This con?¬?guration creates the most effective way to manage a
multiservice network.
VLAN Operation
A Cisco Catalyst switch operates in a network similar to a traditional bridge. Each VLAN
that you con?¬?gure on the switch implements address learning, forwarding and ?¬?ltering
decisions, and loop avoidance mechanisms as if the VLAN were a separate physical bridge.
The Cisco Catalyst switch implements VLANs by restricting traf?¬?c forwarding to
destination ports that are in the same VLAN as the originating ports. So when a frame
arrives on a switch port, the switch must retransmit the frame to only the ports that belong
to the same VLAN. In essence, a VLAN that is operating on a switch limits transmission of
unicast, multicast, and broadcast traf?¬?c. Traf?¬?c originating from a particular VLAN ?¬‚oods
to only the other ports in that VLAN.
A port normally carries only the traf?¬?c for the single VLAN to which it belongs. For a
VLAN to span across multiple switches, a trunk is required to connect two switches. A
trunk can carry traf?¬?c for multiple VLANs. Figure 2-6 shows a trunk carrying multiple
VLANs between two switches.
Figure 2-6 VLAN Trunk
IP IP
Trunk
Data VLAN
Data VLAN
Voice VLAN
24 Chapter 2: Medium-Sized Switched Network Construction
You con?¬?gure ports that belong to a VLAN with a membership mode that determines to
which VLAN they belong.
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