Microsoft KB Archive/925476

= Network Load Balancing scenarios that are supported for use with Virtual Server 2005 R2 =

Article ID: 925476

Article Last Modified on 10/10/2006

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APPLIES TO


 * Microsoft Virtual Server 2005 R2 Standard Edition
 * Microsoft Virtual Server 2005 R2 Enterprise Edition

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INTRODUCTION
This article describes the Network Load Balancing (NLB) scenarios that Microsoft Product Support Services (PSS) supports for use with Microsoft Virtual Server 2005 R2.

You can configure Network Load Balancing in different ways in Microsoft Windows. However, when you configure Network Load Balancing for use with Microsoft Virtual Server 2005 R2, you must consider the following limitations:
 * The architectural limitations of Virtual Server 2005 R2
 * The limitations of the Virtual Machine Network Services driver



Overview
Network Load Balancing is a clustering technology that is included with Microsoft Windows 2000 Server and with Microsoft Windows Server 2003. Network Load Balancing uses a distributed algorithm to distribute network traffic across several hosts. This behavior helps enhance the scalability of certain IP-based services. These services include the following:
 * Web services
 * Virtual Private Networking (VPN) services
 * Streaming Media services
 * Terminal Services
 * Proxy services

Network Load Balancing also helps provide high availability of services by detecting host failures and by automatically redistributing network traffic to operational hosts. When you use Network Load Balancing together with Virtual Server 2005 R2, Network Load Balancing can also provide this high availability of services to virtual machine clusters.

Supported Network Load Balancing configurations for use with Virtual Server 2005 R2
The following scenarios describe the supported Network Load Balancing configurations for use with Virtual Server 2005 R2.

Scenario 1: Virtual machines are load-balanced, and the host computer acts as the client
In this scenario, all network traffic is on the same physical computer. Virtual machines are clustered by using Network Load Balancing. The host computer acts as the client.

The Virtual Machine Network Services driver loops through all the virtual machines to determine which guest operating system owns the cluster media access control (MAC) address. This loop does not immediately terminate when a match is found. Therefore, each match receives the network packet.

Scenario 2: Virtual machines are load-balanced, and a virtual machine acts as the client
In this scenario, all network traffic is on the same physical computer. Virtual machines are clustered by using Network Load Balancing. A different virtual machine acts as the client.

The Virtual Machine Network Services driver loops through all the virtual machines to determine which guest operating system owns the cluster MAC address. This loop does not immediately terminate when a match is found. Therefore, each match receives the network packet.

Scenario 3: Virtual machines are load-balanced, and a second physical computer acts as the client
In this scenario, the destination MAC address is on a separate physical computer that is running Virtual Server 2005. Therefore, the network traffic leaves the external client computer to reach the load-balanced virtual machines.

The Virtual Machine Network Services driver on the Virtual Server host computer sends the packets to each virtual machine in the Network Load Balancing cluster.

Scenario 4: Virtual machines on Host A are load-balanced, and a virtual machine on Host B acts as the client
In this scenario, the destination MAC address is on Host A. Therefore, the network traffic from the virtual machine on Host B leaves Host B through the Virtual Machine Network Services driver. Then, the Virtual Machine Network Services driver on Host A sends the packet to each virtual machine in the Network Load Balancing cluster.

Scenario 5: Network Load Balancing is configured across two or more physical host computers, and a physical computer acts as the client
In this scenario, the client computer and each Network Load Balancing instance are on different physical computers. Virtualization is not involved in this scenario. In this scenario, the Network Load Balancing cluster MAC address receives the incoming traffic and then distributes this traffic to each node in the Network Load Balancing cluster. You can expand this scenario to change any one of the Network Load Balancing nodes to be a virtual machine. Or, you can expand this scenario to change the client to be a virtual machine.

