Single network adapter in unicast mode

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

Single network adapter in unicast mode

This model is suitable for a cluster in which ordinary network communication among cluster hosts is not required and in which there is limited dedicated traffic from outside the cluster subnet to specific cluster hosts.


  • Only one network adapter is required. It is not necessary to install a second adapter.

  • This is the most straightforward configuration because unicast mode is the default.

  • This model works with all routers.


  • Ordinary network communication among cluster hosts is not possible.

  • Network Load Balancing itself does not affect network performance and a second network adapter is not a requirement. However, under certain conditions, a second adapter can improve overall network performance. For more information, see Multiple network adapters.

Regardless of the number of network adapters you use and how the adapters are configured, the cluster heartbeat traffic always originates from the network load balancing network adapter.


  • Network Load Balancing does not support a mixed unicast/multicast environment within a single cluster. Within each cluster, all network adapters in that cluster must be either multicast or unicast; otherwise, the cluster will not function properly.

    There is no restriction on the number of network adapters that can be bound to network load balancing on each computer: Different hosts can have a different number of adapters, but you can never have more than one adapter on a computer be part of the same cluster.

    Different adapters on each computer can be part of different clusters, and they can all reside on the same subnet. You can also host multiple clusters on the same network adapter. For more information, see Understanding virtual clusters.

  • Before you install Network Load Balancing, it is vital that you review Checklist: Enabling and configuring Network Load Balancing, including the sections on cluster parameters, host parameters, and port rules. It is highly recommended that you read through these sections before configuring Network Load Balancing.

For more information, see also Single network adapter and Single network adapter limitations.