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Cisco EtherSwitch Service Modules Feature Guide
Information About the Cisco EtherSwitch Service Modules
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Cisco IOS Release 12.2(25)SEC
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 Command Device Characteristics” section on page 21. Only one cluster
standby group can be assigned per cluster.
Note If the switch cluster has a Cisco EtherSwitch service module, Catalyst 3750 switch, or
switch stack, that switch or switch stack must be the cluster command switch.
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 29. For information about changing HSRP priority values, see the Catalyst 3750 Switch
Software Configuration Guide, Cisco IOS Release 12.2 at
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3750/index.htm. 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 Catalyst 3750 Switch Software Configuration
Guide, Cisco IOS Release 12.2 at
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3750/index.htm.
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 in Clusters, page 28
• Other Considerations for Cluster Standby Groups, page 28
• Automatic Recovery of Cluster Configuration, page 29