Chapter 16 Configuring Private VLANs

Understanding Private VLANs

Private VLANs across Multiple Switches

As with regular VLANs, private VLANs can span multiple switches. A trunk port carries the primary VLAN and secondary VLANs to a neighboring switch. The trunk port treats the private VLAN as any other VLAN. A feature of private VLANs across multiple switches is that traffic from an isolated port in switch A does not reach an isolated port on Switch B. See Figure 16-2.

Figure 16-2 Private VLANs across Switches

Trunk ports

VLAN 100

VLAN 100

Switch B

Switch A

 

 

 

 

 

 

 

 

 

 

 

 

 

VLAN 201

VLAN 202

VLAN 201

VLAN 202

 

 

 

 

 

 

 

 

 

 

 

 

 

Carries VLAN 100, 201, and 202 traffic

VLAN 100 = Primary VLAN

VLAN 201 = Secondary isolated VLAN

VLAN 202 = Secondary community VLAN

116084

Because VTP does not support private VLANs, you must manually configure private VLANs on all switches in the Layer 2 network. If you do not configure the primary and secondary VLAN association in some switches in the network, the Layer 2 databases in these switches are not merged. This can result in unnecessary flooding of private-VLAN traffic on those switches.

Note When configuring private VLANs on the switch, always use the default Switch Database Management (SDM) template to balance system resources between unicast routes and Layer 2 entries. If another SDM template is configured, use the sdm prefer default global configuration command to set the default template. See Chapter 8, “Configuring SDM Templates.”

Private-VLAN Interaction with Other Features

Private VLANs have specific interaction with some other features, described in these sections:

Private VLANs and Unicast, Broadcast, and Multicast Traffic, page 16-5

Private VLANs and SVIs, page 16-5

Private VLANs and Switch Stacks, page 16-6

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

16-4

OL-9775-02

 

 

Page 406
Image 406
Cisco Systems 3750E manual Private VLANs across Multiple Switches, Private-VLAN Interaction with Other Features, 16-4