TCP Out-of-Orders and TCP Dup ACK's on Macintosh clients w/ Exchange
Posted on 2010-08-16
I have a strange issue that I am struggling with. I recently used XenConvert to virtualize a Windows 2003 Server running Exchange 2003. It is a single server which is accessed via Mac and PC clients. Ever since I virtualized the server the Mac computers are having connectivity issues.
When I run a Wireshark capture I am seeing TCP Out-of-Order and TCP Dup ACK's. A way to clearly see this behavior and the network connectivity stall is to open up the webmail and page through e-mails. You will see the connection stall midpage. It will usually resume the connection anywhere between 5 and 5 minutes later.
This is causing problems for remote Entourage users and people accessing webmail.
Now here is the strange part: The issue only affects Mac's (and one of my Linux systems that I tested with). If you pull up webmail with Internet Explorer on a Windows PC, there are no timeouts, no stalling--everything loads just fine.
I don't THINK it's a hardware issue on the switches or server NIC as Windows has no problems, just the Mac's. I am able to copy large files via SMB from the Server to the Mac, so it seems to be localized to IIS.
We're running the most recent versions of firmware on the new server. I am going to perform all Windows updates and see if a patch may resolve this issue. Can anyone think of a possible reason as to why this would be occuring?
Thanks for any suggestions!