iPhones Lead to Headaches on Duke’s Wireless Network

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Date: Tuesday, July 17th, 2007, 14:25
Category: iPhone

It’s new, it’s spiffy and damn is it cool to have.

And it’s apparently brought Duke University‘s wireless LAN system to its knees.

Writing for NetworkWorld.com, author John Cox has pointed out that anywhere from a dozen to 30 wireless access points have been overwhelmed by requests from several iPhone handsets.

At this time, campus network administrators are talking with Cisco, the campus’ main WLAN provider and have opened a help desk ticket with Apple.

“Because of the time of year for us, itβ€š’s not a severe problem,” commented Kevin Miller, assistant director, communications infrastructure, with Duke’s Office of Information Technology. “But from late August through May, our wireless net is critical. My concern is how many students will be coming back in August with iPhones? It’s a pretty big annoyance, right now, with 20-30 access points signaling they’e down, and then coming back up a few minutes later. But in late August, this would be devastating.”

The iPhones apparently flood the access points with as many as 18,000 address requests per second, consuming almost 10 megabits per second of bandwidth and overtaking the access point to the point that the access point shows up as “out of service” for up to 10 to 15 minutes at a time. During these periods, there’s no way to communicate with them.

In addition to temporarily shutting the access points down, the iPhone, through the use of the Address Resolution Protocol, will request the MAC address of a destination node since the device has already obtained an Internet Protocol address. If the device receives no answer regarding the MAC address, it just keeps asking.

Miller has stated that Duke’s network team began capturing wireless traffic for analysis and discovered that the offending devices were iPhones. There are currently about 150 iPhones registered to use Duke’s campus WLAN.

“I’m not exactly sure where the ‘bad’ router address is coming from,” Miller says. One possibility: each offending iPhone may have been first connected to a home wireless router or gateway, and it may automatically and repeatedly be trying to reconnect to it again when something happens to the iPhone’s initial connection on the Duke WLAN.

They’re still sorting out what that “something” is. On two occasions, one last Friday and one today, Monday 16 July, both users seemed to be behaving completely normally, yet both iPhones started flooding the net with ARP requests. In both cases, the user first successfully connected to the WLAN at one location, and then moved to another building, where the ARP flood began. “It may have something to do with the iPhone losing connectivity and then trying to reconnect in a new location,” said Miller.

Duke has currently commented that the trouble ticket with Apple was “escalated”, but as of now, nothing substantive has been heard from the company.

This fall could prove interesting, especially if you’re in a campus network capacity.

If you’ve seen anything along these lines or have your own stories, ideas or feedback, let us know over in the forums.

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