Mobile Computing

iPad Users Face Blockout on Princeton Network

• By Dian Schaffhauser
• 04/20/10

For a short period during April, Princeton University set a policy recommending that Apple iPad users not connect to the campus wireless network on threat of having their devices banned. The policy was put in place shortly after iPads began turning up on campus at the beginning of April and experienced problems accessing the network.

According to an announcement issued by the Office of IT, staff detected that the source of the problem lay with Dynamic Host Configuration Protocol (DHCP) lease renewal. DHCP allows a device on a network automatically to obtain network configuration details, including a unique IPv4 address. That lease might last for several hours and then be renewed behind the scenes by the device again. Under certain common conditions, the iPad DHCP lease would expire, but the device would continue using the same IP address. This could cause conflicts with another device that had picked up that lease to use for its network access after the initial expiration.

Princeton reported the problem to Apple's technical support, reporting to the campus community, "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."

It also posted an alert to inform iPad users that device malfunctions would result in the device being blocked from the network, "to maintain the stability and reliability of campus network services." The alert remained in place through April 19, when IT posted a workaround. Users who ignored the workaround still faced the prospect of having iPad network access curtailed on campus.

The workaround comes in three flavors: powering down the device, turning off the wireless interface through iPad settings, or taking no action at all while allowing the screen to remain unlocked. In each event, the iPad will request a new DHCP lease.

According to an update posted by the IT staff, it has "performed only limited testing of this workaround, but the results to-date have been encouraging."

However, the update warned, "It's possible that the workaround does not fully address the problem; we've only had time to perform limited testing. It's also possible that the iPad will malfunction because the customer neglects to carry out the procedure carefully--for example, by sometimes locking the iPad's screen without first turning off its WiFi interface. If a customer's iPad malfunctions, regardless of whether s/he is using this workaround, OIT will still need to block network service for the iPad, to stop it from continuing to disrupt service."