User's Manual

502 CHAPTER 13: VLAN MANAGEMENT
networks grow and the amount and types of traffic increase, bridge
flooding may create unnecessary traffic problems that can clog the
LAN. VLANs increase the efficiency of your network because each
VLAN can be set up to contain only those devices that need to
communicate with each other. With VLANs, if a bridge port receives a
packet with a broadcast, multicast, or unknown destination address,
the switch only forwards the packet to other ports in the same VLAN
as the receiving port.
802.1Q VLANs
The IEEE 802.1Q standard for VLANs aims to:
■ Define an architecture to logically partition bridged LANs and provide
services to defined user groups, independent of physical location.
■ Allow interoperability between multi-vendor equipment.
The 802.1Q standard allows each port on your switch to be placed in:
■ Any VLAN defined on the switch.
■ Several VLANs at the same time using 802.1Q tagging. The standard
specifies a tag format that embeds VLAN membership information
within each packet in a 12-bit VLAN ID (VID). This allows traffic from
multiple VLANs to be carried across one physical link.
The standard requires that you define the following information about
each VLAN on your switch before the switch can use it to forward traffic:
■ VLAN Name — This is a descriptive name for the VLAN for example,
Marketing or Management.
■ 802.1Q VLAN ID — This is used to identify the VLAN if you use
802.1Q tagging across your network. It can have a value from 1 to
4094, however VID 1 is reserved for the default VLAN. See “
The
Default VLAN” on page 504.
Port-based VLANs
A port-based VLAN is a collection of ports across one or more switches
that are configured as members of the same VLAN. Devices attached to
ports within the VLAN collection are members of the VLAN. In general,
VLANs on 3Com switches are port-based VLANs and as a result VLAN
support in 3Com Network Director is aimed at port-based VLANs.