Question

I know that it is not easy to bind a port number to TCP socket that you would use to send data (because systems usually bind a random port to sockets).

But I read on one article that by using some low level networking methods you can bind a port number to a TCP socket then use it to send data ?

Does anyone has an idea about how that could be done ?

I am using c programming language

Answer 1

Bind it before connecting.

s = socket(AF_INET, SOCK_STREAM, 0);
/* ... */

memset(&client_addr, 0, sizeof(client_addr));
client_addr.sin_family = AF_INET;
client_addr.sin_port = htons(22222);

if (bind(s, (struct sockaddr *) &client_addr, sizeof(client_addr)) < 0) {
    perror("bind");
    exit(1);
}

connect(s, (struct sockaddr *) &server_addr, sizeof(server_addr));