Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 195)

Multi-Service IronWare Switching Configuration Guide 165
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VLANs
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network constitute a single Layer 2 broadcast domain. Once you create a port-based VLAN and
assign an interface to that VLAN, that interface is automatically removed from the default VLAN if
the interface is assigned to the VLAN as an untagged interface. If the interface is assigned as a
tagged interface, then the interface is a member of both the default VLAN, and the VLAN to which it
is assigned.
Tagged, untagged, and dual mode ports
Interfaces assigned to port-based VLANs can be defined as untagged, tagged, and dual-mode
ports. An untagged port is a member of only one VLAN, while a tagged port can be a member of
more than one VLAN. Thus a tagged port can be a member of more than one broadcast domain.
Dual-mode ports are configured by adding one or more tagged VLANs and one untagged VLAN to a
port.
Tagged ports allow the Brocade device to add a four-byte 802.1q tag to the packet. 802.1q tagging
is an IEEE standard that allows a networking device to add information to Layer 2 packets. This
information identifies the VLAN membership of the packet, as well as the VLAN ID of the VLAN from
which the packet is sent. Furthermore, the default tag value of the 802.1q tag is 8100
(hexadecimal). This value comes from the IEEE 802.1q specification. You can change this tag value
on a per-port or on a global basis on a Brocade device if needed to be compatible with other
vendors’ equipment.
NOTE
On Brocade NetIron CES devices, you can change the tag value on the global basis for each VLAN
component (B-VLAN, C-VLAN, or S-VLAN).
Figure 8 shows the format of packets with and without the 802.1q tag.
FIGURE 8 Packet containing Brocade’s 802.1QVLAN tag