XWEB: OWA Uses Client RPC Binding Order to Establish Communication

Microsoft Exchange Server uses remote procedure call (RPC) built into Microsoft Windows NT to establish connections among the Exchange Server processes, such as connections between Exchange Server message transfer agents (MTAs), and to connect Exchange clients and Exchange Server computers in the network. Exchange Server can use RPC over named pipes, TCP/IP, NetBIOS, and IPX/SPX. When Exchange Server uses RPC, it proceeds through the list of the protocols above and establishes RPC binding. The preference order of the transports is defined by the "RPC BINDING ORDER," which by default is Local RPC, TCP/IP, SPX, named pipes, and then NetBIOS, in order of preference.

Outlook Web Access (OWA) uses the Outlook/Exchange client RPC binding order to establish RPC communications to the Exchange Server, the same way that an Exchange or Outlook client does.

RPC_Binding_Order is located in the registry key:

When you set up OWA and Exchange Server on different computers, OWA connects to the Exchange Server computer and uses the protocols listed in the binding order until it establishes communication with the server or until it runs out of protocols as described above. If OWA runs out of protocols and fails to connect you may receive the following error message: For additional information about changing the binding order, please see the following article(s) in the Microsoft Knowledge Base: