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Egress rules – determines if the packet must be sent tagged
or untagged.
Figure 2-5. IEEE 802.1Q Packet Forwarding
802.1Q VLAN Tags
The figure below shows the 802.1Q VLAN tag. There are
four additional octets inserted after the source MAC address.
Their presence is indicated by a value of 0x8100 in the
EtherType field. When a packet's EtherType field is equal to
0x8100, the packet carries the IEEE 802.1Q/802.1p tag.
The tag is contained in the following two octets and consists
of 3 bits or user priority, 1 bit of Canonical Format Identifier
(CFI – used for encapsulating Token Ring packets so they
can be carried across Ethernet backbones) and 12 bits of
VLAN ID (VID). The 3 bits of user priority are used by
802.1p. The VID is the VLAN identifier and is used by the
130 VH-2402-L3 Management Guide
9033691-01
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