Sending a message to a local network broadcast via UDP

Question

I made a question about P2P connection, then with one of the answers the question arose: How to send a message on a local network via UDP in style broadcast, without a specific recipient?

With this I would like the following solutions:

• How to find a possible recipient using UDP in style Broadcast?
• How to send messages via UDP?
• What is the logic behind the "style" Broadcast and how it is done using UDP protocol.

If possible with an example in C#.

Answer 1

One of the ways to understand how UDP works is by comparing it to TCP.

TCP

• Connection: To use the TCP protocol you need to establish a connection with one (and only one) host remote.
• Bi-directional communication: Once the connection is established, the two points can send messages (which is why IP tunneling works)
• Point-to-point: A connection involves only two points.
• Guaranteed transmission: Once a package has been sent to a remote host, the protocol monitors the delivery (or warns about failures).

UDP

• Unconnected: You do not establish connections when emitting UDP packets; you only specify a target.
• Unsecured: The protocol does not implement any kind of guarantee that the package will reach the target host.
• Masking: A package can be sent to multiple hosts at the same time when the target is a mask.

In the example below, an UDP package sent to the address 192.168.1.255 from the host 192.168.1.15 will be received by all the hosts of the subnet, inclusive 192.168.1.15; The Octet .255 equates, in general terms and in the given example, to 'all hosts under 192.168.1'.

Example of UDP package issuance (in C#):

static void SendUdp(int srcPort, string dstIp, int dstPort, byte[] data)
{
    using (UdpClient c = new UdpClient(srcPort))
        c.Send(data, data.Length, dstIp, dstPort);
}

SendUdp(11000, "192.168.1.255", 11000, Encoding.ASCII.GetBytes("Olá, eu sou o Goku!"));

The above example sends to all hosts of the current subnet and port 11000 a UDP package.