I have two airports, one quite old and one brand new. Which should be connected to the modem in an extended network?

Question

I just got a new airport express to extend my wireless network.  It's 802.11(n).  I have an older airport-- I don't know what iteration of the 802.11 standard.
If I connect them with Ethernet, which should be connected to the modem?  Does that answer change if I have to connect the two airports wirelessly?

Answer 1

Unless I use the WAN port on the new APE, right?
Correct. But, if you do this, the question about which device connects where is then already answered....since the "new" AirPort Express must connect to your modem. So, your best wireless performance will occur in the area near the modem. Hopefully, that is where you need the best performance.
Side note-- the tech specs linked below for the 1st gen, draft-n APE say that it, too, is dual band, although it doesn't actually seem to be.)
It's confusing since a device can be dual band, but not simultaneous dual band.
1st Gen AirPort Express (AX) is dual band because it can provide a 2.4 GHz or 5 GHz network. But, it cannot provide both at the same time. It is one or the other.
The 2nd Gen AirPort Express is simultaneous dual band because it provides both a 2.4 GHz and 5 Ghz signal at the same time.
1)  Cable Modem --->  Switch ---> Two APE (all ethernet)
2)  Cable Modem ---> 2nd Gen APE ---> 1st Gen APE  (all ethernet)
3)  Cable Modem ---> one APE ~~~> other APE (wireless between APE)
1) Will not work if you have a simple cable modem....one Ethernet port only.
If your cable "modem" is a modem/router with multiple Ethernet ports, then you could connect both AirPort Express devices back to the modem/router....and you would not need a switch at all unless you need more Ethernet ports for other devices.
2) would be correct if you have a simple cable modem
3) If you want to make use of the simultaneous dual band capability of the Express, then that device must be connected directly to the modem. The 1st Gen Express will "extend" one band only.....probably the 2.4 GHz band, since it is stronger.
If you use the 1st Gen Express connected to the modem, the "new" Express will not extend two bands. It will only extend the band that it "sees" from the 1st Gen Express, so you lose the simultaneous dual band capability of the "new" Express in this type of setup.
If you "extend"using wireless only, there is typically a bandwidth loss of about 50%, so it is always a compromise in this type of setup.