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Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide
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Chapter 15 Configuring Private VLANs
Configuring Private VLANs
Private-VLAN Configuration Guidelines
Guidelines for configuring private VLANs fall into these categories:
•
Secondary and Primary VLAN Configuration, page 15-7
•
Private-VLAN Port Configuration, page 15-8
•
Limitations with Other Features, page 15-9
Secondary and Primary VLAN Configuration
Follow these guidelines when configuring private VLANs:
•
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
Chapter 13, “Configuring VTP.”
•
You must use VLAN configuration (config-vlan) mode to configure private VLANs. You cannot
configure private VLANs in VLAN database configuration mode. For more information about
VLAN configuration, see
“VLAN Configuration Mode Options” section on page 12-7
.
•
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 does not propagate private-VLAN configuration. You must configure private VLANs on each
device where you want private-VLAN ports.
•
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.
•
We recommend that you prune the private VLANs from the trunks on devices that carry no traffic
in the private VLANs.
•
You can apply different quality of service (QoS) configurations to primary, isolated, and community
VLANs.
•
When you configure private VLANs, sticky Address Resolution Protocol (ARP) is enabled by
default, and ARP entries learned on Layer 3 private VLAN interfaces are sticky ARP entries. For
security reasons, private VLAN port sticky ARP entries do not age out.
Note
We recommend that you display and verify private-VLAN interface ARP entries.