This is the situation: I have a Netgear wi-fi router which has not the option to extend the wi-fi lan and two rooms in my house where it was not possible to use computers or external hard disks due to the weak wi-fi signal in there. The other available stuff I have is an Apple Airport Extreme with the right features to extend the existing wi-fi lan.
After many different configuration tests I was not able to configure correctly the wi-fi lan to improve the signal and cover all my house. Then I decided to buy a couple of used powerline ethernet adapter for about 30.00 USD and I put one of them near the area I wanted to cover with my wi-fi lan.
Then I connected the Airport Extreme to the adapter located near the low signal area and I was able to solve my problem configuring the lan in this way:
1- I reserved a fixed IP on the Netgear router for the Airport Extreme and I added that specific IP in the DMZ list:
2- I put the Airport Extreme in the Bridge mode and chose Ethernet as data connection:
3 – I cloned the configuration of the Netgear wi-fi on the Airport Extreme. In particular I assigned to the new wi-fi lan the same broadcasting name to the main one:
4 – I restarted the Netgear router and I had a strong wi-fi signal into all my house.