From: Joel VanderWerf <vjoel@...>
Date: 2004-01-23T06:38:01+09:00
Subject: how to broadcast UDP packets


I'm trying to use ruby to immitate some C code that broadcasts UDP 
packets, but I can only seem to receive packets that are sent to a 
specific interface address, not to a broadcast address. Here are the 
sender and receiver:

==== sender.rb ====
require 'socket'

port = 1234

#host = "localhost"
host = "192.168.1.3"

#host = "<broadcast>"
#host = "255.255.255.255"

socket = UDPSocket.open
socket.setsockopt(Socket::SOL_SOCKET, Socket::SO_BROADCAST, true)

loop do
   socket.send("sample data", 0, host, port)
   sleep 0.1
end
====

==== receiver.rb ====
require 'socket'

port = 1234

#host = "localhost"
host = "192.168.1.3"

#host = "<any>"
#host = "255.255.255.255"
#host = ""
#host = nil

socket = UDPSocket.open
socket.setsockopt(Socket::SOL_SOCKET, Socket::SO_BROADCAST, true)

socket.bind(host, port)
p socket.recvfrom(20)
====

As the two programs are written, the receiver prints out "sample data". 
That's also the case when both programs use

   host = "localhost"

But for any combination of the broadcast hosts (e.g., "<broadcast>" and 
"<any>"), the receiver doesn't get the packet.

Any help is appreciated.