Справочник Пользователя для Enterasys Networks 2E253

In this example, the Sales and Finance workstations have been placed on two separate VLANs. In 
a plain Ethernet environment, the entire network is a broadcast domain, and the SmartSwitches 
follow the IEEE 802.1D bridging specification to send data between stations. A broadcast or 
multicast transmission from a Sales workstation in Building One would propagate to all the switch 
ports on SmartSwitch A, cross the high speed link to SmartSwitch B, and then propagated out all 
switch ports on SmartSwitch B. The SmartSwitches treat each port as being equivalent to any other 
port, and have no understanding of the departmental memberships of each workstation.

In a VLAN environment, each SmartSwitch understands that certain individual ports or frames are 
members of separate workgroups. In this environment, a broadcast or multicast data transmission 
from one of the Sales stations in Building One would reach SmartSwitch A, be sent to the ports 
connected to other local members of the Sales VLAN, cross the high speed link to SmartSwitch B, 
and then be sent to any other ports and workstations on SmartSwitch B that are members of the 
Sales VLAN.

There are a number of different strategies for creating Virtual Local Area Networks, each with 
their own approaches to defining a station’s membership in a particular VLAN. 

An 802.1Q VLAN switch determines the VLAN membership of a data frame by its Tag Header, 
described later in this chapter. If the frame received is not tagged, the switch classifies the frame 
into the VLAN that is assigned as the default VLAN of the switch. 

Some or all ports on the switch may be configured to operate as GARP VLAN Registration 
Protocol (GVRP) ports. If a frame received is tagged, the frame is forwarded to the GVRP ports 
that are configured to transmit frames associated with the frame VLAN ID and protocol. If the 
received frame is not tagged, the frame is examined and tagged as belonging to the default VLAN. 
Then the frame is forwarded to the GVRP ports that are configured to transmit frames associated 
with the default VLAN and the frame protocol. 

VLANs may also be created by a variety of addressing schemes, including the recognition of 
groups of MAC addresses or types of traffic. One of the best-known VLAN-like schemes is the use 
of IP Subnets to divide networks into smaller subnetworks.