Configuring Server Load Balancing
Server Load Balancing Overview
OmniSwitch AOS Release 7 Network Configuration Guide
June 2013
page 23-7
Server Load Balancing Overview
The following sections describe SLB operational theory (see
“Server Load Balancing Cluster Identifica-
), an SLB example (
“Server Load Balancing Example” on page 23-8
), and server health
“Server Health Monitoring” on page 23-10
Note.
Alcatel-Lucent also offers link aggregation, which combines multiple Ethernet links into one virtual
channel. Please refer to
Chapter 8, “Configuring Dynamic Link Aggregation,”
for more information on
link aggregation and dynamic link aggregation, and to
Chapter 7, “Configuring Static Link Aggregation,”
for information on static (OmniChannel) link aggregation.
Server Load Balancing Cluster Identification
An SLB cluster consists of a group of physical servers, also known as a server farm. The SLB cluster
appears as one large virtual server, which is identified using one of the following methods:
•
Virtual IP (VIP)—An IP address is assigned to the cluster (virtual server). Client requests destined for
this VIP are routed (Layer-3 mode) to the servers that are members of the VIP cluster. Note that it is
necessary to configure cluster servers with a loopback interface.
•
Condition—A QoS policy condition name is assigned to the cluster (virtual server). Client requests that
meet the criteria of the policy condition are bridged (Layer-2 mode) or routed (Layer-3 mode) to the
servers that are members of the condition cluster. Note that it is
not
necessary to configure cluster
servers with a loopback interface.
Note
. See
“Configuring and Deleting SLB Clusters” on page 23-12
for more information on configuring
VIP and condition clusters.
Server Load Balancing Cluster Modes
The cluster mode refers to whether client requests are bridged (Layer-2 mode) or routed (Layer-3 mode)
by the switch to the appropriate SLB cluster. A VIP cluster only supports Layer-3 mode, so request
packets are always routed to the cluster. A condition cluster supports both Layer-2
and
Layer-3 modes.
When the Layer-3 mode is active (VIP or condition clusters), routed packets are modified as follows:
•
The source IP address is changed to the IP address for the switch router interface.
•
The destination IP address is changed to the IP address of the destined server.
•
The TTL value is decremented.
When the Layer-2 mode is active (condition clusters only), request packets are not modified and are only
switched within the same VLAN domain. The Layer-2 or Layer-3 mode is selected when the condition
cluster is configured on the switch. See
“Configuring an SLB Cluster with a QoS Policy Condition” on
for more information.