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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 11 Configuring STP Configuring Spanning-Tree Features
Figure 11-3 Spanning Tr ee and Redun dan t Connectiv ity
You can al so create redundan t links betwe en switch es by using EtherCha nnel gro ups. For more
inform ati on, see Chapter 27, Configuri ng EtherC hannels .

Accelerated Aging to Retain Connectivity

The default for aging dy namic addr esses is 5 minu tes, the defaul t setting of th e mac-address-table
aging-time g lo bal configur ation c om mand. H owever, a spanni n g-tre e r eco nfigura tio n ca n cause m any
statio n lo ca tio ns to ch an ge . Because th es e s ta tio ns co u ld be un reachab le f o r 5 min utes or more dur ing a
reconfig u ra tio n, th e ad dr ess - ag ing tim e is ac celerat ed so th at sta tio n addr es ses ca n b e dr o pped f ro m the
address tab le and then relearn ed. The accelerate d aging is the same as the forw ard-delay param eter value
(spanning-tree vlan vlan-id forward-time seconds global configurat ion comm and) wh en the spanni ng
tree reco nfigures.
Because each VLAN is a separate spanning-tree instance, the switch accelerates aging on a per-VLAN
basis. A spanning-tree reconfiguration on one VLAN can cause the dynamic addresses learned on that
VLAN t o be su bj ect to a cce ler ate d agi n g. D yna mic add re sses on ot h er V LAN s can be un affecte d an d
remain subject to the aging interval entered for the switch.

Configuring Sp anni ng-Tree Features

These sec tions de scribe how to configure span ning -tree fe ature s:
Default STP Configurat ion, page 11- 10
STP Configuration Gui delines, page 11- 10
Disabling STP, page 11-12
Configuring t he R oot Swit ch, page 1 1-12
Configuring a Se cond ar y R oot Swit ch, page 1 1-1 4
Configuring the Port Priority, page 11-15
Configuring the Path Cost, page 11-16
Configuring the Switch Priority of a VLAN, page 11-18
Catalyst 2950 or 3550
switch
Workstations
Catalyst 2950 or 3550
switch
Catalyst 2950 or 3550
switch
Switch A
Switch B
Active link
Blocked link
Switch C
74620