Interestingly my (older) 802.11g Airport Extreme stalled today. No 802.11g client could pick it up and even though it is plugged into the LAN port of the 802.11n Airport Extreme, the Airport Utility could not “see” it.
So unplugged it, left it for about ten seconds, and switched it back on again, no worries.
This is an occassional problem, which is in the main just annoying, but I wonder what the underlying problem is (if any) and if the base station will one day just stop working for good!