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Multiple network adapters

Updated: January 21, 2005

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

Multiple network adapters

Network Load balancing can use multiple network adapters in two different and distinct ways. The first use is to create multiple Network Load Balancing clusters; achieved by binding Network Load Balancing to each of the multiple adapters.

The second use for multiple network adapters is to use one or more adapters for handling cluster traffic, but also configure at least one adapter to be used for server management. The management adapter does not handle cluster traffic. Further information on this this second use of multiple network adapters is described below.

Multiple network adapters in unicast mode

In unicast mode, the cluster's media access control (MAC) address is assigned to the network adapter that is functioning as the cluster adapter, and the cluster adapter's built-in MAC address is not used. Because of this, host to host communication (other than Network Load Balancing heartbeat-related traffic) is not possible on the cluster adapter.

The following characteristics apply:

  • Adapters used as cluster adapters

    • The cluster IP address resolves to the adapter's cluster MAC address (which Network Load Balancing automatically generates).

    • If the cluster adapter's dedicated IP address is used, this IP address also resolves to the cluster MAC address.

    • The cluster adapter handles client-to-cluster traffic using the virtual IP address. However host-to-host traffic within the same cluster is not possible on this adapter because the MAC address for each host in a particular cluster is the same. For more information, see Address Resolution Protocol (ARP).

  • Adapter used as the management adapter

    • Network Load Balancing in not bound to this adapter.

    • This adapter's IP address resolves to the adapter's built-in MAC address.

    • This adapter handles network traffic specific to the computer, including traffic from both inside and outside the subnet in which the computer is located.

Multiple network adapters in multicast mode

In multicast mode, the cluster's MAC address is assigned to network adapters that are functioning as cluster adapters, but the cluster adapters' built-in address is retained so that both addresses are used, the first for client-to-cluster traffic and the second for network traffic specific to the computer.

This following characteristics apply:

  • Adapters used as cluster adapters

    • The cluster IP address resolves to the adapter's cluster MAC address (which Network Load Balancing automatically generates).

    • If the cluster adapter's dedicated IP address is used, this IP address resolves to the adapter's original, built-in MAC address.

    • In multicast mode, the cluster adapters can handle both client-to-cluster traffic and traffic specific to the computer, including all traffic from both inside and outside the subnet in which the computer is located.

  • Adapter used as the management adapter

    • Network Load Balancing in not bound to this adapter.

    • This adapter's IP address resolves to the adapter's built-in MAC address.

    • This adapter can be used to handle the network traffic specific to the computer, including traffic from both inside and outside the subnet in which the computer is located.

Important

  • 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.

    However, there is no restriction on the number of network adapters: Different hosts can have a different number of adapters.

Network Load Balancing handles the resolution of the cluster's IP address to its associated multicast cluster media access control address within the Address Resolution Protocol (ARP) on your router. In rare cases, the use of a multicast MAC address might not be supported by the ARP implementation on a given router. If this problem arises, the cluster will not be accessible from outside the local subnet. To correct this problem, you must create a static ARP entry within the router. Refer to the documentation for your router to determine how to create a static ARP entry. For more information, see Using a router in Network Load Balancing system requirements.

If you disable multicast support (causing the host to revert to unicast mode), Network Load Balancing automatically instructs the driver belonging to the cluster adapter to override the adapter's unique, built-in network address and to change its media access control address to the cluster's media access control address. This is the address used on all cluster hosts. You do not need to manually configure the network adapter to recognize this address. (Note that some network adapters do not support changing their media access control addresses. If you experience this problem, you must install a network adapter that does.)

Notes

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