UDP Receive Works But Not Send

Hello Again,

I recently had my Arduino bouncing UDP packets between my laptop and the Arduino (both receiving and sending). However, it seems now that I can only receive packets on the Arduino side. Therefore, I opened up the Example File > SendandRecieveUDP and changed the library to EthernetV2_0 and EthernetUDPV2_0. Then I changed the IP Address to 169.254.9.81 in both Processing and the Arduino Code. Load both up and I am able to successfully send Hello World across but no acknowledgement is received on the Processing side.

I recently updated my Mac to El Captain but I don't think that should have any effects.

Any help is appreciated as I am very new to this.

Thanks in advance!

The udp.endPacket call returns a value indicating success or failure of the packet send. Normally, this would indicate the next device en route to the destination received the packet, but if the destination device is on the same localnet, it will indicate delivery or fail.

if(udp.endPacket() == 1)
{
  Serial.println("Packet sent ok");
}
else
{
  Serial.println("Packet send failed");
}

edit: If it fails, check the IP address and subnet mask on the Mac's ethernet port.