Wired Access Switching and VLANs
What this domain covers
This domain tests how access switches deliver user and AP connectivity. Understand VLANs and their benefits (segmentation, security, broadcast control), access ports (one untagged VLAN, typically to endpoints) versus trunk ports (carry multiple VLANs, 802.1Q tagged, typically switch-to-switch or switch-to-AP). Know the native VLAN concept on trunks and that mismatched native VLANs cause problems. Understand Spanning Tree Protocol (STP) purpose - preventing Layer 2 loops - and rapid variants (RSTP) that converge faster. Know link aggregation (LACP) for bandwidth and redundancy, and Power over Ethernet (PoE) for APs and phones, including PoE standards and power budgeting.
Traps to watch
A classic trap: an AP connected to a switch port that is configured as an access port instead of a trunk will not pass multiple SSID VLANs. Another: forgetting that a trunk needs matching allowed-VLAN lists on both ends. STP questions often test root bridge election (lowest bridge ID wins) and why you should not disable STP to "fix" a loop. PoE questions test that a port must have PoE enabled and enough power budget.
Worked example / rule of thumb
Rule of thumb: endpoints get access ports; infrastructure (switches, APs with multiple VLANs) gets trunk ports. Example: an AP serving employee and guest SSIDs needs a trunk carrying both VLANs, plus PoE. If only one SSID/VLAN is needed, an access port can work - but design for the trunk.