Hi Roberto,
Hopefully the attached docs will answer your question:
Cisco Aironet 1100 Series
Using VLANs with Cisco Aironet Wireless Equipment
Deprecated versions of Cisco Aironet software permit binding multiple SSIDs to one VLAN. Current versions do not.
http://www.cisco.com/en/US/products/hw/wireless/ps4570/products_configuration_example09186a00801d0815.shtml#
Cisco IOS Software Configuration Guide for Cisco Aironet Access Points, 12.2(15)JA
Configuring Multiple SSIDs
vlan vlan-id
(Optional) Assign the SSID to a VLAN on your network. Client devices that associate using the SSID are grouped into this VLAN. You can assign only one SSID to a VLAN.
http://www.cisco.com/en/US/products/hw/wireless/ps4570/products_configuration_guide_chapter09186a00802085c4.html
Hope this helps!
Rob
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