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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 6 Clustering Swit ches Planning a Switch Cluster

Automatic Recovery of Cluster Configuration

The act ive comman d switch con tinua lly forward s cluster-con figuration i nformat ion (but not
device-configurat ion info rmation) to the standby comma nd switch. This ens ures that th e standby
command switch can take over the cluster immediately after the active command switch fails.
Automatic discovery has these limitations:
•This l imi tatio n a ppli es o nl y to c luster s th at have Catalys t 2950 an d C ata ly st 3550 c omm an d and
standby comm and swit ches: If the active command swit ch and standby comm and swit ch becom e
disabled at th e same ti me, the passiv e co mman d switc h with th e h ighest pri ority bec omes the a ctive
comman d s wit ch. H owever, because it was a p assive standby com ma nd sw itch , t he previous
comm an d s witc h did not forward cluster-configuration information to it. The active command
switch only forwards cluster-configurat ion informa tion to th e standby comm and swit ch. You must
therefore rebuild the cluster.
•This limitation applies to all clusters: If the active command switch fails and there are more than
two switches in the c luster standby grou p, the new command switch doe s not discover any
Catalyst 1900, Ca talyst 2820, a nd Catalyst 2916 M XL memb er switches. You must re-add these
memb er swi tch es to th e clu ster.
•This limitatio n applie s to al l clus ter s: If th e act ive command switch f a ils and bec om es active again,
it does not disc over any Catalyst 1900, Ca talyst 2820, an d Catalyst 2916 M XL memb er switch es.
You must again add these member switches to the cluster.
When the previously active command switch resumes its active role, it receives a copy of the latest
cluster configuration from the active command switch, including members that were added while it was
down. The active command switch sends a copy of the cluster configuration to the cluster standby group.

IP Addresses

You must assign IP information to a command switch. You can access the cluster through the
comman d-sw it ch IP a dd ress. I f yo u configu re a c luste r sta ndby gro up, you mu st u se the sta ndby-g rou p
virtual IP address to manage the cluster from the active command switch. Using the virtual IP address
ensures that you retain connectivity to the cluster if the active command switch fails and that a standby
command switch becomes the active command switch.
If the act ive command switch fails and the standby command switch take s over, you must either use th e
standby-group virtual IP address or the IP address a vailable on the new acti ve command switch to access
the cluster.
You can assig n an IP address to a clust er-capable swit ch, but it is not necessary. A member switch is
managed and communi cates with other mem ber switch es through the co mmand-swit ch IP address. If the
member switch leaves the cluster and it does not have its own IP address, you then must assign IP
information to it to manage it as a standalone switch.
Note Chang in g th e comm an d s witc h IP add ress e nds your CM S sessi on on t he sw itc h. Restar t yo ur CM S
session by entering the n ew IP address in the b rowser Location field (Netscape Communicator) or
Address field (Int er net Expl or er), a s d escri bed i n th e rel ease n otes.
For more informa tio n about IP addre sses, see Chapter 4, “Assigning the Switch IP Address and Default
Gateway.”