NLB clusters work in affinity modes. Each refers to the way NLB load balances traffic. Single affinity refers to load balancing based on the source IP address of the incoming connection. It automatically redirects all requests from the same address to the same cluster member. No affinity refers to load balancing based on both the incoming IP address and its port number. Class C affinity is even more granular than single affinity. It ensures that clients using multiple proxy servers to communicate with the cluster are redirected to the same cluster member. No affinity is very useful when supporting calls from networks using network address translation (NAT) because these networks only present a single IP address to the cluster. If you use single affinity mode and you receive a lot of requests from NAT networks, these clients will not profit from the cluster experience since all of their requests will be redirected to the same server.
However, if you use an NLB cluster to provide VPN connections using either L2TP/IPSec or PPTP sessions, you must configure your cluster in single affinity mode to ensure that client requests are always redirected to the same host. Single affinity should also be used for any application that uses sessions lasting over multiple TCP connections to ensure that the entire session is mapped to the same server. Finally, single affinity must be used if your client sessions use the secure sockets layer (SSL) to connect to NLB servers.
Single affinity does not give the same load balancing results as no affinity. Consider the type of requests your cluster will handle before deciding on your cluster architecture.
r, „vides detailed information on the deployment of NLB clusters in the Windows Server 2003 Deployment Guide: "Deploying Network Load Balancing."
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