Princeton University has published two papers detailing the problems encountered with the iPad and management of DHCP that disrupts the smooth functioning of the network. The first describes the situation while the second provides the beginnings of solutions.

In principle, a client accessing the network contacts the DHCP server to obtain the information enabling it to connect and, in this case, access the Internet. For this, it broadcasts a datagram incorporating its MAC address. For simplicity, the iPad server sends a message to him saying "I am the network interface 0:1:2:3:4:5, hire me an IP address.

A standard response from the server, if possible, is the diffusion of a tender. In other words, the server responds: "You can use the IP address 192.168.1.130 for the next six hours and if you still want to use the network, it will renew the lease within three hours." We are aware that this scheme is a simplified version of the communication that takes place between the client and server, and we have deliberately omitted some steps to focus on the problem of the iPad.

When everything goes well, the client requests a lease renewal time allotted to him and gives him the server, allowing it to continue to use the network until it disconnects itself. If the server does not receive a renewal application, he then decided that the client is disconnected and then releases the IP address which can then be assigned to another client.

The iPad violates these rules, however, since not renew its lease when in standby mode, despite the fact that it remains connected. So we end up with a tablet that uses an IP address that the server thinks it has free and possibly attributed to someone else. Concretely, this means that the iPad uses an IP without having to renew the lease is thus banned from the network without the user to understand why, since this whole process happens without his noticing it. To solve the problem, avoid self lock the screen and once you decide to turn the iPad, or put off the shelf or off the Wi-Fi Both measures are forcing the iPad to make a request to the server, thus renewing its lease.

This bug is rather surprising since it concerns not the iPhone, which uses the same OS, and it covers the basic operation of the network module. Princeton has announced that work with Apple on resolving the problem, Cupertino did not say when he would issue a patch.