Why do we need SocketOptions.SO_BROADCAST to enabl

Question

If we want to broadcast information from a socket, we need to enable SocketOptions.SO_BROADCAST. However, I don't understand why that is necessary.

My understanding is we set the packet with an broadcast address, just the same way as set a unicast address. Then we just need to send it through a regular socket. If its a UDP socket, then a UDP header will be added to that packet, and then an IP header containing the receiver's IP address (in this case is the broadcast address in the form of 192.168.255.255), and then a MAC address (FF:FF:FF:FF) is added.

I think the router will get the packet and perform the broadcast. I don't understand why we need to set the socket attribute to SO_BROADCAST.

Answer 1

"Socket semantics require that an application set the SO_BROADCAST option on before attempting to send a datagram to a base or broadcast address. This protects the application from accidentally sending a datagram to many systems."

Source

Answer 2

In most cases these calls just call the same thing in the OS. This is likely to be a restriction of your OS, not Java.