Gets the broadcast address of an IP address


#1

Hi Ruby communauty. I am trying to broadcast a message using UDPSocket
on destination port 10000. My code is:

client = UDPSocket.new
client.connect Socket.gethostname, 10000
client.setsockopt(Socket::SOL_SOCKET, Socket::SO_BROADCAST, true)
client.send data, 0

But my packet is not a broadcast, its address is the same as my host:
192.168.0.101

In order to do so on the external interface of my system (named en0), I
had remplaced this:
client.connect Socket.gethostname, 10000
by this:
client.connect “192.168.0.255”, 10000

And now this is working. But is there a way to get automatically the
“192.168.0.255” address thanks to a Ruby method? I know I can get my IP
with IPSocket.getaddress(Socket.gethostname) but I don’t see any way to
gets its broadcast address.

Thanks


#2

On Sat, Feb 28, 2009 at 11:12 AM, Eleanor McHugh
removed_email_address@domain.invalid wrote:

… But is there a way to get automatically the
“192.168.0.255” address thanks to a Ruby method? I know I can get my IP
with IPSocket.getaddress(Socket.gethostname) but I don’t see any way to
gets its broadcast address.

The simplest way to do it is to use a regex to change the last term in the
quad:

IPSocket.getaddress(Socket.gethostname).gsub!(/.\d{1,3}$/, ‘.255’)

Simple but not necessarily correct :slight_smile:

http://learn-networking.com/network-design/how-a-broadcast-address-works

FWIW,


#3

On 28 Feb 2009, at 16:20, Sai Hl wrote:

192.168.0.101
my IP
with IPSocket.getaddress(Socket.gethostname) but I don’t see any way
to
gets its broadcast address.

Thanks

The simplest way to do it is to use a regex to change the last term in
the quad:

IPSocket.getaddress(Socket.gethostname).gsub!(/.\d{1,3}$/, ‘.255’)

Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net

raise ArgumentError unless @reality.responds_to? :reason


#4

Eleanor McHugh wrote:

On 28 Feb 2009, at 22:49, Hassan S. wrote:

The simplest way to do it is to use a regex to change the last term
in the
quad:

IPSocket.getaddress(Socket.gethostname).gsub!(/.\d{1,3}$/, ‘.255’)

Simple but not necessarily correct :slight_smile:

<http://learn-networking.com/network-design/how-a-broadcast-address-works

True, but I’m not sure the general case is so easy on the eye ;p

This is messier than it should be, but:

require ‘ipaddr’
n = IPAddr.new(“192.168.0.101/24”)
p n | (~n.instance_variable_get(:@mask_addr) & IPAddr::IN4MASK)

Or maybe you could just broadcast to the all-ones address
(255.255.255.255)


#5

On 28 Feb 2009, at 22:49, Hassan S. wrote:

The simplest way to do it is to use a regex to change the last term
in the
quad:

IPSocket.getaddress(Socket.gethostname).gsub!(/.\d{1,3}$/, ‘.255’)

Simple but not necessarily correct :slight_smile:

<http://learn-networking.com/network-design/how-a-broadcast-address-works

True, but I’m not sure the general case is so easy on the eye ;p

subnet_mask = [ 255, 255, 255, 0 ]
IPSocket
.getaddress(Socket.gethostname).split(’.’).zip(subnet_mask).collect { |
(i, m)| ((~m) & 255) | i.to_i }.join(".")

Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net

raise ArgumentError unless @reality.responds_to? :reason


#6

Brian C. wrote:

This is messier than it should be, but:

require ‘ipaddr’
n = IPAddr.new(“192.168.0.101/24”)
p n | (~n.instance_variable_get(:@mask_addr) & IPAddr::IN4MASK)

Or maybe you could just broadcast to the all-ones address
(255.255.255.255)

Yes, I had use the broadcast address :wink:
Finaly it’s simple and efficient. But I think I will try your first
solution after to.

Thanks