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Advanced Concepts
Virtual LANs (VLANs)
Advanced Concepts
Virtual LANs (VLANs)
The switch supports port-based virtual LANs (VLANs). A VLAN is a collection
of ports that belong to a single broadcast domain. (That is, all ports carrying
traffic for a particular subnet address would belong to the same VLAN.) This
allows workgroups to be defined on the basis of their logical function instead
of their physical location, and does not require recabling.
Port-based VLANs are typically used to enable broadcast traffic reduction and
increased security. By using port groupings, traffic is isolated to specific
domains. A group of network users assigned to a VLAN are a separate traffic
domain so that packets are forwarded only between ports that are designated
for the same VLAN. Cross-domain broadcast traffic is eliminated and band-
width is saved by not allowing packets to flood throughout the network.
For example, if ports 1 through 4 belong to VLAN_1 and ports 5 through 8
belong to VLAN_2, traffic from end-node stations on ports 2 through 4 is
restricted to only VLAN 1, while traffic from ports 5 through 7 is restricted to
only VLAN 2. For nodes on VLAN_1 to communicate with VLAN_2, their traffic
must go through an external router via ports 1 and 8.
Figure 7-8. Example of Routing Between VLANs via an External Router
External
Router
VLAN_2
VLAN_1
Port 1
Port 8
Port 2
Port 3
Port 4
Port 5
Port 6
Port 7
Switch with Two
VLANs Configured
SEDONA.BK : sed_7.fm5 Page 14 Thursday, February 27, 1997 10:11 AM