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  1. Select 'Preferences' from the Mail menu, and click on the 'Accounts' tab from the Preferences window. Select your new account from the left hand column. Click the 'Advanced' tab and uncheck the box to 'Automatically detect and maintain account settings.' Navigate back to the 'Account Information' tab.
  2. A customer called in and explained that he needs to permanently blacklist a MAC address. He has followed the 6.4.x User Guide, and set the blacklist-time to '0' (indefinite), but the GUI and the CLI still show the blackout timer is counting down from 3600 seconds (default) for that MAC address.
  3. MAC (Media Access Control) is a unique identity to any IP devices. So, using MAC address, you can easily prevent unauthorized access to your router. MikroTik router provides various ways by which you can easily filter MAC address of any IP device and allow internet access to this device.

This article describes how the different Network Load Balancing (NLB) operation modes affect network infrastructure, and the best ways in which the network can support each mode.

Original product version: Windows Server 2016, Windows Server 2012 R2
Original KB number: 4494444

When a logical domain or a device associated with an automatic MAC address is removed, that MAC address is saved in a database of recently freed MAC addresses for possible later use on that system. These MAC addresses are saved to prevent the exhaustion of Internet Protocol (IP) addresses from a Dynamic Host Configuration Protocol (DHCP) server. How to Configure MAC Address Filtering. To set up MAC filtering on a router, the administrator must configure a list of devices that are allowed to join. The physical address of each approved device must be found and then those addresses need to be entered into the router, and the MAC address filtering option turned on.

Summary

Based on our experience, the most common issue that users encounter when they use NLB is that they are not informed enough about the technology. Therefore, the deployments and implementations usually lack some mandatory settings, or don't consider the most important factor in every network: Bandwidth consumption.

NLB can operate in any of three modes: unicast, multicast, and multicast that uses Internet Group Membership Protocol (IGMP multicast). Each of these modes has different requirements and places different demands on the network infrastructure.

Important

All of the nodes in a cluster must use the same operation mode.

The following table summarizes the requirements, advantages, and disadvantages of each mode.

NLB operation modeSpecial requirementsAdvantagesDisadvantages
UnicastNLB must be able to change the MAC adapter address.
  • Easy to configure
  • Appropriate for simple environments
  • May flood other systems with network traffic, causing performance issues (you may have to use additional hardware to resolve those issues)
  • Not appropriate for more complex environments
MulticastThe network infrastructure must use a static ARP entry and a static MAC address table entry.
  • More efficient use of bandwidth and lower risk of performance impacts than unicast mode
  • Each adapter uses its built-in MAC address
More complex to configure than unicast
Multicast with IGMPThe network switches must be capable of IGMP snooping.
  • Same advantages as multicast
  • Additional advantage of automatic configuration.
Requires that the network hardware have specific capabilities that the other modes do not need

You can configure an NLB cluster in one of three operation modes: Unicast, multicast, or IMGP multicast. All three modes work very well if your infrastructure is correctly configured. 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

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.

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In unicast mode, NLB uses the NLB MAC address to replace the original hardware MAC address of each adapter in each node of the cluster. 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 1500 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 24-port or 48-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.

To avoid a unicast flood, you have the following options:

  • Option 1: Insert a hub between the network switch and the NLB nodes. The hub uses the NLB unicast MAC address and connects to a single switch port, so the switch can correctly manage its MAC address table. The hub forwards traffic to the NLB nodes, and servers that connect to the other switch ports don't receive the extra NLB traffic.

  • Option 2: Create a separate VLAN for the NLB servers. Make sure that other subnets can reach the VLAN. This configuration isolates NLB traffic to the switch ports that are assigned to that VLAN.

Configure computers that have dual NICs in unicast mode

In some cases, you want to have two network interface cards (NICs) on your computer. If you are running Windows Server 2008 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.

Before you enable IP forwarding, you have to get the index of the Cluster NIC. On the computer that you want to configure, open a Command Prompt window and run the following command:

The output of this command lists the interfaces on the computer, as follows.

In the Command Prompt window, run the following command:

In this command, <Cluster Idx> represents the index of the cluster interface.

Sony digital voice editor for windows 10. To verify that the setting has changed, run the following command:

In this command, <Cluster Idx> represents the index of the cluster interface.

The output shows that forwarding is now enabled.

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Configure virtual environments in unicast mode

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 the virtual machine settings, select the NIC settings, and then select Enable spoofing of MAC addresses. Select OK. For more information, see Tip: Configure MAC Address Spoofing for Virtual Network Adapters.

  • If you are using VMware to run your virtual environment, refer to the VMware article Microsoft NLB not working properly in Unicast Mode (1556). 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.

Multicast

Multicast mode differs from unicast mode. Instead of changing the MAC addresses on the network adapters, NLB converts the NLB virtual IP (VIP) address to an NLB multicast MAC address. This MAC has the format of 03-BF-XX-XX-XX-XX. NLB also makes sure that the cluster's primary IP address resolves to this multicast address as part of the Address Resolution Protocol (ARP). Although the individual network adapters retain their original MAC addresses, the NLB traffic is addressed to the NLB multicast MAC address.

To support this configuration, you must configure the network infrastructure to use static ARP entries and MAC address table entries. Network switches cannot learn the NLB multicast MAC address in the course of their usual operations. If you skip the manual configuration step, the network switches may flood NLB traffic to all ports or drop packets. The network may seem to function correctly at first, but problems increase over time.

The articles that are listed in the following table explain clearly what you have to do to correctly configure your network infrastructure, based on your network infrastructure vendor. Remember that we don't maintain these articles. Therefore, we cannot guarantee that they are accurate or available. If you have any questions about these articles, please contact the appropriate vendor.

VendorArticle
VMwareSample Configuration - Network Load Balancing (NLB) Multicast mode over routed subnet - Cisco Switch Static ARP Configuration (1006525)
Cisco
  • Catalyst Switches for Microsoft Network Load Balancing Configuration Example
    If you use VSS on Cisco Catalyst, you may experience traffic issues on one of the stack nodes. For more information, contact Cisco and mention this bug (you must have a Cisco account to access the bug).
Juniper
HPEHP Switch 5500/5500G - How to implement Microsoft Network Load Balancing using multicasts on the Switch 5500 and 5500G
Dell
HuaweiExample for Connecting a Device to an NLB Cluster (Using Multi-Interface ARP)
D-LinkD-Link Layer 3 Switch Microsoft NLB in Multicast Mode Configuration Example
AvayaTechnical Configuration Guide for Microsoft Network Load Balancing (download)
H3C05-Layer 3 - IP Services Configuration Guide

Configure virtual environments in multicast mode

In a virtual environment, the network switches connect to the hypervisor host servers. In a high-availability virtual environment, a group of hypervisor hosts supports a group of virtual machines. An individual virtual machine may reside on any of the hypervisor hosts, and it may migrate to a different hypervisor host under specific circumstances. The network traffic must be able to reach the correct virtual machine regardless of which hypervisor host that virtual machine runs on.

To use multicast mode in such an environment, you have to configure the MAC address tables of the network switches so that each port that connects to a hypervisor host uses a static entry to map to the NLB multicast MAC address. For example, consider an environment that contains eight hypervisor hosts. Each hypervisor host has two network adapters, and all of the adapters connect to a switch. The MAC address table for the switch requires static entries that map each port to the NLB Multicast MAC address.

IGMP multicast

To use IGMP multicast, the network switches must be capable of IGMP snooping.

This mode is basically the same as multicast mode, except that the switches can automatically build their MAC address tables in this mode.

When you enable IGMP multicast, the NLB nodes send IGMP Join messages to the 239.255.x.y multicast address (in this address, x.y represents the last two octets of the NLB VIP). For example, if the NLB VIP is 10.0.0.1, the multicast address for IGMP Join messages is 239.244.0.1. These messages indicate the group membership of the NLB nodes. The switches use this information to configure the MAC address table.

Some of the articles that are listed in the Multicast section include the correct configuration parameters for their devices for multicast with IGMP. To verify that your equipment can support this mode, contact your hardware vendor.

Configure the NLB operation mode

From an NLB standpoint, the configuration is straightforward: Install the role, open the console, create a load-balancing cluster, select the nodes, set the NLB mode, and then set the ports and affinity.

Note

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To configure a cluster node by using NLB Manager, you must be a member of the Administrators group on the cluster node.

To configure the NLB cluster operation mode, use the following steps:

  1. In Server Manager, select Administrative tools and then select Network Load Balancing Manager.
  2. If NLB Manager does not already list the cluster, connect to the cluster.
  3. Right-click the cluster and select Cluster Properties.
  4. On the Cluster Parameters tab, select Unicast or Multicast in Cluster operation mode. If appropriate, you can also enable Internet Group Management Protocol (IGMP) support by selecting the IGMP multicast check box.

To configure the MAC addressing for NLB (which depends on the NLB mode), the most important tool is NLB IP2MAC. This tool is available on any computer that has NLB installed, and it is very easy to use. To start the tool, open a Command Prompt window and run the following command:

Configure Manual Mac Adress

In this command, <VIP of NLB> represents the NLB virtual IP address.

As the screenshot shows, you can get the MAC address for each mode easily by using this command. As an alternative, you can do your math, considering the following guidelines (the numbers correspond to the red numbers in the screenshot):

  1. In Unicast mode, the MAC address starts as 02-BF. This is followed by a series of hexadecimal codes that represent each octet of the VIP address.

  2. In Multicast mode, the MAC address starts as 03-BF. Again, this is followed by a series of hexadecimal codes that represent each octet of the VIP address.

  3. In Multicast with IGMP mode, the MAC address starts as 01-00-5E-7F. The last two parts of the address are the last two octets of the VIP address.

For more information about how to deploy and maintain NLB, see the following resources:

Third-party information disclaimer

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.

Third-party contact disclaimer

Microsoft provides third-party contact information to help you find additional information about this topic. This contact information may change without notice. Microsoft does not guarantee the accuracy of third-party contact information.

You must have enough media access control (MAC) addresses to assign to the number of logical domains, virtual switches, and virtual networks you are going to use. You can have the Logical Domains Manager automatically assign MAC addresses to a logical domain, a virtual network (vnet), and a virtual switch (vsw), or you can manually assign MAC addresses from your own pool of assigned MAC addresses. The ldm subcommands that set MAC addresses are add-domain, add-vsw, set-vsw, add-vnet, and set-vnet. If you do not specify a MAC address in these subcommands, the Logical Domains Manager assigns one automatically.

The advantage to having the Logical Domains Manager assign the MAC addresses is that it utilizes the block of MAC addresses dedicated for use with logical domains. Also, the Logical Domains Manager detects and prevents MAC address collisions with other Logical Domains Manager instances on the same subnet. This frees you from having to manually manage your pool of MAC addresses.

MAC address assignment happens as soon as a logical domain is created or a network device is configured into a domain. In addition, the assignment is persistent until the device, or the logical domain itself, is removed.

Range of MAC Addresses Assigned to Logical Domains Software

Logical domains have been assigned the following block of 512K MAC addresses:

00:14:4F:F8:00:00 ~ 00:14:4F:FF:FF:FF

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The lower 256K addresses are used by the Logical Domains Manager for automatic MAC address allocation, and you cannot manually request an address in this range:

00:14:4F:F8:00:00 - 00:14:4F:FB:FF:FF

You can use the upper half of this range for manual MAC address allocation:

00:14:4F:FC:00:00 - 00:14:4F:FF:FF:FF

Automatic Assignment Algorithm

When you do not specify a MAC address in creating logical domain or a network device, the Logical Domains Manager automatically allocates and assigns a MAC address to that logical domain or network device. To obtain this MAC address, the Logical Domains Manager iteratively attempts to select an address and then checks for potential collisions.

Before selecting a potential address, the Logical Domains Manager first looks to see if it has a recently freed, automatically assigned address saved in a database for this purpose (see Freed MAC Addresses). If so, the Logical Domains Manager selects its candidate address from the database.

With

If no recently freed addresses are available, the MAC address is randomly selected from the 256K range of addresses set aside for this purpose. The MAC address is selected randomly to lessen the chance of a duplicate MAC address being selected as a candidate.

The address selected is then checked against other Logical Domains Managers on other systems to prevent duplicate MAC addresses from actually being assigned. The algorithm employed is described in Duplicate MAC Address Detection. If the address is already assigned, the Logical Domains Manager iterates, choosing another address, and again checking for collisions. This continues until a MAC address is found that is not already allocated, or a time limit of 30 seconds has elapsed. If the time limit is reached, then the creation of the device fails, and an error message similar to the following is shown.


Duplicate MAC Address Detection

To prevent the same MAC address from being allocated to different devices, one Logical Domains Manager checks with other Logical Domains Managers on other systems by sending a multicast message over the control domain's default network interface, including the address that the Logical Domain Manager wants to assign to the device. The Logical Domains Manger attempting to assign the MAC address waits for one second for a response back. If a different device on another LDoms-enabled system has already been assigned that MAC address, the Logical Domains Manager on that system sends back a response containing the MAC address in question. If the requesting Logical Domains Manager receives a response, it knows the chosen MAC address has already been allocated, chooses another, and iterates.

By default, these multicast messages are sent only to other managers on the same subnet; the default time-to-live (TTL) is 1. The TTL can be configured using the Service Management Facilities (SMF) property ldmd/hops.

Each Logical Domains Manager is responsible for:

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Configure Manual Mac Adress
  • Listening for multicast messages

  • Keeping track of MAC addresses assigned to its domains

  • Looking for duplicates

  • Responding so that duplicates do not occur

If the Logical Domains Manager on a system is shut down for any reason, duplicate MAC addresses could occur while the Logical Domains Manager is down.

Automatic MAC allocation occurs at the time the logical domain or network device is created and persists until the device or the logical domain is removed.

Freed MAC Addresses

Configure Manual Mac Adresse

When a logical domain or a device associated with an automatic MAC address is removed, that MAC address is saved in a database of recently freed MAC addresses for possible later use on that system. These MAC addresses are saved to prevent the exhaustion of Internet Protocol (IP) addresses from a Dynamic Host Configuration Protocol (DHCP) server. When DHCP servers allocate IP addresses, they do so for a period of time (the lease time). The lease duration is often configured to be quite long, generally hours or days. If network devices are created and removed at a high rate without the Logical Domains Manager reusing automatically allocated MAC addresses, the number of MAC addresses allocated could soon overwhelm a typically configured DHCP server.

When a Logical Domains Manager is requested to automatically obtain a MAC address for a logical domain or network device, it first looks to the freed MAC address database to see if there is a previously assigned MAC address it can reuse. If there is a MAC address available from this database, the duplicate MAC address detection algorithm is run. If the MAC address had not been assigned to someone else since it was previously freed, it will be reused and removed from the database. If a collision is detected, the address is simply removed from the database. The Logical Domains Manager then either tries the next address in the database or if none is available, randomly picks a new MAC address.