@Daniele.Pinna Indeed, it's hard for an access point to isolate anything given that all devices share the same private network thanks to the main router. If any, isolation should be enforced by the main router firewall. And that wouldn't guarantee anything if the AP acts just as a regular switch and all the devices you want to isolate are connected to the AP too.

In more business oriented gear, you could define different WiFi networks, each with its own VLAN tag, and a VLAN compatible router would enforce the isolation as if they were completely separated networks. With consumer grade products (read: cheap) I guess it's asking too much :) 

@mocelet Thanks for the reply.

I understand that the separation between devices is certainly possible with "business-oriented" products, but practically every router that I have seen with the Guest network had the separation ...

Clearly no router I tried to use it the way I'm trying to use it myself ...

I'll try to "play" with the settings and maybe trying to use the old TP-Link Router (TD-W8770) that I used before this Archer C6

For now, thank you :-)

@Daniele.Pinna  AP isolation feature in other brands (Netgear, Asus...) works the same, they isolate WiFi guests from other WiFi guests, but they do not isolate wired connections from WiFi guests.

@mocelet 

I have tried on various routers provided by Italian internet operators (Vodafone, Tiscali, TIM etc) and certainly in a couple of Consumer Asus models ... the guest network is assigned a different subnet and is therefore isolated.

But also in this Router TP-Link it happens like this, but only if I set it as "Router", while if I set it as Access point no.

It is not to argue but only for precision :-)

@Daniele.Pinna My point exactly, only the main router (the one that access the Internet) can isolate all kind of clients while keeping Internet connectivity.

When it is working as access point, no matter the brand, there is no isolation possible because they would still communicate through the main router acting as a gateway, after all, all clients belong to the same subnet, the one of the main router.