Solve WiFi timeout for Apple devices

最近換了router，結果所有的Apple裝置都上不了網，反而Windows好得很。查了半天原來是Apple不支援舊的wifi，只要把2.4G wifi模式設定成只用802.11g/n就好了。 Recently changed to a new ISP and new router. All of sudden, all the Apple devices (Mac, iphone, ipad) cannot connect to internet. Using ping to a DNS (eg, 8.8.8.8), it turns out that the requests are all timeout. However, Windows didn't have this problem. Tried changing wifi channel didn't help at all. It turns out Apple doesn't support old wifi mode. So just changing 2.4G wifi mode from "b/g/n" to "g/n" solves this issue.