Vlans - Cisco Catalyst 4500 Series Configuration Manual

Layer 2 Software Features

VLANs

A VLAN configures switches and routers according to logical, rather than physical, topologies. Using
VLANs, you can combine any collection of LAN segments within an internetwork into an autonomous
user group, such that the segments appear as a single LAN in the network. VLANs logically segment the
network into different broadcast domains so that packets are switched only between ports within the
VLAN. Typically, a VLAN corresponds to a particular subnet, although not necessarily.
For more information about VLANs, VTP, and Dynamic VLAN Membership, see
"Configuring VLANs, VTP, and VMPS."
The following VLAN-related features also are supported:
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Virtual Switch System Client
Catalyst 4500 series switches support enhanced PAgP. If a Catalyst 4500 series switch is connected to a
Catalyst 6500 series Virtual Switch System (VSS) by using a PAgP EtherChannel, the Catalyst 4500
series switch will automatically serve as a VSS client, using enhanced PAgP on this EtherChannel for
dual-active detection. This VSS client feature has no impact on the performance of Catalyst 4500 series
switches and does not require any user configuration.
For information on VSS, see
Y.1731 (AIS and RDI)
Y.1731 ETH-AIS (Ethernet Alarm Indication Signal function) and ETH-RDI (Ethernet Remote Defect
Indication function) provides fault and performance management for service providers in large
networks.
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
1-10
VLAN Trunking Protocol (VTP)—VTP maintains VLAN naming consistency and connectivity
between all devices in the VTP management domain. You can have redundancy in a domain by using
multiple VTP servers, through which you can maintain and modify the global VLAN information.
Only a few VTP servers are required in a large network.
Private VLANs—Private VLANs are sets of ports that have the features of normal VLANs and also
provide some Layer 2 isolation from other ports on the switch.
For information about private VLANs, see
Private VLAN Trunk Ports—Private VLAN trunk ports allow a secondary port on a private VLAN
to carry multiple secondary VLANs.
Private VLAN Promiscuous Trunk Ports—Private VLAN promiscuous trunk extends the
promiscuous port to a 802.1Q trunk port, carrying multiple primary VLANs (hence multiple
subnets). Private VLAN promiscuous trunk is typically used to offer different services or content on
different primary VLANs to isolated subscribers. Secondary VLANs can not be carried over the
private VLAN promiscuous trunk.
Dynamic VLAN Membership—Dynamic VLAN Membership allows you to assign switch ports to
VLANs dynamically, based on the source Media Access Control (MAC) address of the device
connected to the port. When you move a host from a port on one switch in the network to a port on
another switch in the network, that switch dynamically assigns the new port to the proper VLAN for
that host. With the VMPS Client feature, you can convert a dynamic access port to a VMPS client.
VMPS clients can use VQP queries to communicate with the VMPS server to obtain a VLAN
assignment for the port based on the MAC address of the host attached to that port.
Chapter 24, "Configuring EtherChannel and Link State Tracking."
Chapter 42, "Configuring Private VLANs."
Chapter 1 Product Overview
Chapter 15,
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