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Does the AIR-AP1231-G-A-K9 cointain internal antenna? Or i must order an external one?
This model AIR-AP1231-G-A-K9 does not come with Internal Antennas, so they must be ordered seperately :( Here is the guide that does show the compatible Antenna models;
Cisco Aironet Antennas and Accessories Reference Guide
Hope this helps!