Return-path: Received: from mail-bk0-f46.google.com ([209.85.214.46]:64168 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752633Ab2BTJsH (ORCPT ); Mon, 20 Feb 2012 04:48:07 -0500 Received: by bkcjm19 with SMTP id jm19so4382963bkc.19 for ; Mon, 20 Feb 2012 01:48:06 -0800 (PST) From: Christian Lamparter To: Yingang Fu Subject: Re: AP send null-data packet? Date: Mon, 20 Feb 2012 10:48:01 +0100 Cc: linux-wireless@vger.kernel.org References: In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Message-Id: <201202201048.01883.chunkeey@googlemail.com> (sfid-20120220_104814_747407_4D8B618A) Sender: linux-wireless-owner@vger.kernel.org List-ID: On Monday, February 20, 2012 08:12:34 AM Yingang Fu wrote: > It is wired that my AP send the station a null-date packet. > As i know that this packet could only been sent by the station. > Under which case the AP will send out this type of packet? Don't know much about other AP software. But hostapd sends them to check if a station is still in range and active. quote from hostapd.conf: # Station inactivity limit # # If a station does not send anything in ap_max_inactivity seconds, an # empty data frame is sent to it in order to verify whether it is # still in range. If this frame is not ACKed, the station will be # disassociated and then deauthenticated. This feature is used to # clear station table of old entries when the STAs move out of the # range. Regards, Chr