User`s guide

VLAN Switch Operation
DIGITAL MultiSwitch 700 Port Based VLAN User’s Guide 2-3
2.3.4 Customizing the Port’s Egress List
When the VLAN Forwarding List is fully configured, the Egress List for
each port may be customized if needed. The entries in the Egress List
allow traffic classified into specific VLANs to be transmitted out the port.
2.3.5 Setting the Operational Mode
Once the VLANs are in place, the operation of the switch is dependent
upon the method of operation specified by the Administrator. All port
based VLAN switches can be set to one of two operational modes: Open
and Secure. The mode configuration of a switch determines how the
switch handles the frames that it receives. The differences between the
two modes are discussed in Section 2.4, VLAN Switch Operation, below.
2.4 VLAN SWITCH OPERATION
Prestandard IEEE 802.1Q VLAN switches act on the classification of
frames into VLANs. Sometimes, VLAN classification is based on tags in
the headers of data frames. These VLAN tags are added to data frames by
the switch as the frames are transmitted out certain interfaces, and are
later used to make forwarding decisions by the switch and other VLAN
aware switches. In the absence of a VLAN Tag header, the classification
of a frame into a particular VLAN depends upon the configuration of the
switch port that received the frame.
The operation of a port based VLAN switch is best understood from a
point of view of the switch itself. To illustrate this concept, the examples
that follow view the switch operations from inside the switch.
Figure 2-1 depicts the inside of a switch with four interfaces, numbered
one through four. The switch knows that interfaces 1 and 2 belong to
VLAN A. Interface 3 belongs to VLAN B. Interface 4 is a trunk port
belonging to all VLANs. At intervals, frames come in to the switch
through these interfaces and are examined.