Extreme Networks ExtremeWare 7.7, Command Reference Manual

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ExtremeWare 7.7 Command Reference Guide 493
9
SLB Commands—“i” Series Switches
Only
This chapter discusses server load balancing (SLB) and flow redirection commands.
SLB distributes client requests transparently among several servers. The main use for SLB is for web
hosting (using redundant servers to increase the performance and reliability of busy websites).
You can use SLB to manage and balance traffic for client equipment such as web servers, cache servers,
routers, and proxy servers. SLB is especially useful for e-commerce sites, Internet service providers, and
managers of large intranets.
SLB also provides health checking. Health checking allows you to actively poll nodes to determine their
health. The switch makes new connections only if the virtual server and node are both enabled and
passing health checks. The switch considers a virtual server or node active unless a health check fails. If
a health check fails, the switch considers the virtual server or node inactive. A virtual server or node is
also considered inactive if it is disabled and has zero active connections.
Flow redirection overrides routing decisions to transparently redirect client requests to a target device
(or group of devices). Unlike SLB, you do not duplicate content on the target device(s).
The switch can only redirect traffic that crosses a VLAN boundary, because flow redirection operates at
layer 3. Flow redirection examines traffic and redirects it based on the following criteria, in order of
priority:
1 Destination IP address and mask
2 Layer 4 port
3 Source IP address and mask
You can use flow redirection for the following:
• Web cache redirection
• Policy-based routing