Cisco Systems DOC-7814982 VLAN Configuration Mode Options

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Catalyst 2950 Desktop Switch Software Configuration Guide

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Chapter 14 Co n figuring VLANs

Configur ing Normal-R ange VLANs

•The switch supports 64 spanning-tree instances. If a switch has more activ e VLANs than supported

spannin g-tr ee i nsta nce s, spanni ng tree c an b e enab le d on 64 V LANs an d is di sabl ed on the

remaining VLANs. If you have already used all available spanning-tree instances on a switch,

adding another VLAN anywhere in the VTP domain creates a VLAN on that switch that is not

running spanni ng -tre e. I f you h ave the defau lt al lowed list on the tru nk p orts o f tha t sw itch (w hic h

is to a llow all VLA Ns ), th e new VLAN is ca rrie d o n all t ru nk po rts. Dep end ing o n the topo l ogy of

the network, this could create a loop in the new VLAN that would not be broken, particularly if there

are several adjacent switches that all have run out of spanning-tree instances. You can prevent this

possibility by setting allowed lists on the trunk ports of switches that have used up their allocation

of spanning-tree instances.

If the number of VLANs on the switch exceeds the number of supported spanning tree instances, we

recommend that you configure the IEEE 802.1S Multiple STP (MSTP) on your switch to map

multiple VLANs to a single STP instance. For more information about MSTP, see Chapter 12,

“Configuring RST P and MSTP.”

VLAN Configuration Mode Options

You can configur e nor ma l-ra nge V L ANs (with VLA N ID s 1 to 10 05) by using t hese two c onfiguration

modes:

•VLAN Configur ation in co nfig-vlan Mode , page 14-6

You acce ss config-v lan mode by enter ing the vlan vlan-id global configur ation comm and.

•VLAN Co nfigurat ion in VLA N Co nfigurat ion M ode, page 1 4-6

You acce ss VLAN configuratio n mode by enteri ng the vlan database privileged EXEC command.

To acces s config -vlan mode , enter the vlan global configuration command with a VLAN ID. Enter a new

VLAN ID to cr eate a VLAN or with an e xist ing VLAN ID to modif y the V LAN. You can u se the defa ult

VLAN configuration (Table 14-2) or enter multiple commands to configure the VLAN. For more

inform ation a bout co mmands available i n this mode , refer t o the vlan globa l co nfigurat ion com mand

descri ption in th e command referen ce for thi s releas e. When you have finished the con figuration, yo u

must exit config-vla n mode for t he configuration to take effect. To displa y the VLAN co nfiguration,

enter the show vlan privileged EXEC command.

You must use this config-v lan mode whe n creat ing extended- rang e VLANs (VL AN IDs gr eater tha n

1005). Se e the “Co nfiguring E xtende d-Ra nge V L ANs” sect ion on page 14-12.

To acc ess VL AN co nfigurati on mode , en ter th e vla n database privileged EXEC command. Then enter

the vlan command with a new VLAN ID to create a VLAN or with an existing VLAN ID to modify the

VLAN. Yo u ca n use the d efault VLAN con figurat ion (Table 14-2) or enter multiple commands to

configure the VLAN. For more information about keywords available in this mode, refer to the vlan

VLAN configuration command description in the command reference for this release. When you have

finished the co nfiguration, you mu st enter apply or exit for th e configurat ion to take effect. When you

enter the exit command, it applies all commands and updates the VLAN database. VTP messages are

sent to othe r switc hes in the VT P do mai n, and the pr ivileged EX EC mode p rom pt ap pea rs .