User Manual

Enterasys X-Pedition User Reference Manual 341
Load Balancing
Adding Servers to the Load Balancing Group
Once a logical server group is created, you specify the servers that can handle client requests. When
the X-Pedition receives a client request directed to the virtual server address, it redirects the request
to the actual server address and port. Server selection is done according to the specified policy.
To add servers to the server group, enter the following command in Configure mode:
Notes:
• Do not use an IP address for load-balancing that is already configured for VRRP.
Session Persistence
Load balancing clients connect to a virtual IP address which, in reality, is redirected to one of
several physical servers in a load balancing group. In many web page display applications, a client
may have its requests redirected to and serviced by different servers in the group. In certain
situations, however, it may be critical that all traffic for the client be directed to the same physical
server for the duration of the session; this is the concept of session persistence.
When the X-Pedition receives a new session request from a client for a specific virtual address, the
X-Pedition creates a binding between the client (source) IP address/port socket and the
(destination) IP address/port socket of the load balancing server selected for this client. Subsequent
packets from clients are compared to the list of bindings: if there is a match, the packet is sent to the
same server previously selected for this client; if there is not a match, a new binding is created.
How the X-Pedition determines the binding match for session persistence is configured with the
persistence-level option when the load balancing group is created (see Creating the Server Group
on page 340).
There are four configurable levels of session persistence:
• TCP persistence: a binding is determined by the matching the source IP/port address as well as
the virtual destination IP/port address. For example, requests from the client address of
134.141.176.10:1024 to the virtual destination address 207.135.89.16:80 is considered one
session and would be directed to the same load balancing server (for example, the server with
IP address 10.1.1.1). A request from a different source socket from the same client address to
the same virtual destination address would be considered another session and may be directed
to a different load balancing server (for example, the server with IP address 10.1.1.2). This is
the default level of session persistence.
Add load balancing servers to a
specific server group.
load-balance add host-to-group <ipaddr/range> group-
name
<group name> port <port number> [weight
<weight>]
Add range of load balancing servers
to a range of server groups.
load-balance add host-to-vip-range <range> vip-range-
name
<range name> port <port number> [weight
<weight>]