802.11 探测请求是否包含真正的 BSSID？

Question

似乎 802.11 探测请求从不包含真正的 BSSID，而是包含通配符 BSSID（例如 ff:ff:ff:ff:ff:ff），但我似乎找不到任何说明这一点的文档。 Meraki 文档说：

"Because the probe request is sent from the mobile station to the destination layer-2 address and BSSID of ff:ff:ff:ff:ff:ff all AP's that receive it will respond."

这是否意味着探测请求从不包含真正的 BSSID？即使它们有时包含 SSID？

Answer 1

我找不到任何明确说明探测请求永远不会包含真实 BSSID 的内容。然而，在我在网上找到的所有示例中，它都设置为 ff:ff:ff:ff:ff:ff。这是 blog of a wireless network expert 的另一个案例：

Below shows the detail of Probe Request frame sent by the client which is a management type with subtype value of 4. As you can see client is sending it 6Mbps (lowest supported rate by the client). Address fields are set like below

Address Field-1 = Receiver Address (= Destination Address) ff:ff:ff:ff:ff:ff

Address Field-2 = Transmitter Address (=Source Address) 84:38:38:58:63:D5

Address Field-3 = BSSID ff:ff:ff:ff:ff:ff

此外，我自己进行了测试，但从未发现真正的 BSSID 广播。因此，虽然我不会说它永远不会发生，但它确实很少发生，因此值得考虑它永远不会出现。

Answer 2

我见过很多带有特定 BSSID 的探测请求帧。例如，在无线分布系统 (WDS) 中，一个 AP 将探测具有特定 BSSID 的另一个 AP，因为它们具有相同的 SSID：

Frame 2022: 310 bytes on wire (2480 bits), 310 bytes captured (2480 bits)
Radiotap Header v0, Length 25
802.11 radio information
IEEE 802.11 Probe Request, Flags: opmP..FT.
    Type/Subtype: Probe Request (0x0004)
    Frame Control Field: 0x41f3
        .... ..01 = Version: 1
        .... 00.. = Type: Management frame (0)
        0100 .... = Subtype: 4
        Flags: 0xf3
            .... ..11 = DS status: WDS (AP to AP) or Mesh (MP to MP) Frame (To DS: 1 From DS: 1) (0x3)
            .... .0.. = More Fragments: This is the last fragment
            .... 0... = Retry: Frame is not being retransmitted
            ...1 .... = PWR MGT: STA will go to sleep
            ..1. .... = More Data: Data is buffered for STA at AP
            .1.. .... = Protected flag: Data is protected
            1... .... = Order flag: Strictly ordered
    .101 1101 0001 0110 = Duration: 23830 microseconds
    Receiver address: 80:1d:30:a5:81:39 (80:1d:30:a5:81:39)
    Destination address: 80:1d:30:a5:81:39 (80:1d:30:a5:81:39)
    Transmitter address: 4b:3b:67:a4:4d:fe (4b:3b:67:a4:4d:fe)
    Source address: 4b:3b:67:a4:4d:fe (4b:3b:67:a4:4d:fe)
    BSS Id: ef:e1:f9:51:09:e6 (ef:e1:f9:51:09:e6)
    .... .... .... 0010 = Fragment number: 2
    0100 1110 1001 .... = Sequence number: 1257
    Frame check sequence: 0x853d68c9 [incorrect, should be 0x7089dc98]
    [FCS Status: Bad]
    HT Control (+HTC): 0x8ab91f91
    WEP parameters
Data (245 bytes)

假设你的PC加入了一个名为Starbucks的开放式无线网络，当你在家时，如果某个Rogue AP与它同名，那么你的PC就会连接到该AP。这就是为什么有些客户端实际上也允许您有选择地 select BSSID。并且在ad-hoc网络中，有很多带有特定BSSID的探测请求。

802.11 探测请求是否包含真正的 BSSID？

Do 802.11 probe requests ever contain real BSSIDs?

mac-address

bssid

wifi

access-point