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[199.106.103.254]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-87feb583422sm1324979b3a.50.2026.09.25.08.03.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Sep 2026 08:03:17 -0700 (PDT) Message-ID: <3ea7e9ab-ed3a-4e6a-9006-b6f6af51c1fd@oss.qualcomm.com> Date: Fri, 25 Sep 2026 08:03:16 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: ath11k: Question about active scanning of DFS channels To: Alexander Wilhelm , Jeff Johnson , Jouni Malinen Cc: ath11k@lists.infradead.org, linux-kernel@vger.kernel.org, hostap@lists.infradead.org References: From: Jeff Johnson Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Authority-Analysis: v=2.4 cv=TptzFzXh c=1 sm=1 tr=0 ts=6ab68d38 cx=c_pps a=WW5sKcV1LcKqjgzy2JUPuA==:117 a=JYp8KDb2vCoCEuGobkYCKw==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=gowsoOTTUOVcmtlkKump:22 a=ePHqwv-1doYRykRbqMUA:9 a=QEXdDO2ut3YA:10 a=OpyuDcXvxspvyRM73sMx:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTI1MDA1OSBTYWx0ZWRfX3qMJLTCwKn2I VtceoYIOUnWmAFKtMIMRbOFsP11wozCzrBpki/FDRHXsqZ2ZDyVswP27Dotc3xDL00uWigvQiwL zjbiN+uRfJpX4RLSFjqPl6aVPKydPeE8OJUTH3vaCQ8ZOq54/1dHLBd1AF5MA6Bh8kW7cztgJlN WoDo0KuojvII6/tMy1s9a+FpsY/U97DDLG3pT21/lKKnXNOx/CSKGn3Ik6chjjVY/9Dv89WQBg2 d6xq0j/L2DLr0KBwZpFEEGVM796RUZUKQAxAXF/5jIEOkboJ5rzRKpTYRlP1ez/Dys7jS8hD05B UYBIOSaf86qwPA+8AyX2FJGUbhUH2KyR9UE/brF+IcUOyX10/6FqYEevrQC2pGTMaCESRrX+TYL RaOWehZrBfCFFY26cmIaaa0X6wGpET8ja+GkLO8KwVRTwkpD63zGSgbwDV+2nsi2TdyVRJaSjTA GJ6WJh+vPfXIjivqNuQ== X-Proofpoint-ORIG-GUID: cgPvFaHTG3nG-wNzhCpQQ0HOOx2Bm-Sc X-Proofpoint-Spam-Info: AW1haW4tMjYwOTI1MDA1OSBTYWx0ZWRfX22yERoUMyL+v KhCQ+OGK5lgHLdfpj6nsjPcGOUwDae5UHuV3f4VaioIabU8wK+2urNfs6Art/ih8122P8XssE6z 2X6O3e/Skggp2aEJMLho+7mKWmmqKsE= X-Proofpoint-GUID: cgPvFaHTG3nG-wNzhCpQQ0HOOx2Bm-Sc X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-25_02,2026-09-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 phishscore=0 clxscore=1015 priorityscore=1501 impostorscore=0 malwarescore=0 suspectscore=0 lowpriorityscore=0 adultscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609250059 On 9/25/2026 7:00 AM, Alexander Wilhelm wrote: > Based on my research, DFS channels cannot be scanned passively, so I used a > sniffer to verify that the "directed" probe requests with given SSID were > actually being transmitted. In general that isn't correct. For starters, everything related to DFS is gated by regulatory rules. So the operation of the client device first depends upon whether it is configured for operation in a given country, or if it is configured for World Mode. If configured for World Mode, then initially DFS channels can only be scanned passively. A client device in World Mode must not transmit on a DFS channel unless under the control of a master device. To do otherwise violates regulatory rules in many countries. So the normal process is to perform passive scan on DFS channels and process Country elements in Beacon frames in order to determine the country in which the client is operating (aka perform an 802.11d scan). Then the client can switch from World behavior to country-specific behavior. But even when operating in country-specific mode, whether by the initial configuration or by processing Country elements, a client cannot transmit on a DFS channel unless it is under control of a master device. If a client receives a beacon on a DFS channel, then that channel is considered to be under control of the master device that sent the beacon, and only at that point can a client device actively probe/authenticate/associate. Further complicating the issue is that some regulatory bodies have rules that govern under what conditions Country elements can be used to determine the current operating country. In particular, the FCC has rules which require a device to maintain all FCC restrictions unless multiple criteria are met (I don't remember the exact rules but seem to remember that at a minimum there cannot be any master devices sending beacons with US Country elements and there must be multiple master devices sending beacons with the same non-US Country element before the device can be consider to be located in that non-US country. /jeff