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Network Load Balancing key features

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Network Load Balancing key features


  • Load balances requests for individual TCP/IP services across the cluster.

  • Supports up to 32 computers in a single cluster.

  • Load balances multiple server requests, from either the same client, or from several clients, across multiple hosts in the cluster.

  • Fully pipe-lined implementation ensures high performance and low overhead.


    • During packet reception, the Network Load Balancing fully pipe-lined implementation overlaps the delivery of incoming packets to TCP/IP and the reception of other packets by the NDIS driver. This increases the overall processing speed and reduces latency because TCP/IP can process a packet while the NDIS driver receives a subsequent packet. It also reduces the overhead required for TCP/IP and the NDIS driver to coordinate their actions, and in many cases it eliminates an extra memory copy of packet data. During packet sending, Network Load Balancing also enhances throughput and reduces latency and overhead by increasing the number of packets that TCP/IP can send with one NDIS call. To achieve these performance enhancements, Network Load Balancing allocates and manages a pool of packet buffers and descriptors, that it uses to overlap the actions of TCP/IP and the NDIS driver.

High Availability

  • Automatically detects and recovers from a failed or offline computer.

  • Automatically balances the network load when hosts are added or removed.

  • Recovers and redistributes the workload within 10 seconds.


  • You can manage and configure multiple Network Load Balancing clusters and the cluster hosts from a single computer using Network Load Balancing Manager.

  • You can specify the load balancing behavior for a single IP port or group of ports using port management rules.

  • If you use the same set of load balanced servers for multiple applications or Web sites, by using virtual clusters you can define different port rules for each Web site based on the destination virtual IP address.

  • Using optional single-host rules, you can direct all client requests to a single host, in effect using Network Load Balancing to route client requests to a particular host running specific applications.

  • You can block undesired network access to certain IP ports.

  • You can enable Internet Group Management Protocol (IGMP) support on the cluster hosts to control switch flooding when operating in multicast mode.

    Layer 2 switch, HTTP get request, NLBS cluster
  • Network Load Balancing logs all actions and cluster changes in the Windows event log.

  • Using shell commands or scripts, you can remotely start, stop, and control Network Load Balancing actions from any networked computer that is running Windows.

Ease of use

  • Network Load Balancing is installed as a standard Windows networking driver component.

  • Network Load Balancing requires no hardware changes to enable and run.

  • Network Load Balancing Manager allows you to create new Network Load Balancing clusters and configure and manage clusters and all of the cluster's hosts from a single remote or local computer. Ideally you should use a second network adapter when managing the cluster from a local computer.

  • Network Load Balancing lets clients access the cluster with a single logical Internet name and virtual IP address (also know as the cluster IP address) while retaining individual names for each computer. Network Load Balancing allows multiple virtual IP addresses for multihomed servers (although in the case of virtual clusters, the servers do not need to be multihomed in order to have multiple virtual IP addresses).

  • Network Load Balancing can be bound to multiple network adapters allowing you to configure multiple independent clusters on each host. Support for multiple network adapters is different from virtual clusters in that virtual clusters allow you to configure multiple clusters on a single network adapter.

    NLB hosts and HTTP get requests
  • You do not have to modify server applications to run in a Network Load Balancing cluster.

  • If a cluster host fails and then is subsequently brought back online, Network Load Balancing can be configured to automatically add that host to the cluster. The added host will then be able to start handling new server requests from clients.

  • You can take computers offline for preventive maintenance without disturbing cluster operations on the other hosts.

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