Chapter 2. VLANs | 9
2
2. VLANs
Virtual LANs
This chapter provides the following examples:
• Create Two VLANs on page 10
• Assign Ports to VLAN2 on page 12
• Assign Ports to VLAN3 on page 13
• Assign VLAN3 as the Default VLAN for Port 1/0/2 on page 15
• Create a MAC-Based VLAN on page 16
• Create a Protocol-Based VLAN on page 19
• Virtual VLANs: Create an IP Subnet–Based VLAN on page 21
• Voice VLANs on page 24
Adding virtual LAN (VLAN) support to a Layer 2 switch offers some of the benefits of both
bridging and routing. Like a bridge, a VLAN switch forwards traffic based on the Layer 2 header,
which is fast. Like a router, it partitions the network into logical segments, which provides better
administration, security, and management of multicast traffic.
A VLAN is a set of end stations and the switch ports that connect them. You can have different
reasons for the logical division, such as department or project membership. The only physical
requirement is that the end station and the port to which it is connected both belong to the same
VLAN.
Each VLAN in a network has an associated VLAN ID, which appears in the IEEE 802.1Q tag in
the Layer 2 header of packets transmitted on a VLAN. An end station might omit the tag, or the
VLAN portion of the tag, in which case the first switch port to receive the packet can either reject
it or insert a tag using its default VLAN ID. A given port can handle traffic for more than one
VLAN, but it can support only one default VLAN ID.
The Private Edge VLAN feature lets you set protection between ports located on the switch. This
means that a protected port cannot forward traffic to another protected port on the same switch.
The feature does not provide protection between ports located on different switches.
The diagram in this section shows a switch with four ports configured to handle the traffic for two
VLANs. Port 1/0/2 handles traffic for both VLANs, while port 1/0/1 is a member of VLAN 2 only,
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