Handbook

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VLANs
Introduction
This chapter describes network design and topology considerations for using Virtual Local Area Networks
(VLANs). VLANs are commonly used to split up groups of network users into manageable broadcast
domains, to create logical segmentation of workgroups, and to enforce security policies among logical
segments.
The following topics are discussed in this chapter:
VLANs and Port VLAN ID Numbers
VLAN Tagging
VLANs and IP Interfaces
VLAN Topologies and Design Considerations
NOTE: Basic VLANs can be configured during initial switch configuration.
More comprehensive VLAN configuration can be done from the command line interface. See the
Command Reference Guide
Overview
Setting up VLANs is a way to segment networks to increase network flexibility without changing the
physical network topology. With network segmentation, each switch port connects to a segment that is a
single broadcast domain. When a switch port is configured to be a member of a VLAN, it is added to a
group of ports (workgroup) that belongs to one broadcast domain.
Ports are grouped into broadcast domains by assigning them to the same VLAN. Multicast, broadcast,
and unknown unicast frames are flooded only to ports in the same VLAN.
VLANs and port VLAN ID numbers
VLAN numbers
This switch supports up to 1,000 VLANs per switch. Even though the maximum number of VLANs supported
at any given time is 1,000, each can be identified with any number between 1 and 4095. VLAN 1 is the
default VLAN, and all ports (except port 17) are assigned to it. VLAN 4095 is reserved for switch
management, and it cannot be configured.
Viewing VLANs
The VLAN information menu (/info/l2/vlan) displays all configured VLANs and all member ports that have
an active link state, for example:
>> Layer 2# vlan
VLAN Name Status Ports
---- -------------------------------- ------ ----------------------
1 Default VLAN ena 1 4-18 20-21
2 VLAN 2 ena 2 3
4095 VLAN 4095 ena 17
PVID numbers
Each port in the switch has a configurable default VLAN number, known as its PVID. This places all ports
on the same VLAN initially, although each port PVID is configurable to any VLAN number between 1 and
4094.
The default configuration settings for switches have all ports (except port 17) set as untagged members of
VLAN 1 with all ports configured as PVID = 1. In the default configuration example shown in the following
figure, all incoming packets are assigned to VLAN 1 by the default port VLAN identifier (PVID =1).