The role of an AP’s Ethernet port is only to get the AP be able to communicate with the ip address of the Management Interface of the WLC, so that the AP can join to the WLC.
After the AP joins to the WLC, the radio interfaces of the AP come up. This allows the Beacons to be sent in the air, via the Radios of the APs.
2 # - These Beacons (Management Frames) are used by the APs advertise the SSIDs/WLANs in the air, so that the wireless clients and pick up their SSIDs/WLANs of interest via Probe Requests (Management Frames) and Probe Responses (Management Frames). - Within these frames, there is place to put the value of the BSSID. - a BSSID is the mac address of the WLAN , which gets assigned on the creation of a WLAN. This is also known as the base mac address of the WLAN Radio.
So, when say a wireless client tries to connect a WLAN, the WLAN’s corresponding BSSID is sent within the wireless 802.11 frames .
These Wireless 802.11 frames when reach the AP, get encapsulated/enclosed within the capwap header, before being forwarded to the Controller. (The reason , as to why the capwap header is used is, because the WLC and AP talk via the capwap tunnel)
These capwap frames, get encapsulated/enclosed within the Wired/Ethernet 802.3 header, before being forwarded to the wired infrastructure. (The reason , as to why the Ethernet header is used is, because the WLC is on the wired network)
When the WLC gets the 802.3 frames, all the way from the AP, across the wired infrastructure, .. the WLC decapsulates the Ethernet header, and gets the capwap header .. the WLC decapsulates the capwap header , and gets the Wireless 802.11 header. .. from the Wireless 802.11 header, the WLC gets the BSSID .. from the BSSID, the WLC is able to get the WLAN. (because WLC has mapping of WLAN and BSSID) .. from the WLAN, the WLC is able to get the VLAN-ID (because we manually configure the VLAN-ID for a WLAN in the WLC) ..from the VLAN-ID, the WLC is able to put appropriate VLAN-Tag on the frames, before forwarding them on the Wired Infrastructure, via the trunk ports of the switch (to which the WLC is connected).
When we have to pass the data of 'multiple vlans' via the radios of the APs then the port of the switch (to which the AP is connected):
- "must" be a Trunk Port, when the mode of the AP is set to be HREAP . For reference, one may like to visit http://www.cisco.com/c/en/us/support/docs/wireless/5500-series-wireless-controllers/71250-h-reap-design-deploy.html#Trunk
- "may" simply be an Access Port (as mentioned previously), when the mode of the AP is set to be LOCAL. .
This also means,
When we have to pass the data of 'single vlan' via the radios of the APs then the port of the switch (to which the AP is connected):
- "may" simply be an Access Port when the mode of the AP is set to be HREAP.