Create a Cluster to Balance the Network Load, Part 2

Welcome back to our discussion of implementing Network Load
Balancing (NLB) on Windows Server 2003. In part one of this article,
we looked at what benefits NLB offers and at how it works. In this
installment, we’ll look at the actual process of creating an NLB

Basic NLB Configuration

The optimal NLB configuration is, of course, dependent on your
actual network environment. The implementation of any network
technology in a live environment should be thoroughly thought out and
carefully planned. With that disclaimer noted, looking at the basic
implementation process will give you some idea of just how easy NLB is
to setup and configure. Consider the information provided here as a
means to get you started.

You can configure an NLB cluster in one of two ways. The first is by
using the Network Load Balancing Manager; the other is by configuring
the properties of the network interfaces on the servers of an NLB
cluster directly. Of the two, I prefer the NLB Manager path, simply
because it puts all of the configuration options you need into one
place. For the purposes of our discussion here, it is also considered
the simpler method of the two.

the NLB manager main window
Figure 1

When you first start the Network Load Balancing Manager, which is
accessed from the Administrative Tools program group, you are
presented with the screen shown in Figure 1. There are three main
areas to the NLB Manager screen – the top panes are where the
available clusters (left), and the details of those clusters (right)
are shown. The bottom area of the screen displays log entries related
to the NLB configuration. An interesting note here is that the log
area of the screen only shows entries related to the NLB
configuration, such as the addition of a node to the cluster. Events
related to the operation of the actual NLB service are recorded in the
System log of Event Viewer, with a Source type of WLBS. WLBS stands
for Windows Load Balancing Service, which is what NLB was called in
previous versions of Windows.

the Cluster Parameters dialog
Figure 2

To create a cluster in Network Load Balancing Manager, right click
the Network Load Balancing Clusters object in the left pane of the NLB
Manager utility and select New Cluster. The Cluster Parameters dialog
box, as shown in Figure 2, will appear. In this dialog box you will
enter the IP address for the cluster (not the current IP address of
the system) as well as a subnet mask and domain name. The latter can
be omitted, but doing so will render the cluster only contactable by
IP address, which is probably not desirable. As you type in the IP
address, be sure to watch the value of the Network Address field
change in line with the IP address. This value, which will become the
physical (MAC) address for the cluster, is calculated in direct
relation to the IP address. This calculation is made so that a
duplicate MAC address will not appear on the network. This screen also
allows you to enable remote access to the cluster, and enter a
password to provide security for this feature.

the Cluster IP addresses dialog
Figure 3

Clicking ‘Next’ on the Cluster Parameters dialog takes you to the
Cluster IP addresses dialog. This screen allows you to enter another
IP address for the cluster. For the purposes of this exercise we’ll
assume that you only want one IP address associated with the
cluster. Clicking ‘Next’ on this screen takes you to the Port Rules
dialog box as shown in Figure 3. Port rules allow you to control
exactly what traffic can be handled through the cluster IP address. By
default, all ports are available. If you want to restrict traffic on a
port-by-port basis, you will first need to remove the default rule
before adding your own. Clicking ‘Next’ takes you to the Connect
dialog box in which you enter the IP address or hostname of the first
system that will be part of the NLB cluster. When the IP address or
hostname is entered, the system is located and all of the network
interfaces on that system are listed, as shown in Figure 4. You can
then select which interface on that system you want to include in the
NLB cluster.

network interfaces available for clustering
Figure 4

Clicking ‘Next’ again takes you to the Host Parameters dialog box,
which is where information such as the Priority and the Initial Host
State settings for the server you are about to add to the cluster can
be configured. Of the two, the Priority is the most important as each
network interface in the NLB cluster must have its own Priority
setting. If there is a conflict in the Priority setting, the cluster
will not function. The Initial Host State setting is useful if you
want to add systems to the cluster, but do not want to have them
active right away. Once you have made any changes, clicking finish
closes the New Cluster ‘wizard’, and your NLB cluster is created.

All that is left to do now is add more hosts to the cluster, which
is easily achieved by right-clicking the cluster in the left hand pane
of NLB Manager and selecting Add Host to Cluster from the action
menu. Again, dialog boxes are displayed that allow you to enter the
information needed to add the host to the cluster. When you have added
hosts to the cluster, they are displayed in the Host pane (top right)
of the Network Load Balancing Manager utility, as shown in Figure 5.

the NLB Manager Host pane
Figure 5

As simple as the preceding explanation of creating a cluster might
seem, there is really little more to the actual process than what has
been described.

After the Install

Once your NLB cluster is installed and operational, you can manage
it in one of two ways; by using the NLB Manager, or with the command
line utility NLB.exe.

Managing the NLB cluster from within the NLB Manager will provide
few surprises to anyone used to working in an MMC snap-in. Most of the
actions, such as blocking traffic from a specific host, or even the
entire cluster, are achieved by right clicking the host or cluster,
selecting Control Hosts, and then choosing an action.

NLB.exe offers a range of
options for working with clusters through short, meaningful

“NLB.exe offers a range of
options for working with clusters through short, meaningful

If you prefer to work from the command line, or want to build
cluster management commands into scripts, NLB.exe offers a range of
options for working with clusters through short, meaningful
commands. For example, to stop the entire cluster from accepting
incoming traffic, simply type NLB stop at the command prompt. There
are no prizes for guessing how to start the service up again. As with
most other command line utilities, typing NLB /? at the command prompt
will display a complete listing of the options available for the

In terms of keeping an eye on the NLB service, as mentioned
earlier, events related to the NLB service are recorded in the System
log of Event Viewer rather than in the Log area of NLB Manager. For
this reason, you should make a habit of checking the System log for
any events related to the WLBS service.

After you have installed and configured your NLB cluster, further
monitoring and maintenance should be at a minimum. Due to the
self-configuring nature of NLB, all you should have to do is reap the
rewards of increased bandwidth and fault tolerance.

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