OIT Networking & Monitoring Services

Workaround for "iOS 3.2.1 - 4.0.2 Requests a DHCP Lease Too Often" Issue

iOS 3.2.1 and 3.2.2 on the Apple iPad®, iOS 4.0 and 4.0.2 on the Apple iPod Touch®, and iOS 4.0 - 4.0.2 on the Apple iPhone® behaves in a way that can degrade network service on large networks with many such devices. (A detailed description of the issue is at iOS 3.2.1 - 4.0.2 Requests a DHCP Lease Too Often.)

We have updated this workaround a number of times, as testing showed that earlier versions of this workaround were not always effective.

Princeton University reported the issue to Apple, and worked with Apple to resolve the issue.

Apple addressed this issue as of iOS 4.1. This workaround is not needed on a device running iOS 4.1 or later. iOS 4.1 was released for iPhone and iPod Touch, but not iPad. iPads obtained the fix starting with iOS 4.2.


Procedure

  1. Turn off "Push" (i.e. Microsoft Exchange ActiveSync) support for all mail, contacts, and calendar accounts. Do so using: Settings -> Mail, Contacts, Calendar -> Fetch New Data -> Push -> Off.

    Using this setting to turn off "Push" support for mail, contacts, and calendar accounts will override any per-account settings at: Settings -> Mail, Contacts, Calendar -> Fetch New Data ->Advanced.

    You may still choose to set a schedule for periodically fetching such data, using the lower portion of the Settings -> Mail, Contacts, Calendar -> Fetch New Data screen.

  2. Turn off Apple FaceTime® if the device supports it. Do so using: Settings -> Phone -> FaceTime.

    Devices which support FaceTime are: iPhone 4.

  3. If you have installed any applications which use the operating system's multitasking API to listen for incoming VoIP (Voice over IP) phone calls, remove those applications.

    (iOS 3.2.1 - 4.0.2 do not ship with any applications which do this, but some may be available from the App Store.)

  4. Turn off "Notifications" (Apple Push Notification Service). Doing so can be a little tricky, because the setting appears and disappears depending on the applications installed. Begin by checking the Settings application for a Notifications category.

    The Settings -> Notifications category appears if your device presently has any applications installed which support Apple Push Notification Service. None of the applications pre-installed in iOS 3.2.1 - 4.0.2 support Apple Push Notification, but many such applications are available in the App Store.

  5. If the "Settings" application is still running, quit the "Settings" application by single-tapping the "Home" button.

  6. Reboot the device. This is because turning off Settings -> Notifications and turning off Settings -> Phone -> FaceTime are not fully effective right away. Reboot the device as follows:

    1. Turn off the device by pressing and holding the On/Off/Sleep/Wake button for a few seconds until the red "slide to power off" slider appears on the screen. Release the On/Off/Sleep/Wake button. Drag the slider to power off the device.

    2. Turn on the device by pressing and holding the On/Off/Sleep/Wake button until the Apple logo appears on the screen. Release the On/Off/Sleep/Wake button.

  7. Be aware that when you launch any application that support "Notifications", your device may sometimes display an alert suggesting that you turn on Notifications.

    For example, it may display an alert that says: Turn on Push Notifications to Allow "ApplicationName" to Receive Sounds, Alerts and Badges along with a button to Cancel and a Settings button that launches the Settings application and enters the Settings -> Notifications screen.

    Despite frequent alerts of this nature, you will need to remember to not turn on Notifications.

  8. Be aware that if you were to delete all installed applications which support Apple Push Notication Service, the Settings -> Notifications category will disappear, and the device will forget that you turned off Apple Push Notifications. If later you were to install any application which supports Apple Push Notification Service, the Notifications category would re-appear in Settings, but would be reset to On. At that time you would need to change this setting to Off, and then reboot.

    To avoid encountering that issue, ensure you always keep installed at least one application that supports Apple Push Notification Service.

  9. Be aware that if in the future you toggle the value for Settings -> Notifications, or the value for Settings -> Phone -> FaceTime, after turning off either setting you should reboot the device, so that the changed setting takes full effect.


Caveats

We recognize that this workaround represented some inconvenience to the customer. We viewed this as a temporary workaround to allow these customers the opportunity to use their devices on the campus network until there was a fix from Apple. Apple fixed the bug as of iOS 4.1 (for iPhone and iPod Touch); the fix reached iPads starting with iOS 4.2.

This workaround involves disabling various services on the device. Naturally, any services or applications which rely on any of those features will be affected. For example, Apple's "Find My iPad", "Find My iPod Touch" and "Find My iPhone" services (available to Apple MobileMe® subscribers) are not available, because they rely on notifications (Apple Push Notification Service).


Why is this Workaround Effective?

The DHCP client software in iOS 3.2.1 - 4.0.2 can exhibit the issue when the following conditions are met simultaneously: the device is not attached to a power source, the device is attached to a Wi-Fi network, the device is asleep, and the device is not running any application which uses the operating system's multitasking API to stream audio from the network while the application is in the background, and there is no active cellular interface carrying cellular data.

This workaround is effective because it results in the device choosing to disconnect from the Wi-Fi network (typically about 10-15 seconds after the device goes to sleep) when the circumstances above are met.


Revision History

On July 9 2010, we added a step to turn off Apple FaceTime.

On July 9 2010, we added a step to remove any applications which use the operating system's multitasking API to listen for incoming VoIP (Voice over IP) phone calls.

On July 16 2010, we updated the text to note that disabling FaceTime may not be fully effective until after rebooting the device.

As our testing indicated the that July 9 revisions appear to have made the "partially effective" workaround "fully effective", on July 16 2010, we updated the text to reflect that.

On July 16 2010, we expanded this document to indicate that the workaround was necessary also for iOS 3.2.1 on iPad.

During August 11-12 2010, we updated this document to indicate that the workaround was necessary also for iOS 3.2.2 on iPad, and for iOS 4.0.2 on the iPod Touch and iPhone.

On September 8 2010, we updated this document to indicate that Apple addressed the issue in iOS 4.1, which they released for iPhone and iPod Touch. This workaround is not necessary for a device running iOS 4.1. iOS 4.1 was not released for iPad, so this workaround still remained necessary for iPad.

On November 23 2010, we updated this document to indicate that Apple's release of iOS 4.2 means that the fix is now available for iPads as well. As a fix is now available for all platforms affected by the issue, this workaround is no longer necessary for any platform.


A service of OIT Networking & Monitoring Services
The Office of Information Technology,
Princeton University
Last Updated: 5:00 pm March 16 2011