Sending packets without network connection (wireless adapter)

4
votes

I have to send packets with a wifi adapter to another computer without connecting to any network, targeting Windows 7 and above. First of all, ad-hoc (as I understand) doesn't fit my needs because it requires connection.

I had two ideas:

  1. create something similar to a broadcast packet which identify networks. This can be used on wireless card

  2. send fake but valid packet and which doesn't need a specific IP/MAC address (they can be broadcasts for example).

What I use: C# with a Win7 PC and a Win7 laptop for testing the program. SharpPcap to send packets. Wireshark to check if they are arrived.

I tried the second method:

static void Main(string[] args)
{
    WinPcapDeviceList devs = WinPcapDeviceList.Instance;
    foreach (WinPcapDevice wdev in devs)
    {
        System.Console.Write("Device: ");
        System.Console.WriteLine(wdev.Description);
        foreach (var addr in wdev.Addresses)
            System.Console.WriteLine(addr.Addr);
        System.Console.WriteLine("--------------");
    }

    System.Console.Write("Select device: #");
    int selected = int.Parse(System.Console.ReadLine());
    var dev = devs[selected]; //yes, no checking for oob...
    dev.Open();

    while (true)
    {
        byte[] physBroad = new byte[] { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
        EthernetPacket etherPacket = new EthernetPacket(
            dev.MacAddress,
            new PhysicalAddress(physBroad),
            EthernetPacketType.IpV4);

        IPv4Packet ip4Packet = new IPv4Packet(
            new IPAddress(0),
            IPAddress.Broadcast);

        ip4Packet.Protocol = IPProtocolType.UDP;

        etherPacket.PayloadPacket = ip4Packet;

        UdpPacket udpPacket = new UdpPacket(
            80, //tried with different port setups
            80);

        udpPacket.PayloadData = Encoding.UTF8.GetBytes("test packet");
        ip4Packet.PayloadPacket = udpPacket;

        dev.SendPacket(etherPacket);
    }
}

Without connecting to the same network they are discarded (not arrive at Wireshark). I can only see the packets if they are on the same network.

For the first one, I know about IEEE 802.11, but I can't find anything about how to craft and send those packets. Is it possible to do this without dedicated hardware like AirPcap? I'd like to avoid writing a driver too if not necessary.

ps: I have an Edimax Wireless LAN card in my PC, and a Mediatek MT763E 802.11bgn Wifi-Adapter in my laptop. I installed the same version of Wireshark on both of them, but I can't turn the monitor mode on, and cannot set the link-layer type to IEEE-802.11, only to Ethernet and DOCSIS types.

1
c#networkingwifiwireless
Broadcast packets only work with someone (a router) to actually perform the broadcast. You can't just throw packets into the air and have something catch them. Why can't you have a network. This is impossible without one. – BradleyDotNET
Thats what I'm afraid of. It's for a contest. It is said that it should work on win7/8 without connection to a network using laptops with wifi adapters. It should work like a bluetooth system but with wireless cards. Sending ieee802.11 frames would be the best, but not on Windows. – David Szalai
Its a contest, so rules are rules, but it seems like you are basically writing the ad-hoc networking protocol. If I was doing this in industry, I would take advantage of the already existing one :). – BradleyDotNET
I'm just reading about WinPcap on Windows. Its harder than I thought, it seems I can't send/sniff wifi packets because they get converted to/from Ethernet frames, so without a full new driver (which I'm not going to finish in 2 weeks) it's impossible. – David Szalai
Probably. Sounds like a really hard programming contest to me. The best of luck to you though. WinPcap is definitely not easy to work with. I used it to send Ethernet packets, but you can't even do that without an already existing network, and it wasn't exactly simple. – BradleyDotNET

1 Answers

3
votes

Change your WiFi SSID to the message :-)

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Or this:

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