Intel 470F - NetStructure Switch User Manual page 19

C H A P T E R 2 Using the Intel® NetStructure™ 470T and 470F Switches
IEEE 802.1Q (tag)-based VLANs
The other type of VLAN supported by the 470 switches is based on the
IEEE 802.1Q specification. The specification provides a uniform way for
creating VLANs within a network and allows the creation of a VLAN that
can also span across the network. Until the release of the IEEE 802.1Q,
VLAN implementation had been vendor-specific, so it was not possible to
create a VLAN across devices from different vendors.
The 802.1Q VLAN works by using a tag added to the Ethernet frames. The
tag contains a VLAN Identifier (VID) that identifies the frame as belonging
to a specific VLAN. These tags allow switches that support the 802.1Q
specification to segregate traffic between devices and communicate a
device's VLAN association across switches.
There are multiple advantages to implementing 802.1Q VLANs. First, it
helps to contain broadcast and multicast traffic across the switch thus
improving performance. Second, ports can belong to more than one VLAN.
Third, VLANs can span multiple switches that support the 802.1Q
specification. Finally, it can provide security and improve performance by
logically isolating users and grouping them together.
A logical grouping may be mapped to a workgroup. For example, you can
create a VLAN that groups all the users from the engineering department. A
benefit of this logical grouping is that it improves performance by reducing
traffic that belongs to a different logical group (i.e. marketing), improves
security (engineering can't see marketing), and eases moves since the user
doesn't have to be physically located in the same group to participate in the
VLAN.
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470T Ch2.p65 13 3/30/00, 5:55 PM