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The Cisco IOS  Server Load Balancing (SLB) feature allows the user to define a virtual server that represents a cluster of real servers, known as a server farm. When a client initiates a connection to the virtual server, the Cisco IOS SLB load balances the connection to a chosen real server, which depends on the configured load-balance algorithm or predictor.

An SLB switch can represent a point of failure, and the servers can lose their connections to the backbone if power fails or if a link from a switch to the distribution-layer switch is disconnected. These are the two types of redundancy features you can use to reduce that risk:

  • SLB Hot Standby Router Protocol (HSRP)

  • SLB stateful backup


In order to get redundancy to run between two SLB switches, you need to configure HSRP between the two VLAN interfaces and then associate the standby name with the Cisco IOS SLB Virtual Server (Vserver).

In some scenarios, it is seen that if the stcky timers are configured low for the client, then the connections times out soon and the client starts a new connection. Use the sticky (virtual server) command in order to configure the high value for stick timers.

Note: Currently the Catalyst 4000 / 4500 series switches does not support Cisco IOS SLB feature.

Refer to these documents for more information with sample configurations:

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