ZyXEL Communications XS3800-28, User Manual, Page: 339 / 789

Chapter 46 NLB
XS3800-28 User’s Guide
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46.1.2 What You Need to Know
NLB
Network Load Balancing (NLB) is a feature developed by Microsoft. NLB enhances the performance
reliability for critical applications by sharing traffic with multiple servers in a cluster using TCP/IP protocol.
Each server of a cluster tackles a copy of a traffic. You can create a cluster by grouping up to 32 servers
together.
If a server in a cluster fails, traffic will be redistributed to the other operating servers. When the server is
back in service, it will join the cluster automatically and share the traffic.
Unicast Mode
NLB replaces the real MAC addresses of the servers in a cluster with a unicast MAC address. Each server
uses the same unicast MAC address, and a switch cannot map the unicast MAC address to a port. This
forces a switch to flood traffic meant for the cluster to all ports of the switch to make sure the traffic is
forwarded to the right destination.
The servers in a cluster cannot communicate with each other, because they use the same unicast MAC
address.
Multicast Mode
NLB assigns a multicast MAC address to the servers in a cluster. Therefore, each server has two MAC
addresses, the real MAC address and the multicast MAC address.
Create static ARP entries on a switch for the servers, so the switch will only forward traffic to the servers of
the cluster.
The servers in a cluster can communicate with each other, because they keep their real MAC address
and already have their own IP addresses.
46.2 IP Configuration
Use this screen to view and configure the IP and MAC address mapping of a cluster for layer-3
forwarding. You should use the MAC address added in the
SWITCHING > NLB > MAC Forwarding screen.
Click SWTICHING > NLB > IP Configuration to display the screen as shown.
Note: The settings configured in the SWITCHING > NLB > IP Configuration and NETWORKING >
ARP Setup > Static ARP screens cannot duplicate.