Hsrp And Standby Command Switches - Cisco WS-C3550-12G Software Configuration Manual

Planning a Switch Cluster

HSRP and Standby Command Switches

The switch supports Hot Standby Router Protocol (HSRP) so that you can configure a group of standby
command switches. Because a command switch manages the forwarding of all communication and
configuration information to all the member switches, we strongly recommend that you configure a
cluster standby command switch to take over if the primary command switch fails.
A cluster standby group is a group of command-capable switches that meet the requirements described
in the
can be assigned per cluster.
Note •
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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 command switch (AC). The switch with the next highest
priority is the standby command switch (SC). The other switches in the cluster standby group are the
passive command switches (PC). If the active command switch and the standby command switch become
disabled at the same time, the passive command switch with the highest priority becomes the active
command switch. For the limitations to automatic discovery, see the
Configuration" section on page
"Configuring HSRP Priority" section on page
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 3 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 hello time intervals,
see the
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 command switches:
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Catalyst 3550 Multilayer Switch Software Configuration Guide
5-12
"Standby Command Switch Characteristics" section on page
When the command switch is a Catalyst 3550 switch, all standby command switches must be
Catalyst 3550 switches or Catalyst 2950 switches running Cisco IOS Release 12.1(6)EA2 or
later.
When the command switch is a Catalyst 2950 switch running Cisco IOS Release 12.1(6)EA2 or
later, all standby command switches must be Catalyst 2950 switches running Cisco IOS
Release 12.1(6)EA2 or later.
When the Catalyst 2950 command switch is running Cisco IOS Release 12.0(5)WC2 or earlier, the
standby command switches can be these switches also running Cisco IOS Release 12.0(5)WC2 or
earlier: Catalyst 2900 XL, Catalyst 2950, andCatalyst 3500 XL switches.
"Configuring HSRP Authentication and Timers" section on page
"Virtual IP Addresses" section on page 5-13
"Automatic Recovery of Cluster Configuration" section on page 5-13
"Considerations for Cluster Standby Groups" section on page 5-14
5-13. For information about changing HSRP priority values, see the
23-6. The commands are the same for changing the
Chapter 5 Clustering Switches
5-3. Only one cluster standby group
"Automatic Recovery of Cluster
23-8.
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