Open Radar

 
Summary:
After waking a 21.5″ late 2012 iMac from sleep, the wifi network connects correctly; however, internet connectivity is not present. iOS devices on  the same network connect to the internet without a hitch, as do Windows machines and OS X machines running other OS versions.

Steps to Reproduce:
1. get a 21.5″ late 2012 iMac 
2. connect it to the internet via PPoE via a 802.11n wifi network
3. ensure you have internet connectivity
4. send the iMac to sleep
5. wait 30 seconds
6. wake the iMac from sleep by pressing a keyboard key
7. wait for the wifi to connect

Expected Results:
Internet connectivity is restored

Actual Results:
Internet connectivity is not present: networked applications like Dropbox complain about missing connectivity, Mail.app goes into offline mode, web browsers will not load pages

Regression:
This issue manifested itself immediately after upgrading from OS X 10.10.2 to 10.10.3 on an otherwise unchanged hardware and network configuration

Notes:
Changing the IPv6 setting in advanced network preferences will restore connectivity after a few seconds of delay. The actual setting is irrelevant: whatever it is set to, the above issue will occur on the next wake, and a change to any other value will restore connectivity. Other quickfix network solutions (toggling wifi, renewing the DHCP lease, defining a new network profile) have no effect.