To provide failover in case of a system outage, you can use multiple servers for specific server roles. A load balancer performs the critical role of delivering load distribution and high availability across multiple servers. In addition to helping to improve performance, this also helps ensure that if one server fails, another server can continue to provide service. Office Communications Server 2007 R2 supports load balancing of the primary servers in the internal pool and the internal servers used to provide chat room support, as well as load balancing of the Edge Servers in the perimeter network that support access by external users. Before you deploy Office Communications Server 2007 R2, you should have one or more hardware load balancers in place and configured appropriately. This section provides the information to help you configure load balancers for your Office Communications Server 2007 R2 deployment.

Hardware Load Balancers

Hardware load balancers are devices that often combine an Ethernet layer 3 switch with the ability to load balance, and switch multiple streams of traffic, such as client to server, server to server, server to Active Directory Domain Services (AD DS), server to DNS, and management access to server pool. They are sophisticated devices that feature extensive monitoring capabilities; operate at multiple-gigabit levels; and generate powerful load balancing metrics that can be configured to route traffic based on such conditions as least connections on a server, the latency times of servers, weighted round robin, or weighted least connections. A load balancer exposes a single virtual IP (VIP) address to clients so that they do not directly access individual Enterprise Edition Front End Servers. A load balancer is not required to decrypt Transport Layer Security (TLS) or parse SIP messages.

General Load Balancing Requirements

An Office Communications Server 2007 R2 Enterprise pool consisting of more than one Front End Server requires a hardware load balancer. If you are deploying a Standard Edition server or a single Enterprise Edition Front End Server, a load balancer is not required. A hardware load balancer is required for arrays of Office Communications Server 2007 R2 Consolidated Edge Servers. A pool of Enterprise Edition servers configured as Directors is also deployed as an array behind a hardware load balancer for internal, external, or both types of users. These requirements are summarized in the following table.

Table 1. Hardware Load Balancer Requirements for Office Communications Server 2007 R2

Deployment Hardware load balancer

Standard Edition server

Not required.

Enterprise Pool with multiple Front End Servers


Enterprise pool with single Front End Server

Not required.

Array of Directors

Required for Enterprise pool. Not supported for Standard Edition servers.

Array of Consolidated Edge Servers


Office Communications Server 2007 R2 does not support the use of Windows Server 2003 Network Load Balancing (NLB) in any production deployments.

Destination network address translation (DNAT) is not supported for load balancing of an Enterprise pool or Communicator Web Access, but both DNAT and source network address translation (SNAT) are supported for load balancing of Edge Servers and HTTP. For details about load balancing pools, see Enterprise Edition. For details about load balancing Edge Servers, see External User Access Components. For details about load balancing Communicator Web Access, see Communicator Web Access Support. For details about Directors, see Director Component. For details about load balancing support in Office Communications Server 2007 R2, see Environmental Requirements. For details about load balancing, see Load Balancers for Office Communications Server 2007 R2in the Technical Reference for Office Communications Server 2007 R2 in the Reference documentation.