Network Load Balancing (NLB) - Client Affinity and Port Configurations

Normally web applications are used by multiple users and there is a need to maintain the state of a user’s session within the web application. Each visitor connected to the web application will have their own session and a session encompasses all the requests from a single visitor within a specified period of time.

Sessions help to maintain user related variables and by maintaining the state of sessions, the application can ensure the user can complete a set of actions, like online shopping using a shopping cart application. Client affinity can be configured in Network Load Balancing (NLB) which helps in maintaining application sessions. Client affinity uses a combination of the source IP address and source and destination ports to direct multiple requests from a single client to the same server. Three types of affinity settings can be configured in Network Load Balancing (NLB).

• None: Multiple requests from the same client are not redirected to the same server by Network Load Balancing (NLB)

• Single: Multiple requests from the same client IP address should be redirected to the same server by Network Load Balancing (NLB)

• Class C: Multiple requests from the same Class C address range are redirected to the same server by Network Load Balancing (NLB). Class C affinity is useful for clients that use multiple proxy servers to access the cluster.

The three filtering modes available are

• Disabled: No filtering.

• Single Host: Direct traffic to a single host.

• Multiple Hosts: Distribute traffic between the Network Load Balancing (NLB) cluster servers.