His Issue isn't with the default gateway or with the WAN port it's with the additional smart hubs that he is using for Wi-Fi extension.
BT will not offer support for these devices, as they are not recommended, and you will not be able to update the firmware on any of them.
plus having 5 smart hubs in one location will cause wifi congestion and isn't recommended.
Complete Wifi is the way forward here for what you are trying to achieve as it is designed for this very setup.
This setup will work fine if it is configured properly. Unfortunately, everyone is a Sunday afternoon mechanic in IT these days and it is not something to be doing when you clearly have no idea.
Firstly, for this set up to work properly, the ones actings as wireless access points (WAPs) need to have different channels to each other, 1, 6 or 11. Ignore the channels in between. Similarly, the 5GHz need to be separate channels, 36, 40, 44 or 48. That way they don’t interfere with each other.
Secondly, the only way to keep them all up to date is to rotate which one gets to play router. The easiest way to do this is to export the configuration file for each one. As the configuration is locked to each router you will end up with three files for the three acting as WAPs and three more for the three actings as a router.
Next time an update appears, (and we must be due one, as the last, 43.01, is now four months old), you need to reconfigure one of the WAPs to act as the router and swap it for the present router. When that updates you need to reconfigure it back to the WAP setup and reconfigure the next WAP to act as the router. Put that on and let it update. Swap it out again reconfigure it back to the WAP and reconfigure the original hub to act as a router and put it back on again. I’d give it at least 24 hours between each rotation, as if you are on FTTC this amount of swapping around will screw with DLM and temporarily drop your connection speed.
While I agree with Licquorice’s point, I would also agree with TECHNO’s, complete Wi-Fi is going to be easier if you don’t understand what you are playing with.
Edit:
As far as the disconnecting goes, that’s one of the main differences between a mesh system, like Complete Wi-Fi, and what you are trying to do, which is known as Wireless Roaming.
The different channels ensure the wireless points do not interfere with each other. Your devices will lock on to whichever channel they see as strongest at the time they connect, irrespective of what the channel is or where the device is. However, if the thing he is playing Roblox on is mobile & he is moving around with it , it will keep dropping as it switches to the next strongest signal. With mesh systems you don’t get this dropping and reconnecting.
Yes however attempting this may interrupt, Digital Voice provisioning and if there is any fault with the broadband may cause difficulty accessing the system BT end as they use a system called home view to access the smart hub , the AI will not work correctly if you are swapping the hub all the time and may cause problems with connective and throughput.
I say this is achievable but not recommended and seems like going all around the house to get a service that BT already offers at a similar cost and is guaranteed.
Oh, I'd agree there are better ways of doing it but I'm a very occasional wireless user as the network is fully wired. How I come to have three SH2's is a bit of a long story but I've been using all three in rotation since they switched me to DV, 18 months ago & no problems.
I've not had occasion to use BT support. (From what I read on here, they seem to be mainly sales people rather than tech support today anyway). I take it you speak from insider knowledge of how the AI that supports the connection works?
Well, let's just say I know a guy who knows a guy who knows a guy who is very high up in the BT\EE tech teams.
The complete Wi-Fi package takes advantage of the AI of the smart hub 2 to distribute the bandwidth evenly. However, this will not be achieved using multiple hubs in this way, as each hub will be trying to regulate the bandwidth on each device. You are more likely to have a daisy chain happening on the network.
I strongly advise you to seek guidance on a complete WIFI package with 3 extender discs. You can also use a cable to connect to the Wi-Fi discs, but that's optional.
You will also have a free home tech expert who is network-trained to attend to set the disc up for you.
If you contact BT and ask for this package and ask for the loyalty team they will help you switch. trust me it's not worth the head each doing what you are trying to do.
I am network-trained, mate…and a whole lot more besides.
Anyway, it’s not me you need to convince, but the OP. As I said, on some aspects I would agree with you.
(Love the bit about the 'AI' in the Smart hub, by the way).