IPad WiFi works only with WPA/TKIP, not WPA2/AES

Question

My iPad (like so many others) stopped connecting to my Linksys WRT54G router (which like everyone else's connects fine with every other device, including non-iOS 4 iPhones). The whole reset/restart/restore dance with the iPad/router/cable modem was performed to no avail. By sheer desperation, security protocols were changed, and that's what finally worked.
The protocol to the rescue was WPA/TKIP, curiously enough. (When security is completely disabled ("Open"), the iPad also connects, perhaps expectedly.) The culprit is WPA2/AES (even AES+TKIP). Any iteration of WPA2/AES ends up blocking the iPad from getting the appropriate IP address via DHCP. Once I changed to WPA/TKIP, everything's been rock-solid and fast.
(The only times WPA2/AES worked was when the iPad was first used for a couple days, and a couple days after switching back to WPA2/AES when it started working with WPA/TKIP. Since then, switching back to WPA2/AES no longer works, even temporarily.)
Any idea why initially WPA2/AES worked, and then suddenly stopped?

Answer 1

Ralph Landry1 wrote:
That is a very interesting question ... [involving] the combination of the router and the iPad and their respective implementations of the AES encryption algorithm. The AES algorithm is considerably more complex than TKIP. Why some have problems and not others has to be related to the router and its implementation and the Apple implementation.... t works fine for me connecting with [both] a Verizon FiOS (Actiontec) router [a]nd ... an AirPort Extreme. But there have been a number of posts recently about problems with Linksys and Belkin connectivity.
Tell me about it. I'd been pulling my hair out prior to "discovering (by accident," as George Costanza would say) that WPA/TKIP fixed the problem, and seems to be working fine and fast. Now I'm just academically frustrated (better than actually frustrated) wondering why WPA2/AES is so problematic +with this particular trifecta+ (my iPad, my Linksys router, and WPA2/AES).
Bottom line is there is probably not an easy solution ... and since you do have a strong security protocol that works, keep using it. Very strange that there would be a change in connectivity after a few months, though. Old engineering philosophy, if it ain't broke, don't fix it. If you have something that works, stick with it for now.
Actually, WPA2/AES worked on two (short but notable) occasions:
a) for two days when I first unpacked the iPad, and
b) for two days when I switched back to WPA2/AES upon discovering WPA/TKIP fixed the issue.
So it wasn't two months, which makes more sense. I agree with you that I'm not touching this arrangement for now. What I did have to do was change over the other devices (PCs, Wii's, TiVo's) that didn't automatically adjust over to WPA/TKIP. (To its credit, the iPhone did that on the fly.) Going through each device hurt a little, knowing I was using a less-than-optimal protocol for just one cranky device at expense of every other one--but of course I'd rather everything play nice than be necessarily cutting edge. (It's not like I'm the Pentagon or anything here.)
But also give feedback to Apple:
http://www.apple.com/feedback/ipad.html
Done and done. And thanks for a great and reassuring explanation.
Message was edited by: TashTish