How do you do this with most consumer devices? The only AP I've seen do it successfully is the AsusWRT series - Media Extender mode seems to be transparent. If I try it with anything else I'll end up with two seperate networks, e.g. 192.168.8.0/24 connected to 10.1.1.0/24 (I actually have a GL.inet AR750S in this configuration right now)
If you can wire the 2 AP via a LAN, then this is how I've used cheap consumer wifi APs which are usually combo AP+router devices:
The first AP is connecting to internet gateway through its WAN port. This AP does the networking stuff like DHCP, NAT, etc.
The other wifi APs are configured to be AP-only, i.e. disable DHCP. Use same wifi SSID and auth settings as the first AP. Then connect the APs using their LAN ports.
Client devices should now connect to the AP with the best signal.
But if the client is already connected to an AP and a better-signal AP is available, many clients won't automatically connect to the better AP. This is because the client don't know that the other AP is the same network. So if you move around you may need to trigger the client to disconnect and reconnect.
This can be solved with APs that have a "mesh" feature which can instruct connected clients to reconnect to a better AP in the same network using https://en.wikipedia.org/wiki/IEEE_802.11k-2008 but AFAIK mesh systems from different manufacturers aren't interoperable.
