How to set your router to make sure the mirror can work?
Screen Mirroring relies on being able to find Smart TVs (Roku etc.) on your home network and being able to communicate with your Smart TV (Roku etc.). At the same time, your Smart TV must also be able to communicate with your Mac. Some router settings will block this communication. For everything to work smoothly, please apply the following router settings:
Ensure you have the latest firmware update for your router on the manufacturer’s website.
If you have a dual band router, use separate names for the 2.4GHz and 5Ghz network. Then make sure that both the Mac and the TV are on the same network. So: if the Mac is on 2.4Ghz, your TV should also be on 2.4Ghz. If the Mac is on 5Ghz, put your TV also on 5Ghz.
If you have a router with MAC address filtering, add the MAC address of your TV to the list of filtered devices.
Disable Access Point/Client isolation on your router.
Disable Wireless Isolation on your router.
Disable IGMP Proxy on your router.
Disable any Virtual Private Networks (VPNs) or proxy servers, on your router and/or computer.
Enable UPnP/Multicast on your router.
Enable IGMP on your router.
Special for Netgear Nighthawk router. It turns out there is a problem with network traffic between the 2.4Ghz network and the 5Ghz network.
For optimal performance of screen mirroring with your Netgear Nighthawk dual band router, connect both your Mac and your TV to the 2.4Ghz network.
If your TV is connected through a powerline adapter. Most powerline adapters create a separate subnet, which means that your Smart TV will not be able to reach your Mac to get the screen mirroring video stream.
Please connect your TV in the same way to your router as your Mac is connected to your router.
Or if you have multiple subnets in your home network. Your Mac might be able to find your Smart TV on a different subnet, but your TV will not be able to get the screen mirroring video stream from your Mac. To fix this: please make sure that your Mac and your TV are on the same subnet.