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UDP broadcast DataAvailable does not fire
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Author:  tjerk [ Mon Dec 31, 2012 5:53 am ]
Post subject:  UDP broadcast DataAvailable does not fire

Using the trial of RealSoftware I am trying to create an application that sends broadcast UDP message to check for available devices on a network.
This works fine as long as devices are in the same range. But somehow the DataAvailable event does not fire for data from other IP ranges.

netIf = System.GetNetworkInterface(cboInterfaces.ListIndex)
UDPSocket1.NetworkInterface = netIf
UDPSocket1.Port = 30718

UDPSocket1.Write(UDPSocket1.BroadcastAddress, DecodeHex("00") + DecodeHex("00") + DecodeHex("00") + DecodeHex("F6"))

DataAvailable event:
data = UDPSocket1.Read()
txtLog.AppendText(data.Address + Chr(13))

Connection directly from my PC to the device:
Sending from to
I only receive the echo from in RealSoftware
Wireshark however does show the response from the device: to

Tested this with other applications, they do receive the device message in this configuration.

If i put my PC in the network and the device in the same network it works as expected, however I need this application to find unkown devices to be able to give them an IP address.

Please help.. If this works I'll certainly buy the pro version.

Author:  tjerk [ Mon Dec 31, 2012 6:07 am ]
Post subject:  Re: UDP broadcast DataAvailable does not fire

Think I found the issue. When sending data for the first time the Windows Firewall pops up and I grant access. Only it seems that it also needs access to Public networks (although Windows does not show a message for that).

How can I force a request to the Windows firewall to make sure also messages from other IPs will be received?

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