Duke's WLAN Woes Lead to Cisco Patch

Duke University now says that widely publicized problems with its campuswide wireless network that were initially blamed on Apple Inc.s iPhone have instead been traced to a flaw in Cisco Systems Inc.s networking equipment.

And last Tuesday, after Cisco released a patch for the software that runs some of its wireless LAN controllers, the company acknowledged that the fix resulted from its investigation of the wireless access point failures on Dukes network.

According to Cisco, the softwares handling of Address Resolution Protocol traffic was flawed. Wi-Fi devices use ARP when theyre roaming between access points. But Cisco said the glitch could lead to an ARP storm, in which two or more WLAN controllers flood a network by passing massive amounts of requests back and forth.

Duke University

Duke University Thats exactly what happened at Durham, N.C.-based Duke, where about 30 Cisco-managed access points were failing under loads of as many as 10,000 ARP requests per second, according to a story published July 18 by Network World, a sister publication of Computerworld.

At first, Duke officials blamed the iPhone, which was being used by about 150 people on campus. IT administrators at the school thought that the devices built-in Wi-Fi adapters were pinging the hot spots with thousands of address requests each second.

But on July 20, Duke CIO Tracy Futhey posted a note on the universitys Web site that fingered an unspecified Cisco network issue for what she described as some minor and temporary disruptions in service.

Futhey added that there had been no recurrences of the network problems since Duke had installed a fix provided by Cisco.

Duke, Cisco and Apple have all remained mum on how the iPhone was involved, if at all. But Ciscos advisory about the software flaw hints that the iPhones being used at Duke may have innocently triggered the ARP storm. The Apple device constantly scans for available access points unless its Wi-Fi feature is turned off.

The flaw itself isnt innocent, though. Cisco warned that it could be used to cause denial-of-service attacks on networks.

Copyright © 2007 IDG Communications, Inc.

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