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Welcome!Whoh man, this is crazy.
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You have 3 DIR-865Ls?
What region are you located?
What are the distances between each of the 865Ls?
Where are all these devices located in relation to each other?
This is a new topology to me and not completely sure if it's even supported. I think you have too many bridges and really, you need to simplify this.
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I would recommend the following:
Putting the NAS and TV on a same connection for best performance and access between then using a external Gb network switch. This will help eliminate any un-necessary router processing that can impact network performances. You can even put the PC on the same switch, which would be preferred however isn't necessary. Only if you are doing a lot of large file xfers from the PC to the NAS would it be preferred.
Then you could have 1 bridged 865L connected as your bridge to the Main 865L router to provide the these clients with Internet when needed.
There are a couple of ways of doing this I think:ISP Modem>Main 865L Router<>External Gb Switch><LAN wired PC, NAS and TV to switch.
or
ISP Modem>Main 865L Router<>External Gb Switch><LAN wired NAS and TV to switch.
<>LAN wired PC to Router.
or
ISP Modem>Main 865L Router<Distance?>865 (brigde mode)><LAN wired NAS and TV to back of bridged 865L.
<>Lan wired PC to Router.
or
ISP Modem>Main 865L Router<Distance?>865 (brigde mode)><LAN wired PC, NAS and TV to back of bridged 865L.
You could even put an extra network switch on the back end of the bridged 865L if you need more LAN ports.
I would also recommend doing the following on the main 865L router:Setup DHCP reserved IP addresses for all devices ON the router. Setup/Networking. This ensures each devices gets its own IP address when turned on and connected, eliminates IP address conflicts and helps in troubleshooting.
Ensure devices are set to auto obtain an IP address.
If IPv6 is an option on the router, select Local Connection Only or Disable IPv6 options under Setup/IPv6.
Set Firewall settings to Endpoint Independent for TCP and UDP under Advanced/Firewall.
Enable uPnP and Multi-cast Streaming under Advanced/Networking. Disable uPnP for testing Port Forwarding rules. Disable IPv6 Multi-cast Streaming if IPv6 is not being used.
Turn off WISH, and WPS under Advanced.
WAN Port Speed set to Auto or specific speed? Some newer ISP modems support 1000Mb so manually setting to Gb speeds can be supported by the router. Advanced/Advanced Networking/WAN Port Speed
Set current Time Zone, Date and Time. Use an NTP server feature. Tools/Time.