Differences between Windows NLB unicast and multicast

Windows NLB (Network Load Balancing) is a load balancing technology that Windows $ Server begins to provide on the operating system. NLB uses a distribution algorithm to distribute load balancing across multiple hosts, increasing the scalability and availability of key IP-based services such as the WEB, virtual private networks, streaming media, Terminal Services, proxies, and so on, while detecting host failures and automatically reallocating traffic to other operations masters. Thus providing high availability.

Windows NLB has two modes, unicast and multicast, and the two modes have different principles.

1. In unicast mode, the NLB service will re-assign the MAC address to the NLB-enabled NIC in each node (this MAC address is called the cluster MAC address), and all NLB nodes use the same MAC address (both use the cluster MAC address). NLB also modifies the source MAC address in all sent packets, which causes the switch to not bind the cluster MAC address to a port. NLB that works in unicast mode can operate in all network environments (best compatibility);

2. In multicast mode, NLB does not modify the NLB node's MAC address for the NLB-enabled network adapter, but instead allocates a two-tier multicast MAC address for NLB-specific traffic (this MAC address is called the cluster MAC address), This allows the NLB nodes to communicate with their original private IP address.

Suggestions:

NLB node server has only one NIC, use multicast mode.

If the NLB node server has multiple network cards, or if the network devices (such as layer two switches and routers) do not support multicast mode, you can use unicast mode.

Differences between Windows NLB unicast and multicast