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Network Load Balancing (NLB)
Before we discuss the changes to NLB for Windows Server 2003, an oddity in Microsoft's support for NLB needs to be pointed out. Microsoft does not publish an HCL or catalog for NLB. Microsoft assumes that you are using server class components, because some workstation/client class
top-of-the line components, you could run into unexpected problems. For example, there are some low-end NICs that lack the necessary functionality to fully work with NLB. Yet, there are no easy
New Management UI
Windows Server 2003 introduces a management GUI for NLB cluster. The GUI can be used to create and maintain clusters.
The GUI can sometimes get
The GUI program is called NLBMGR.EXE, and a shortcut is present in the Administrative Tools menu. Care must be exercised when using both the GUI and the CLI to manage a cluster. NLBMGR.EXE does not refresh its cluster view, so if you perform a change via the CLI while it is active, it will have a stale view and will get confused. Clusters can be managed using both interfaces; however, make sure that you use only one interface at a time and whenever you use the CLI, make sure the GUI is not active.
A very common deployment scenario for NLB cluster involves a large cluster with multiple applications sharing the resources. Until Windows Server 2003, such a cluster had a big inconvenience: it had only one VIP (Virtual IP) and one set of port rules. So it was not possible to separately administer the multiple applications. In Windows Server 2003, Microsoft adds the capability to have multiple VIPs assigned to one cluster, and each VIP in
When using the GUI to configure an NLB cluster, a distinction is made between the first cluster VIP and the additional cluster VIP. However, for application purposes, there are no differences and this is just a GUI oddity.
Because each VIP is actually a separate IP address and port rule, it's possible to have each IP registered under different
NLB clusters have been designed from the beginning to use unicast IP addresses. Unfortunately, having multiple machines answer to the same IP unicast address is a misuse of the IP design ”multicast IP addresses were
Figure 13.2. Unicast warning.
In an effort to improve the usefulness of multicast MAC addresses, Windows Server 2003 NLB has been modified to support IGMP (Internet
IGMP is an IP specification used for communication between a set of computers and an upstream switch for the purpose of forming multicast groups. After the switch
With the addition of IGMP support, NLB now also generates a multicast IP address to associate with the multicast MAC address. The MAC address used by NLB can be obtained using the NLB IP2MAC command:
E:\>nlb ip2mac 184.108.40.206 WLBS Cluster Control Utility V2.4 (c) 1997-2002 Microsoft Corporation. Cluster: 220.127.116.11 Unicast MAC: 02-bf-9d-36-a0-37 Multicast MAC: 03-bf-9d-36-a0-37 IGMP Multicast MAC: 01-00-5e-7f-a0-37
The multicast IP address and the multicast MAC addresses are
IGMP support does not change anything with regard to the
Enabling IGMP support is a simple check box in the NLBMGR GUI. It is available only to clusters that use multicast MAC addresses.
Because of the history of NLB, prior to Windows Server 2003, the CLI was actually WLBS (Windows Load Balancing Service). In Windows Server 2003, both NLB and WLBS are available as CLI and have the same syntax and features. However, help still mentions only the WLBS command.
Microsoft has provided a WMI provider for NLB since Windows 2000. However, with Windows Server 2003 and the introduction of the WMIC command, WMI becomes a lot more useful. Oddly enough, NLB has two WMI providers, one that is documented and provides almost everything needed, and one that is undocumented and provides the necessary functionality for NLBMGR, which is a WMI consumer. The undocumented provider provides only one class called NLBSNIC .
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