3.7. WLAN Physical Infrastructure

💡 First Principle: Wireless infrastructure connects to the wired network just like any other device—APs need power (PoE), data (Ethernet), and proper VLAN assignment. But unlike a regular PC, an AP's wired configuration directly affects wireless performance. Get the wired side wrong, and your wireless users suffer.

What happens when AP infrastructure fails: Consider this scenario—an AP connects to a switch port in the wrong VLAN. The AP can't reach the WLC, so it doesn't boot properly. Wireless users in that area get nothing. Or worse: the AP boots but user traffic gets tagged to the wrong VLAN. Sales team laptops suddenly appear on the HR network. Wired mistakes create wireless nightmares.

Consider this troubleshooting situation: Users complain that a specific AP keeps rebooting. You check the switchport and find it's not PoE-enabled, or the PoE budget is exhausted. The AP starts up, draws power, the switch can't deliver, the AP reboots. Understanding the physical requirements (power, data, management VLAN) lets you troubleshoot what looks like a "wireless" problem.

AP Connections:

• Ethernet: Access port (for autonomous) or trunk (for WLC-managed with local switching)
• Power: PoE from switch or power injector
• Management: Through WLC (lightweight) or direct (autonomous)

WLC Connections:

• Service port: Out-of-band management (different subnet)
• Distribution port(s): Trunk connections to switches
• LAG: Multiple ports bonded for bandwidth/redundancy

AP Port (Access port to WLC):

Switch(config)# interface GigabitEthernet0/1
Switch(config-if)# switchport mode access
Switch(config-if)# switchport access vlan 100    ! AP management VLAN
Switch(config-if)# spanning-tree portfast
Switch(config-if)# spanning-tree bpduguard enable

WLC Port (Trunk for multiple WLANs):

Switch(config)# interface GigabitEthernet0/24
Switch(config-if)# switchport mode trunk
Switch(config-if)# switchport trunk allowed vlan 100,110,120