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iPad wi-fi woes caused by dodgy DHCP

Network administrators at Princeton University say they have got to the root of wi-fi connection problems with Apple's tablet device.

Early adopters have been complaining loudly about dropped connections since the launch a week or so ago in the USA.

"Apple iPads began appearing on Princeton University's campus soon after they become available April 3 2010. On April 4, we observed our first DHCP client malfunction from an iPad," said a post on the university's web site. "Over the next few days, more iPads malfunctioned in the same way."

According to the report, the iPad uses DHCP to obtain a lease, renews the lease zero or more times, but then continues using the IP address without renewing the lease. The iPad allows the DHCP lease to expire, but it continues using the IP address after allowing the lease to expire.

"The incident continues for some time but ends when the iPad asks for a new DHCP lease, or the iPad disconnects from the network. This is a problem because it can interfere with service to others. Once the lease has expired, the DHCP server may lease the IP address to another client.

Within a few days, the folks at Princeton had seen enough incidents from the iPads already on campus to conclude that there was a problem. Roughly half the iPads had malfunctioned in the same way.

"Because the problems were so common and began as soon as the iPads arrived, we felt it unlikely that the problem was due to misconfiguration. It seemed more likely to be an issue common to the iPad/iPhone OS 3.2 platform. We collected technical data and reported the issue to Apple on April 7.

"Given the symptoms we have seen, we hope that it is due to some bug in iPhone OS 3.2 and can be addressed via a software update."

The authors of the report say that they have been able to reliably reproduce the problem by allowing the iPad to lock its screen before DHCP lease renewal time, and then allowing it remain in that state (powered on with its screen locked) until the DHCP lease has expired, assuming the iPad experiences no 802.11 wireless disconnect/reconnect events during that time.

22 of the 41 iPads on the campus have been affected by the same malfunction and the findings have been reported to Apple.