iwpriv

http://madwifi-project.org/wiki/UserDocs/iwpriv

Locking to a Specific Mode
To lock the card to a specific mode, use:

iwpriv ath0 mode 11a To lock to 11a only.
iwpriv ath0 mode 11b To lock to 11b only.
iwpriv ath0 mode 11g To lock to 11g only.
iwpriv ath0 mode 0 (default) autoselect mode.


Changing Authentication Mode.

Use:
iwpriv ath0 authmode 1 To use open authentication.
iwpriv ath0 authmode 2 To use shared key authentication.
iwpriv ath0 authmode 3 To use 802.1x authentication.