Private Vlan Configuration Restrictions And Guidelines; Configuring Private Vlans - Cisco 6500 Series Software Configuration Manual

Private VLAN Configuration Restrictions and Guidelines

Private VLAN ports are associated with a set of supporting VLANs that are used to create the private
VLAN structure. A private VLAN uses VLANs three ways:
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Note Isolated and community VLANs are both called secondary VLANs.
You can extend private VLANs across multiple devices by trunking the primary, isolated, and
community VLANs to other devices that support private VLANs.
In a switched environment, you can assign an individual private VLAN and associated IP subnet to each
individual or common group of end stations. The end stations only need to communicate with a default
gateway to gain access outside the private VLAN. With end stations in a private VLAN, you can do the
following:
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A promiscuous port can serve only one primary VLAN.
A promiscuous port can serve as many isolated or community VLANs as desired.
With a promiscuous port, you can connect a wide range of devices as "access points" to a private VLAN.
For example, you can connect a promiscuous port to the "server port" of LocalDirector to connect an
isolated VLAN or a number of community VLANs to the server so that LocalDirector can load balance
the servers present in the isolated or community VLANs, or you can use a promiscuous port to monitor
or back up all the private VLAN servers from an administration workstation.
Private VLAN Configuration Restrictions and Guidelines
Follow these restrictions and guidelines to configure private VLANs:
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Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
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Primary VLAN—Carries traffic from promiscuous ports to isolated, community, and other
promiscuous ports.
Isolated VLAN—Carries traffic from isolated ports to promiscuous ports.
Community VLAN—Carries traffic between community ports and to promiscuous ports. You can
configure multiple community VLANs in a private VLAN.
Designate selected ports connected to end stations (for example, interfaces connected to servers) as
isolated to prevent any communication at Layer 2. (For example, if the end stations were servers,
this configuration would prevent Layer 2 communication between the servers.)
Designate the interfaces to which the default gateway(s) and selected end stations (for example,
backup servers or LocalDirector) are attached as promiscuous to allow all end stations access.
Reduce VLAN and IP subnet consumption by preventing traffic between end stations even though
they are in the same VLAN and IP subnet.
Set VTP to transparent mode. After you configure a private VLAN, you cannot change the VTP
mode to client or server. See
You cannot include VLAN 1 or VLANs 1002 to 1005 in the private VLAN configuration.
Use only the private VLAN configuration commands to assign ports to primary, isolated, or
community VLANs. Layer 2 access ports assigned to the VLANs that you configure as primary,
isolated, or community VLANs are inactive while the VLAN is part of the private VLAN
configuration. Layer 2 trunk interfaces remain in the STP forwarding state.
Configure Layer 3 VLAN interfaces only for primary VLANs. Layer 3 VLAN interfaces for isolated
and community VLANs are inactive while the VLAN is configured as an isolated or community
VLAN.
Chapter 8, "Configuring VTP."
Chapter 10

Configuring Private VLANs

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