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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
74 Switch Management and Operating Concepts
• Forwarding rules between ports – decides filter or
forward the packet
• Egress rules – determines if the packet must be sent
tagged or untagged.
Figure 5-6. 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