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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 6 Clustering Switches
Planning a Sw it ch Cl uster

HSRP and Standby Command Switches

The switc h supports Hot Standby Router Protocol (HSRP) so that you can configur e a group of standby
comman d s wit che s. Beca use a c om mand sw itch ma nage s the fo rwarding o f a ll c om mun icat ion an d
configuration information to all the member switches, we strongly recommend that you configure a
cluster standby comma nd switch to take over if the pr imary co mman d switch fails.
A cluster standby group is a group of command-capable switches that meet the requirements described
in the “Standby Command Switch Characteristics” sectio n o n page 6- 3. Only one cluster standby group
can be assi gn ed per clu s ter.
Note • When the command switch is a Catalyst 3550 switch, all standby command switches must be
Catalyst 3550 swit ches .
•When the command switch is a Catalyst 2950 switch running Release 12.1(9)EA1 or later, all
standby co mm and s wit che s must b e Ca talyst 2950 sw itch es ru nni ng Re le ase 12.1(9 )EA1 or l at er.
•When the command switch is a Catalyst 2950 switch running Release 12.1(6)EA2 or later, all
standby co mm and s wit che s m ust b e Ca talyst 295 0 swit ches ru nning Rel ease 1 2.1(6 )E A2 or la ter.
•When the com mand switc h is runnin g Release 12.0(5 )WC2 or ea rlier, the standby comman d
switches ca n be the se sw itches : C atalyst 2900 XL, Cata lyst 2950, and Cat alyst 3500 XL switches .
Note Th e clu ster sta ndby group i s an H SRP g rou p. D isab lin g HSRP di sable s t he c luste r stand by group.
The switches in the cluster standby group are ranked according to HSRP priorities. The switch with the
highest pri or ity i n the gr oup i s the ac ti ve com mand sw itch (AC). The switch with the next highest
priority is the standby comm and sw itch (SC) . The o ther s wit che s in the clu ster sta ndby grou p a re the
passive command swit ches (PC). If the acti ve 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 “Automatic Recovery of Cluster
Configuration” section on page 6-15. For in formation a bout chang ing HSRP priority values, refer to the
standby priority interface configur ation mode command i n the IOS Rele ase 12.1 doc umenta tion set.
The HS RP commands a re the same for changin g the prio rity of clus ter stan dby group membe rs and
router-red undan cy group mem bers.
Note The HSRP standby hold time interval should be greater than or equal to 3 times the hello tim e interval.
The de fault H SRP st andby ho ld time in terval is 10 seco nds. T he d efault HS RP s tand by hello ti me
interval is 3 seconds. For mor e informa tion ab out the sta ndby hold time and hello tim e intervals, refe r
to th e Re lea se 12.1 doc umen t ation se t on Cisc o. com.
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 comm and swit ches:
•Virtual IP Addr esses, page 6-1 3
•Other Co nsidera tions fo r C luster Sta ndby Gro ups, p age 6-1 3
•Automat ic Recovery of Cluster Configur ation, pa ge 6-15