Need Advice on Router/Double NAT Situation With Sky Max and TP link EX75

[JimM1]

@Dunc1 And finally for you some heavy bedtime reading from a down to earth well practiced and all about wireless approach.

www.wiisfi.com

[Danny11616]

@Dunc1 No problem at all. I even scratched my head for a solid 10 minutes before I was able to get it working and I work with networking and computers on a daily basis but when you know these things now you can then pass this onto the next person that needs help. 

I have seen your double NAT question and I can confirm that no you will not get double NAT because if you only use the TP link deco this will be the hub/ router if that makes sense. You will only get double NAT if you use the sky hub and the tp link deco together. 

[Eoin5]

Hi @Dunc1 👋 

I am curious of what setup you used in the end. I am struggling with this also. I have a deco x20 system with sky broadband hub. Ideally I would like to bypass the sky hub and connect the deco directly into the ONT. Did you achieve this? Thanks Eoin

[Dunc1]

Hi @Eoin5 

Yeah, it took a bit of messing around, but here’s what we did to get around the Deco/Sky/30-media issue:

1. Turned off Wi-Fi on the Sky Max — This stopped the Sky hub from trying to interfere or double-NAT with the Deco.
2. Limited the Sky router’s DHCP range —  dropped the IP address range on the Sky Max down to something like .1–.20, just to give the Deco some space.
3. Set the Deco’s IP range to start at .21 —  adjusted the Deco’s DHCP to use .21–.250, keeping it out of the Sky Max’s way and avoiding conflicts.
4. Enabled DMZ on the Sky router — Then  pointed the DMZ directly at the Deco’s static IP address, so all traffic just passed straight through without getting firewalled or filtered.
5. Made sure the Deco had a fixed IP —  assigned the Deco a manual/static IP address on the Sky side (e.g. .21) so the DMZ rule always targeted the right device.
6. Disabled UPnP on the Sky router — Not essential, but worth doing if you’re seeing port mapping issues.
7. Restarted everything in the right order — Sky router first, wait until fully up, then power up the Deco to let it pull its settings cleanly.

After that, the Deco took full control of the internal network and started behaving properly — and media devices like 30.media stopped falling out randomly.

Let me know if you need the exact IP ranges or want a diagram — happy to draw it out.

Cheers,

Dunc

[Chrisee]

@Dunc1 & @Eoin5 while I think that list is sensible I would point out a potential issue with point 6 

The Sky Max hub allows Sky to use a system called MAP-T to share an individual  IP4 addresse between 8 customers achieving the same outcome as CGNAT. This upsets UPNP so the hubs are shipped that feature disabled. If you enable UPnP we are told that switches the address sharing off going the other way turns it back on. This address sharing only impacts a few applications so it may not affect you but it is something worth remembering.

Rereading the post above the changes to the DHCP ranges are not required as the Sky hub's DHCP server has no part in assigning iP addresses to any device connected to the second router.