[LINK] iPhones & Cisco
stephen at melbpc.org.au
Wed Jul 18 04:57:14 EST 2007
iPhones flooding wireless LAN at Duke University
By John Cox, Network World July 17, 2007
The built-in 802.11b/g adapters on several iPhones periodically flood sections of the Durham, N.C., school's pervasive wireless LAN with MAC address requests, temporarily knocking out anywhere from a dozen to 30 wireless access points at a time.
Campus network staff are talking with Cisco, the main WLAN provider, and have opened a help desk ticket with Apple. But so far, the precise cause of the problem remains unknown. <snip>
The misbehaving iPhones flood the access points with up to 18,000 address requests per second, nearly 10Mbps of bandwidth, and monopolizing the AP's airtime.
The access points show up as "out of service." For 10 to 15 minutes, there's no way to communicate with them, Miller says.
"When the problem occurs, we see dozens of access points in that condition," Miller says. The network team began capturing wireless traffic for analysis, and that's when they discovered that the offending devices were iPhones. Right now, Miller says, there are about 150 of the Apple devices registered on the campus WLAN.
The requests are for what is, at least for Duke's network, an invalid router address. Devices use ARP (Address Resolution Protocol) to request the MAC address of the destination node, for which it already has the IP address. When it doesn't get an answer, the iPhone just keeps asking.
Most of the WLAN comprises Cisco thin access points and controllers. Some older autonomous Cisco Aironet access points tend to uncover the flooding first, since they try to resolve the ARP request themselves.
But Miller's team has seen the CPU utilization on the WLAN controllers spiking as they try to process the request flood passed on to them in control traffic from the thin access points.
"I don't believe it's a Cisco problem in any way, shape, or form," he says firmly.
So far, the communication with Apple has been "one-way," Miller says, with the Duke team filing the problem ticket. He says Apple has told him the problem is being "escalated," but as of mid-afternoon Monday, nothing substantive had been heard Apple.
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