how to prove traffic is under wpa key using sniffer?

[hong zhang]

List,
   
  I setup wpa key and ping only works under auto authentication mode.
  I look at sniffer but cannot figure out it is real wpa traffic.
   
  ZCan anyone do me favor and tell me which part of packet indicates this apcket is under wpa security?
   
  Thanks.
   
   
  ----henry
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