You want to send a message to every user on the local subnet.
Use the UdpClient class with the appropriate broadcast address.
Broadcasts are network messages that are forwarded to all the devices on a local subnet. When a broadcast message is received, the client decides whether to discard (depending on whether any application is monitoring the appropriate port). Broadcasts can’t travel beyond a subnet because routers block all broadcast messages. Otherwise, the network could be swamped in traffic.
To send a broadcast message, you use a broadcast IP address, which is the IP address that identifies the network and has all the host bits set to 1. For example, if the network is identified by the first ...