It seems that every time Apple squashes one DHCP bug in iOS, another one pops up.
Dynamic Host Configuration Protocol (DHCP) is a system of automatically assigning IP addresses on a network, which mostly happens behind the scenes and without users noticing anything about it. Without an IP address, a device such as an iPhone, iPad, or any sort of computer cannot access the network.
DHCP uses a “lease” system where a computer can use a specific IP address for a certain length of time. In contrast to a static addressing scheme (where each device has a permanently-assigned IP address), DHCP allows many more devices to use the network — as long as they are not all online at the same time.
Initially, iOS devices had two different problems. First they would hold on to their IP addresses after the “lease” expired, when they were supposed to be done with them.
Apple apparently fixed that problem, but created another one: devices were asking to renew their DHCP leases too often. The latter problem was fixed in iOS 4.1, but that was only released for iPhone and iPod touch devices, not iPads. With iOS 4.2, that bug is finally fixed.
But don’t get too excited.
According to Princeton’s tech team, the latest versions have a problem that they’re listing as “iOS 4.1 – 4.2.1 Allows DHCP Lease to Expire, Keeps Using IP Address.” Does that sound familiar? It’s eerily like the earlier report from Princeton, “iPhone OS 3.2 on iPad Stops Renewing DHCP Lease, Keeps Using IP Address” — so the issue is not taken care of yet.
If you only use your iOS device on a small home or office network, you may not be aware of this flaw, but — and I hate to have to be so obvious, but a lot of people have apparently missed this — managing a computer network on a university campus is a whole lot different than your home Wi-Fi network.
Despite reports, Princeton has not “banned” iOS devices, but their workaround includes disabling Notificatons, Find My iPhone/iPad, FaceTime, and removing all VoIP applications.
Hopefully one of these days, Apple will figure out how to get the iOS DHCP client to work efficiently on larger networks. In the meantime, you can keep track of the issue on Princeton’s Apple iOS Networking page.
Princeton and iOS DHCP still not getting along originally appeared on TUAW on Sun, 19 Dec 2010 09:00:00 EST. Please see our terms for use of feeds.
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