Hello @Mok_Chun_Kei,
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.
Is there any change in behavior if you reboot your Core or try unplugging and re-plugging your DAC?