Hello @Paul_Leach,
Welcome to the forum! So we can better assist you, please provide a brief description of your current setup using this link as a guide.
Make sure to describe your network configuration/topology, including any networking hardware currently in use, so we can have a clear understanding of how your devices are communicating.
You can also give the Help suggestion that @ged_hickman1 mentioned a try, if you input your IP address of the Core or the multicast broadcast IP of 255.255.255.255 this may help with the connection.
If this works, please let us know the networking gear in use as there may be further suggestions we can try there as well.