Can 2 Airport Extremes remain connected to each other using their LAN ports ?

To clarify the question and scenario, one of my friend describes a typical scenario wherein he has 2 AEs. AE1 has an ISP in it's WAN port and AE2 has another ISP in it's WAN port. Can this 2 AE's remain mutually connected to each other by ethernet cable using LAN ports in both AE1 and AE2 ? He says this might be achievable if AE2 is kept in bridge mode, without using the ISP attached to it's WAN port. I simply failed to understand how this can be achieved. Seeking your help friends.

Thank you

Update :

I asked my friend what is he trying to achieve. He says the objective is, the 2 AEs remain connected individually to 2 different ISPs in their respective WAN ports, and the 2 AEs remain connected to each other by ethernet.

a) Do the AEs connect to each other LAN port -> LAN port or LAN port to WAN port ?

b) Since the 2 AEs have their own individual gateways setup, is it possible to setup an architecture wherein the 2 AEs remain connected to each other with their 2 individual ISP and if one of the ISP goes down with AE1, it can be configured through Airport utility so that traffic reaching it is diverted to the AE2, since AE1 and AE2 is mutually connected by ethernet ?

Is this type of configuration possible at all, and if the answer is yes, how ?

Thank you

Dear Bob,

Just to clear up :

This is what I get from Airport Extreme Specs :

- Gigabit Ethernet WAN port for connecting a DSL modem, cable or Ethernet network.

Does this imply that whenever 2 Airport Extremes connect to each other directly by Ethernet cable it has to be a LAN port at one end and a WAN port at the other end ? Can they also connect LAN port -> LAN port in any configuration ?

Thank you

Hello Bob,

Always nice communicating with you. In your explained reply, if the 2nd AE is kept in bridge mode and it connects to the 1st AE through one it's LAN port(keeping the WAN port free), can a person still keep the WAN port connected to the 2nd ISP(Although the ISP is defunct) ? Wanting to know if situation demands, through Airport Utility change the mode from 'Bridge' to 'Share a Public IP address', do a reboot of the 2nd AE and Voila the 2nd ISP comes up. Then go back to the 1st AE and turn it down to 'Bridge mode', users connecting to 1st AE again gets Internet through the 2nd ISP connected to the 2nd AE, this is all done manually(maybe I am daydreaming after all ...)

Thank you

Dear Bob,

Now I am really confused, does this mean what you said earlier as 'Impossible'

has turned out to be a possibility now ?

Thank you