Cisco Systems 3750E manual 16-2, Private-VLAN Domain

Chapter 16 Configuring Private VLANs

Understanding Private VLANs

Figure 16-1 Private-VLAN Domain

	Primary
Private	VLAN
VLAN
domain
Subdomain	Subdomain

Secondary	Secondary
community VLAN	isolated VLAN

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There are two types of secondary VLANs:

•Isolated VLANs—Ports within an isolated VLAN cannot communicate with each other at the Layer 2 level.

•Community VLANs—Ports within a community VLAN can communicate with each other but cannot communicate with ports in other communities at the Layer 2 level.

Private VLANs provide Layer 2 isolation between ports within the same private VLAN. Private-VLAN ports are access ports that are one of these types:

•Promiscuous—A promiscuous port belongs to the primary VLAN and can communicate with all interfaces, including the community and isolated host ports that belong to the secondary VLANs associated with the primary VLAN.

•Isolated—An isolated port is a host port that belongs to an isolated secondary VLAN. It has complete Layer 2 separation from other ports within the same private VLAN, except for the promiscuous ports. Private VLANs block all traffic to isolated ports except traffic from promiscuous ports. Traffic received from an isolated port is forwarded only to promiscuous ports.

•Community—A community port is a host port that belongs to a community secondary VLAN. Community ports communicate with other ports in the same community VLAN and with promiscuous ports. These interfaces are isolated at Layer 2 from all other interfaces in other communities and from isolated ports within their private VLAN.

Note Trunk ports carry traffic from regular VLANs and also from primary, isolated, and community VLANs.

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

16-2 OL-9775-02