NLB can also direct all traffic to a designated single host, which is called the default host. NLB allows all of the computers in the cluster to be addressed by the same set of IP addresses, and it maintains a set of unique, dedicated IP addresses for each host. For load-balanced applications, when a host fails or goes offline, the load is automatically redistributed among the computers that are still operating.
When it is ready, the offline computer can transparently rejoin the cluster and regain its share of the workload, which allows the other computers in the cluster to handle less traffic. NLB is useful for ensuring that stateless applications, such as web servers running Internet Information Services IIS , are available with minimal downtime, and that they are scalable by adding additional servers as the load increases.
The following sections describe how NLB supports high availability, scalability, and manageability of the clustered servers that run these applications. A high availability system reliably provides an acceptable level of service with minimal downtime.
To provide high availability, NLB includes built-in features that can automatically:. Scalability is the measure of how well a computer, service, or application can grow to meet increasing performance demands. For NLB clusters, scalability is the ability to incrementally add one or more systems to an existing cluster when the overall load of the cluster exceeds its capabilities.
To support scalability, you can do the following with NLB:. Balance multiple server load requests from the same client or from several clients across multiple hosts in the cluster. Enable high performance and low overhead through a fully pipelined implementation. Pipelining allows requests to be sent to the NLB cluster without waiting for a response to a previous request. Specify the load balancing behavior for a single IP port or group of ports by using port management rules. Define different port rules for each website.
If you use the same set of load-balanced servers for multiple applications or websites, port rules are based on the destination virtual IP address using virtual clusters. Direct all client requests to a single host by using optional, single-host rules.
Tuesday, May 26, AM. Hello tip:check network card driver version sorry my english. Network Card driver version inter I Wednesday, May 27, AM. Wednesday, May 27, PM.
NLB configured in unicast mode. Please suggest. Saturday, May 30, AM. Hello All, Can anyone give suggestion. Monday, June 1, AM. Parvez, NLB can be somewhat tricky to configure.
But there are a few problems with it, like these: NLB in Unicast mode causes a well know issue called 'switch-flooding'. Some low-budget L3 switches do not support NLB in unicast mode. NLB in unicast mode is not supported on VMware.
Multicast is required, unless you configure a work-around. This is why a second NIC is required for communication. This is why you get a warning when you open NLB manager. I don't know you scenario, but allow me to ask a few questions: You added this to the High Availability Cluster forum. You don't, right? If you are using VMs; On which Hypervisor are you hosting them?
Before you configure, please move the VMs to the same host before you configure it, so they are connected to the same vSwitch. However, serious problems can develop if you haven't prepared your network infrastructure to support the mode that you are using. Each mode has different implications for the network infrastructure. Unicast is the simplest operation mode to configure.
In theory, you don't have to do anything else in your network infrastructure. In actuality, you may have to modify the infrastructure to manage network traffic. Because multiple adapters now have the same address, any physical switches in the network can no longer correctly maintain their MAC address tables. Because they cannot determine which traffic goes to which switch port, the switches start sending all traffic to all ports to make sure that the traffic reaches its destination.
This is known as a unicast flood scenario. A unicast flood can seriously affect the network performance. In addition to the regular network traffic, every NLB node sends out a heartbeat packets each heartbeat packet contains about bytes of data. By default, a node sends a heartbeat packet each second and waits for five of those packets to be received until it considers the node as converged.
In a unicast flood situation, any switches rebroadcast this heartbeat traffic to all switch ports just like the regular network traffic. For example, if your network has a port or port switch, and only two of those ports connect to NLB nodes, the switch may end up broadcasting significant network traffic to 22 or 46 servers that don't need it. Option 1: Insert a hub between the network switch and the NLB nodes.
The hub forwards traffic to the NLB nodes, and servers that connect to the other switch ports don't receive the extra NLB traffic. Make sure that other subnets can reach the VLAN.
In some cases, you want to have two network interface cards NICs on your computer. If you are running Windows Server or later, you must enable IP forwarding on the NICs in order to ensure that traffic gets routed properly. IP forwarding is enabled by default in earlier versions of Windows. On the computer that you want to configure, open a Command Prompt window and run the following command:. By default, the virtual switches in virtual environments usually prevent unicast flooding.
For more configuration information, see the following resources:. If you are using Hyper-V to run your virtual environment, open the Hyper-V management console. Select OK. This article explains how to configure the virtual network infrastructure.
Remember to contact VMware if you have questions about their documentation. If you are using another virtual environment such as XenServer or VirtualBox and you are experiencing similar issues, contact the manufacturer for guidance.
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