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Catalyst 3750 SwitchSoftware Configuration Guide
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Chapter16 Configuring Private VLANs
Configuring Private VLANs
Step5 If inter-VLAN routing will be used, configure the primary SVI, and map secondary VLANs to the
primary. See the “Mapping Secondary VLANs to a Primary VLAN Layer 3 VLAN Interface” section on
page 16-14.
Step6 Verify private-VLAN configuration.
Default Private-VLAN Configuration
No private VLANs are configured.
Private-VLAN Configuration Guidelines
Guidelines for configuring private VLANs fall into these categories:
•Secondary and Primary VLAN Configuration, page16-7
•Private-VLAN Port Configuration, page16-9
•Limitations with Other Features, page16-9

Secondary and Primary VLAN Configuration

Follow these guidelines when configuring private VLANs:
•If the switch is running VTP version 1 or 2, you must set VTP to transparent mode. After you
configure a private VLAN, you should not change the VTP mode to client or server. For information
about VTP, see Chapter14, “Configuring VTP.” VTP version 3 supports private VLANs in all
modes.
•With VTP version 1 or 2, after you have configured private VLANs, use the copy running-config
startup config privileged EXEC command to save the VTP transparent mode configuration and
private-VLAN configuration in the switch startup configuration file. Otherwise, if the switch resets,
it defaults to VTP server mode, which does not support private VLANs. VTP version 3 does support
private VLANs.
•VTP version 1 and 2 do not propagate private-VLAN configuration. You must configure private
VLANs on each device where you want private-VLAN ports unless the devices are running VTP
version 3.
•You cannot configure VLAN 1 or VLANs 1002 to 1005 as primary or secondary VLANs. Extended
VLANs (VLAN IDs 1006 to 4094) can belong to private VLANs
•A primary VLAN can have one isolated VLAN and multiple community VLANs associated with it.
An isolated or community VLAN can have only one primary VLAN associated with it.
•Although a private VLAN contains more than one VLAN, only one Spanning Tree Protocol (STP)
instance runs for the entire private VLAN. When a secondary VLAN is associated with the primary
VLAN, the STP parameters of the primary VLAN are propagated to the secondary VLAN.
•You can enable DHCP snooping on private VLANs. When you enable DHCP snooping on the
primary VLAN, it is propagated to the secondary VLANs. If you configure DHCP on a secondary
VLAN, the configuration does not take effect if the primary VLAN is already configured.
•When you enable IP source guard on private-VLAN ports, you must enable DHCP snooping on the
primary VLAN.