On a single access switch, PC-A sits in VLAN 10 (subnet 10.1.10.0/24) and PC-B sits in VLAN 20 (subnet 10.1.20.0/24). Both link lights are up and each PC reaches other hosts inside its own VLAN, but PC-A cannot ping PC-B. What is required to let the two PCs communicate while keeping the VLANs separate?
- AEnable an 802.1Q trunk between the two switchports so the VLAN tags carry the traffic across.
- BAdd a Layer 3 device such as a router or multilayer switch to route between the VLAN 10 and VLAN 20 subnets. Correct
- CEnable Spanning Tree Protocol for VLAN 10 and VLAN 20 to open a forwarding path between them.
- DConfigure port security on both switchports to permit each PC's MAC address.
Why A is wrong: Trunking sounds like it connects VLANs, but an 802.1Q trunk multiplexes several VLANs onto one switch-to-switch link; it does not route packets from one VLAN subnet into another.
Why B is correct: Each VLAN is a separate broadcast domain on its own IP subnet, so traffic between them must cross a Layer 3 boundary provided by a router subinterface or a multilayer switch SVI.
Why C is wrong: STP is tempting because it manages forwarding paths, but it only prevents Layer 2 loops within a broadcast domain and never routes traffic between two different VLAN subnets.
Why D is wrong: Port security is tempting when a host cannot pass traffic, but it only limits which MAC addresses a port accepts and does nothing to forward traffic between two separate VLAN subnets.