Philip, I've noticed a problem with iDevices and smartphones where they lock up the network due to IP address duplication.
The problem usually manifest itself as slow or no wan/LAN access. This may be the problem you are having.
It seems that iDevices in particular a habit of retaining DHCP leases long after the lease has expired (e.g. When the device has left the LAN).
The solution is to statically assign the dhcp address in your router's DHCP table. I've resolved lockup problems at home, work and on one of our customers sites by doing this.
Here's some background on the problem.
http://www.imore.com/ipad-properly-r...lems-Princeton
Interestingly, the article says it shouldn't be a problem on home networks, I've found it is, at least in my case. I reserve IP's in the DHCP table for all my known devices on my home network.