If your AirPort Extreme is a newer "square" version with rounded corners, this model will support Apple's "extend a wireless network" feature.
Either a new AirPort Express or AirPort Extreme....or Time Capsule....could be used to "extend a wireless network" to provide more wireless coverage by connecting to your "main" AirPort Extreme using wireless only.
referring to my submission just before, you said:
" ... either a N E W Airport Xpress or.. etc.. " could be used!
That AirPort Xpress has to be "NEW"!( As I supected )- Right?
How is it defined,' NEW'? By S/N?
As I asked, how do we lnow other than by messy long trials?
Quite frustrating to me!
Thank you very much.
This AirPort Express:
It is the only Express with 2 Ethernet ports. All others are "old"
Apple does not specify a model number in their product information, but it is A1392 in the U.S. I do not know if Apple uses different model numbers in other countries.