31

When there is a Personal Hotspot network available, it displays a chain link icon instead of the usual lock icon in the list of available networks on iOS and OS X.

Wi-Fi network selection dropdown in OS X

My question is, how does OS X distinguish these networks? Is it specified in 802.11 how hotspots broadcast their SSID's differently?

  • 5
    I gave you a + just because you made me laugh with the Exploded Rice :) – Ruskes Aug 6 '15 at 23:00
  • 2
    Sounds like an opportunity to break out wireshark/promiscuous sniffer. – cortices Aug 13 '15 at 10:25
  • I deleted my answer because apparently an iPhone personal hotspot is not an ad-hoc network. I believe there is other data identifying the network as a personal hotspot but I don't have the specifics for an answer yet. (I am fairly certain that it is not based on MAC address as @emotality suggested) – Josh Aug 23 '15 at 15:41
  • I BET there is an Apple specific IEEE802.11 Beacon Frame extension that announces tethering, like others do (e.g. Ciscos CCX). Unfortunately I have no device to test with. – Max Ried Oct 26 '15 at 20:47
7

I think this question should be posted in Reverse Engineering Stack Exchange site. You're asking for the implementation details about a black box...

In fact I did dig around a little on /System/Library/CoreServices/Menu Extras/AirPort.menu and /System/Library/Frameworks/CoreWLAN.framework/

There is a private method of CWNetwork called isPersonalHotspot, kind of:

char -[CWNetwork(Private) isPersonalHotspot](void * self, void * _cmd) {
    eax = [*(self + 0x4) objectForKey:@"IOS_IE"];
    eax = LOBYTE(eax != 0x0 ? 0x1 : 0x0) & 0xff;
    return eax;
}

It seems just checking some identifiers. I think SFRemoteHotspotDevice and WiFiXPCEventProtocol may have more low level details but I didn't check.

BTW, There is also a property to identify whether is CarPlay network

@interface CWNetwork : NSObject <NSCopying, NSSecureCoding>
... //redacted
@property(readonly) BOOL isPersonalHotspot;
@property(readonly) BOOL isCarPlayNetwork;
... //redacted

Apple controls the Hardware, the Drivers and the Operating System, I guess they can easily add extra metadata when broadcasting the WiFi signal so your Mac knows to whether adding the chain icon or not.

If anyone figure out exactly how Apple did the trick, please let me know. :)

0

The chain icon is showing that the internet connection is being bridged through another device. It is not specifically for personal hotspots.

  • Apart from the fact that Wi-Fi connections are almost always bridged to another network device, this doesn't really explain why hotspots created on Android devices do not show up with a chain icon. – user3052786 Aug 24 '15 at 22:49
  • On macOS Sierra, hotspots created using Android devices show the chain icon. – Suraj Jul 30 '17 at 11:07
-1

Apple talks to Apple, they know their own products and know when it is an Apple device or not. Apple may have their own MAC Address range or they simply see all the information there is about this device, ie:

If you go to About this Mac, System Report, Network, Wifi. You will see the following details about this network/device.

Wifi Details

Check at interfaces: Card Type, MAC Address or Locale. These can possibly be all "Apple Identifiers". When making a hotspot with your iPhone, Apple decided to share the info with your Mac to show it's an Apple device.

  • I gotta say, I really doubted that this could be a possibility at first since none of that info except MAC is shared in 802.11, but after reading into it, I'm starting to think your theory could have some merit.Apparently, the first 3 octets of a MAC address indicates the manufacturer of the device, and Apple uses a separate manufacturer portion of the MAC address on all of its iDevices. – user3052786 Aug 26 '15 at 1:35
  • Now if I could somehow spoof the BSSID of an access point so it shows up as an iDevice, I could possibly confirm or disprove this theory... Anyone know how this might be accomplished? (Or if it can be accomplished at all?) – user3052786 Aug 26 '15 at 1:37
  • Lol no I dont think its a good idea to ask hacking questions here :P but you can mark answer as correct if it answered your question. :D – emotality Aug 26 '15 at 6:35
  • I think this is not the case. Even hotspots created using Android devices show the "chain" icon. – Suraj Jul 30 '17 at 11:06
  • Where did you see this happening, Suraj Thapar? – Coroos Oct 25 '17 at 11:36
-2

Also, hotpots on iOS are identified as 172.20.10.x, as well.

  • 1
    You won't receive DHCP traffic unless you have associated with the AP. – Max Ried Oct 26 '15 at 20:54

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