Brocade TurboIron 24X Series Configuration Guide - Manual (Page 401)

Brocade TurboIron 24X Series Configuration Guide 367
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VLAN overview
When you configure a port-based VLAN, one of the configuration items you provide is the ports that
are in the VLAN. When you configure the VLAN, the device automatically removes the ports that you
place in the VLAN from DEFAULT-VLAN. By removing the ports from the default VLAN, the device
ensures that each port resides in only one Layer 2 broadcast domain.
NOTE
Information for the default VLAN is available only after you define another VLAN.
Some network configurations may require that a port be able to reside in two or more Layer 2
broadcast domains (port-based VLANs). In this case, you can enable a port to reside in multiple
port-based VLANs by tagging the port. See the following section.
If your network requires that you use VLAN ID 1 for a user-configured VLAN, you can reassign the
default VLAN to another valid VLAN ID. Refer to
“Assigning a different VLAN ID to the default VLAN”
on page 376.
802.1Q tagging
802.1Q tagging is an IEEE standard that allows a networking device to add information to a Layer 2
packet in order to identify the VLAN membership of the packet. Devices tag a packet by adding a
four-byte tag to the packet. The tag contains the tag value, which identifies the data as a tag, and
also contains the VLAN ID of the VLAN from which the packet is sent.
• The default tag value is 8100 (hexadecimal). This value comes from the 802.1Q specification.
You can change this tag value on a global basis on devices if needed to be compatible with
other vendors’ equipment.
• The VLAN ID is determined by the VLAN on which the packet is being forwarded.
Figure 38 shows the format of packets with and without the 802.1Q tag. The tag format is
vendor-specific. To use the tag for VLANs configured across multiple devices, make sure all the
devices support the same tag format.