2 broadcast domains; therefore, a Layer 3 routing device, such as a router or multi-layer switch, is required to forward traffic between them.
Each VLAN configured on a switch acts as a separate Layer 2 broadcast domain. Because Layer 2 switches forward Ethernet frames strictly within the origin VLAN, traffic destined for another VLAN must be forwarded to a Layer 3 device (such as a router or Layer 3 switch) capable of routing packets between IP subnets.
Step-by-Step Solution
Key Concept
VLAN Isolation and Inter-VLAN Routing Requirements