Apple way to create your own DOS hardware!!Read the article from Network World and you be the judge! Hit us up in the comments!
The Wi-Fi connection on Apple’s recently released iPhone seems to be the source of a big headache for network administrators at Duke University.
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.
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“Because of the time of year for us, it’s not a severe problem,” says 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’re down, and then coming back up a few minutes later. But in late
August, this would be devastating.”
That’s because 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 10-15
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 the Address Resolution Protocol (ARP) 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.
“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,” Miller says.
Most of the W LAN is
comprised of 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 midafternoon Monday, nothing
substantive had been heard from Apple.Whatcha Think? The IT folks at Duke are trying to find out if other WLANs are having a similar problem. Any experiences to share? We are conducting experiments in our offices/labs today. Please any info to report leave it in the comments!
