Apple’s Iphone a big headache for Duke University |
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. “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. Duke University reports that they’re losing communications with several of their wireless network’s APs, all of which are in the same general local. After some initial troubleshooting, the staff has decided the problem is due to an unusual quirk of the iPhone.It appears that the iPhone is broadcasting MAC address requests at a rate of 18,000 per second, which has the potential to overload all of the APs within range of the iPhone. Apparently the iPhone is requesting the MAC address of the last known gateway device whose IP address it has stored. If the contacted AP is unable to resolve the address, it will not respond. The iPhone then continues to send requests for the MAC address creating the DoS situation. If the iPhone moves out of an affected AP’s coverage area, the AP almost immediately returns to normal operation. Duke University is using Cisco equipment and has opened help tickets with both Cisco and Apple. Also they are interested in learning if any other universities or large scale wireless networks are experiencing similar circumstances. |