they really did us a dishonor by making us run airport utility 6, 5 was better
two ways to extend network
the regular way
check "allow network to be extended" on the host router
and check "extend wireless network' on the other router
pros
----
wireless link between units
cons
-----
can reduce throughput
works on the same channel
the ethernet method
http://support.apple.com/kb/PH5121
if you can connect the base stations with ethernet instead of wireless, is the the ethernet cable not only provides a gigabit link between your remotes, but it also allows each airport base station to be on a different channel. and even a different name , like "home" or "bedroom"
like your indoor airport extreme can be on channel 11 and 149 and your outdoor airport extreme would be on channel 6 and channel 161
another cool feature with different names and ethernet is your computer will "steer" to the strongest signal and stay connected.
the problem with extended a network over wireless is , it just does not steer.
if you walk away too far from the access point, you might have to manually reconnect to get to the closer router.
here is a good page
http://manski.net/2013/05/extending-wi-fi-networks-with-airport-express/
one other thing i want to troll about is that the wifi alliance does not test interoperability when it comes to extending networks. WDS = "wireless distribution system" is not a "standard' it is a "technology" like
how back in the modem days "k56 plex" and "v2" were "technologies" and "v.90" was a standard.
there is no "wds" standard.
so when connecting wifi access points to extend your wifi network, it is recommended that you use the same brand /make /model for the router and any extenders your using