Alright,
I updated to 8 last night, as in India it came last night and I am facing the same problem. Now I have sorted it out, I don't know if this will work permanently or if its just a temporary solution
1st Solution : -
Go to Settings
Select Wifi
Select your network
Then select 'i' right beside the the wifi symbol of your network
See the IP address and under that see DHCP
Now go to STATIC (3rd option) and see if the contents are the same as DHCP
If, yes then reset the network settings and fill it again
If, no then write it down somewhere and copy it.
Then click on Renew Lease
When, prompted, Click Renew Lease ?
OR
Forget your network
Once your 3g/LTE is on,
Turn it off
Re-join the network.
OR
Connect your Iphone to your PC/Mac
Go to Itunes
If you have taken backup previously before updating to iOs 8
Click on Restore BACKUP
Please press Restore backup and not Iphone
The old settings would also restore and this should help.
Thanks
Smit