Example 2, VLANs Across Multiple Switches
12-24 VLAN Operation and Network Applications
5. The switch adds the source MAC address and VLAN for station R2 to its Source Address Table
in FDB ID 2, and checks the Source Address Table for the destination MAC address given in
the frame. The switch finds the MAC address and VLAN in this table, and recognizes that the
MAC address and VLAN match for R1 is located out Port 1.
6. The switch examines its VLAN configuration information and determines that the frame for Red
VLAN is allowed to be forwarded out Port 1 and that it must be sent in an untagged format.
7. The switch forwards the frame out Port 1. Any other unicast transmissions between stations R1
and R2 will be handled identically.
12.13 EXAMPLE 2, VLANs ACROSS MULTIPLE SWITCHES
This second example investigates the steps that must be taken to set up VLANs across multiple
802.1Q VLAN switches. This includes the configuration and operation of trunk ports (port set for
TAGGED frames only) between 802.1Q VLAN switches.
As shown in Figure 12-12, two companies, “Redco” and “Blue Industries,” share floors 2 and 4 in
a building where the network infrastructure is supplied by the building owner. The objective is to
completely isolate the network traffic of the two companies by limiting the user’s traffic through
the ports of two switches, thus maintaining security and shielding the network traffic from each
company. This example will show the use and configuration of a trunk connection and the creation
of VLANs across multiple switches.