Every day this week the Clustering & High-Availability is writing about some of the top questions we get about Network Load Balancing (NLB) in Windows Server 2008 R2. We hope you find these helpful!
Software Test Engineer
Network Load Balacing
What is the maximum number of hosts that can be included in one NLB cluster?
32 is the maximum number of supported nodes. However, studies have shown that the Ideal number of nodes is 8. This is because the network traffic is broadcasted to every node, yet only one NLB node accepts the connection, so scaling beyond 8 nodes can cause a slight performance hit.
If you need a larger cluster you can you can create multiple NLB clusters, and use round robin DNS to load balance between each cluster.
Can NLB function with a single NIC per server?
Yes. Unlike previous versions, Network Load Balancing in Windows Server 2008 R2 can be configured on servers with a single network adaptor.
Can I run mixed NLB clusters containing Server 2003, 2008 & 2008 R2 hosts?
Yes, but only temporarily. NLB supports rolling upgrades only from Windows Server 2003 to Windows Server 2008 R2 and from Windows Server 2008 to Windows Server 2008 R2, during which time it is supported to have a mixed mode cluster. However you should only be in the mixed mode for the duration of the upgrade, and move all nodes to the same level as soon as possible for the best stability.
As there are new features in each version, the overall functionality of the NLB cluster is only as good as the earliest version. For example, if you have a 4 node Server 2003 cluster and you upgrade 3 nodes to Windows Server 2008 R2, you will still be at the Server 2003 functional level. This means you will not be able to load balance IPv6, use PowerShell or take advantage of the Extended Affinity timeout functionality until all nodes have been upgraded to Windows Server 2008 R2.