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By default, all cluster network traffic is handled by the host with the highest host priority (lowest numeric value) among the current members of the cluster. This host handles all of the cluster network traffic. If the highest-priority host fails or goes offline, the host with the next highest priority will take over the traffic. This default behavior ensures that Windows NT Load Balancing Service (WLBS) does not affect cluster network traffic for ports that you do not specifically manage with the WLBS load-balancing mechanisms. It also provides high availability in the handling of your cluster network traffic.
To maximize control of various types of TCP/IP traffic, you can configure how each port's cluster network traffic is handled.
The method by which a port's network traffic is handled is called its filtering mode. There are three possible filtering modes:
Multiple Hosts Filtering Mode:
This mode automatically distributes the port's network traffic to multiple hosts within the cluster, according to a load percentage that you specify. This load balances the network load among the hosts within the cluster and scales the performance of the Internet server programs. Network traffic is distributed among the hosts on a per-connection basis for TCP (or on a per-datagram basis for UDP), where the combination of source and destination IP address and port numbers determines a unique client request. If the host fails, WLBS automatically redistributes network traffic among the remaining hosts.
You can control the precise load-balancing behavior of this filtering mode by indicating that all hosts should maintain an equal load distribution or by setting the load percentage for each host. When you specify load percentages, WLBS adds up the load percentages for all participating cluster hosts and directs the proportional amounts to each host. The total load percentage for the cluster need not add up to 100 percent. For example, if the cluster has two hosts with load percentages of 30 and 60 percent, WLBS will direct one-third (30/90) of the traffic to one host and two-thirds (60/90) to the other host.
In addition, you can select one of three options for client affinity. This is used in handling client sessions to ensure that all network traffic from a particular client be directed to the same cluster host. When you select None, WLBS load balances all network requests across the cluster without respect to their source to maximize the scaled performance achieved by load balancing. You can select Single affinity to direct all client requests from the same IP address to the same cluster host. You can also select Class C affinity to direct all client requests from the same class C address range to the same cluster host. Increased affinity enhances the cluster's ability to support client sessions, although it may somewhat reduce scaled performance.
Single Host Filtering Mode:
This mode directs all of the port's network traffic to the host with the highest handling priority. In this mode, you specify a set of priorities for handling the port's network traffic in the event of a host failure. This lets you assign the network traffic for different host ports to different hosts in the cluster and customize the failover policy for each port.
Disabled Filtering Mode:
This mode blocks all traffic to a port to provide a firewall against unwanted network access to a cluster. However, we do not recommend that you use WLBS port rules as a firewall because you may run out of rules quickly. The maximum number of port rules that you can configure is 32.
For your convenience, you can specify that a filtering mode apply to a numerical range of ports. You do this by defining a port rule with a set of configuration parameters that define the filtering mode. Each rule consists of the following configuration parameters:
NOTE: Rules for a single port are encoded as a range having the same starting and ending port numbers.
To create a new port rule and add it to the list of rules:
To edit an existing rule:
The rules entered on each host in the cluster must have matching port ranges, protocol types, and filtering modes. If WLBS detects an inconsistent rule among the hosts in the cluster, it records a message in the Windows NT System Event Log. When this happens, consult the System Event Log to determine the host in question and which rule was disabled; fix it, and restart WLBS on this host.
Article ID: 198496 - Last Review: February 21, 2014 - Revision: 2.1
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