The unholy trio

Are you having weird issues with connectivity? Outlook clients not being able to connect to Exchange? RDP suddenly stops working? Perhaps one of the following:

• When you try to connect to the server by using a VPN connection, you receive the following error message:
Error 800: Unable to establish connection.
• You cannot create a Remote Desktop Protocol (RDP) connection to the server.
• You cannot connect to shares on the server from a computer on the local area network.
• You cannot join a client computer to the domain.
• You cannot connect to Microsoft Exchange Server from a computer that is running Microsoft Outlook.
• You can only connect to Web sites that are hosted on the server or on the Internet by using a secure sockets layer (SSL) connection. In this scenario, you cannot connect to a Web site that does not use SSL encryption.
• You experience slow network performance.
• You cannot create an outgoing FTP connection from the server.
• The DHCP Server service crashes.
• Clients experience slow domain logons.
• Network Address Translation (NAT) clients that are located behind Windows SBS 2003 experience intermittent connection failures.
• You experience intermittent RPC communications failures.
• Clients that are configured as SecureNat clients may be unable to connect to the Internet.
• Some Outlook clients may be unable to connect to Exchange. 
• You cannot run the Configure E-mail and Internet Connection Wizard successfully.
• Microsoft Internet Security and Acceleration (ISA) Server blocks RPC communications.
• Clients cannot visit the http://companyweb Web site.
• You cannot browse Internet Information Services (IIS) Virtual Directories. 

 If you are seeing strange behaviors with networking, you ought to educate yourself and read the following:;EN-US;927168

  If any of that looks vaguely familar, you may want to consider disabling TCP Chimney, along with RSS (receive side scaling) and TCP Offloading.

As an addendum to this post, if you are having issues with CAS servers, IMAP/POP, and slow Autodiscover, you may also want to look at and apply