HI i was having the same problem and I found a soultion and more importantly I explain how to do it and what could be cause it not to work.
This is what I running
iPod touch 4 generation running iOS 5 then upgraded to iOS 6
wireless internet is provided by a 2nd generation Airport extreme running in bridge mode
and connect to a Netgear DG834 which in turn connects to my ISP.
Symptoms I have on my iPod touch
▪ I can no longer connect to the Internet. when before I could using all the same router.
▪ My iPod touch see my Airport extreme but can not connect It just show a spinning cog
▪ I can connect to the internet via tethering to my mobile phone
▪ I have receive a self-assigned IP address such as one that starts with a 169, rather than one that a 192.x.x.x
Resolution
So what is happening is that when my iPod touch tries to connect to my router it could not contact the DCHP server so I had to use a static IP to get online. To do this do the following
1.Go to settings and select Wi-Fi
2. Select your Wi-Fi network
3. Press the white arrow in a blue circle next to the name of your Wi-Fi network
4. In the screen that Appears you will see a bar that has DHCP, BootP and Static choose static.
5. type in your a free IP address theses normally start 192.168.x.x if in dought go to system presence and select network and then you will see you network connections. Look for Status at the top of the window and below that it will say what you computers IP address is. It will be something like 192.168.1.4, you would type in a high number for the last digit like 19.168.1.5.
6. put in the Subnet mask normally this is 25.255.255.0
7. your routers IP address this is found from your network preferences by clicking on the advanced then on TCP/IP. It will be soothing like 192.168.0.1
8. put in the DNS setting I use OpenDNS which is 208.67.222.222
So what is cause the problem
What any device including your iPod touch needs to connect to the internet it asks the router for a what is called an IP address, this provides it with an identity so that when it connects to the router it nows who is requesting the connection. The DHCP (Dynamic Host Configuration Protocol) server in your router is the thing that assigns you your IP and makes sure that two devices do not get the same IP address.
But if the DHCP can not be contacted then your device e.g. iPod touch assigns one it self starting 169. Addresses in the self-assigned range (such as 169.x.x.x) are not routed for traffic on the public Internet. A 169 address indicates that your DHCP server is not assigning you a valid IP address or that you cannot connect to the network to receive the address.
