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Exchange ActiveSync and iOS 7 (déjà vu)

I should have seen this one coming. When iOS 6 was released, we had issues with IIS resource hogging, and it looks like Apple is at it again.

We’ve had intermittent outages for ActiveSync email clients, and it turns out iOS 7 may be the culprit. This is a Microsoft KB talking about issues with iOS 7 devices having trouble syncing with Exchange.

Basically, ActiveSync on the device and IIS on the server aren’t playing nicely and are trying to access files at the same time. This causes a server exceptions to be thrown back at the device. In response, iOS 7 continues to try and access the file, sometimes thousands of times before giving up.

On the server, the event log entry to look for is 4999 (MSExchange Common). We’ve got lots of these now.

A different KB, talking about general issues with w3wp.exe having high CPU load, wants me to parse my IIS log files for mobile devices that are logging large numbers of RPC calls due to issues with contact sync. I downloaded the Log Parser tool (which is a useful little command line thing that comes in handy when trying to make sense of huge log files), and ran it on my IIS logs for today. It came back with two abusive devices.

RPCCount of 123,509. That’s a lot. And definitely a sign of issues. Also, notice the device ID of both phones showing iPhone 5C; iOS 7 devices.

What the first KB doesn’t mention is that all this redundant activity will hammer the IIS service (w3wp.exe), causing it to consume memory, CPU and fill up the disk with huge IIS log files.

That’s 2GB worth of logs, in 10 hours. At its baseline, my environment produces ~200MB per day. Something is definitely flooding IIS with requests.

This will certainly cause issues, but apparently only issues with mobile devices. I’m not sure why Outlook Anywhere and OWA also aren’t, but that could be because they aren’t as dependent on the w3wp service (?). Currently, the MS recommended fix is to apply RU2 to our Exchange Boxes (2010 SP3). Apple has yet to offer a fix for their implementation of ActiveSync in iOS 7.

2 Comments

  1. nice articles

    Tuesday, September 2, 2014 at 9:38 pm | Permalink
  2. thanks for share!

    Wednesday, September 10, 2014 at 4:56 am | Permalink

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