Chapter 6 Clustering Switches

Planning a Switch Cluster

HSRP and Standby Cluster Command Switches

The switch supports Hot Standby Router Protocol (HSRP) so that you can configure a group of standby cluster command switches. Because a cluster command switch manages the forwarding of all communication and configuration information to all the cluster member switches, we strongly recommend the following:

For a cluster command switch stack, a standby cluster command switch is necessary if the entire switch stack fails. However, if only the stack master in the command switch stack fails, the switch stack elects a new stack master and resumes its role as the cluster command switch stack.

For a cluster command switch that is a standalone switch, configure a standby cluster command switch to take over if the primary cluster command switch fails.

A cluster standby group is a group of command-capable switches that meet the requirements described in the “Standby Cluster Command Switch Characteristics” section on page 6-3. Only one cluster standby group can be assigned per cluster.

Note The cluster standby group is an HSRP group. Disabling HSRP disables the cluster standby group.

The switches in the cluster standby group are ranked according to HSRP priorities. The switch with the highest priority in the group is the active cluster command switch (AC). The switch with the next highest priority is the standby cluster command switch (SC). The other switches in the cluster standby group are the passive cluster command switches (PC). If the active cluster command switch and the standby cluster command switch become disabled at the same time, the passive cluster command switch with the highest priority becomes the active cluster command switch. For the limitations to automatic discovery, see the “Automatic Recovery of Cluster Configuration” section on page 6-13. For information about changing HSRP priority values, see the “Configuring HSRP Priority” section on page 40-7. The HSRP standby priority interface configuration commands are the same for changing the priority of cluster standby group members and router-redundancy group members.

Note The HSRP standby hold time interval should be greater than or equal to three times the hello time interval. The default HSRP standby hold time interval is 10 seconds. The default HSRP standby hello time interval is 3 seconds. For more information about the standby hold time and standby hello time intervals, see the “Configuring HSRP Authentication and Timers” section on page 40-9.

These connectivity guidelines ensure automatic discovery of the switch cluster, cluster candidates, connected switch clusters, and neighboring edge devices. These topics also provide more detail about standby cluster command switches:

Virtual IP Addresses, page 6-12

Other Considerations for Cluster Standby Groups, page 6-12

Automatic Recovery of Cluster Configuration, page 6-13

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

 

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Cisco Systems 3750E manual Hsrp and Standby Cluster Command Switches