6-4 User Guide for the Avaya P580 and P882 Multiservice Switches, v6.1
Chapter 6

IEEE 802.1Q VLAN

Tagging The Avay a Multiservi ce switch is comp liant with the IEEE 80 2.1Q standar d
for VLANs and defines a Tag Header. Two Tag formats are defined as an
Ethernet Encoded (4 bytes) for 802.3 and Ethernet V2 and SNAP (Service
Network Access Point) for Token Ri ng an d Fibe r Dis tribu ted Da ta I nterf ace
(FDDI).
The Ethernet version of the Tag Header consists of 4 bytes, two bytes for
Tag Protocol ID and two bytes for Tag Control. The Tag Protocol ID bytes
contain an Ethernet Type value of 81-00 which identifies the frame as a
tagged frame. The Tag Control specifies tag formats that are used to embed
explicit VLAN membership inform a tion within each frame in a 12-bit V ID
that provides 4094 possible VLAN ID’s. IEEE 802.1Q defines the bridging
rules for VLANs (ingress and egress rules which are described in detail i n
“VLAN Operation” later in this chapter).
VLAN Operation VLAN operation is based on three sets of rules:
■Ingress Rules
■Forwarding Rules
■Egress Rules
Ingress Rules
Every frame received by the switch is classified to one VLAN. There are
two ways in which frames are classified to VLANs:
■Untagged frames are classified to the VLAN associated with the
port on which the frame is received (P ort-based VLANs).
■Tagged frames are classified to the VLAN identified by the VLAN
tag in the tag header of the frame.
*Note: The switch supports a feature called Automatic VLAN
Creation for tagged frames. For more information, see
“VLAN Considerations” for more information.