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Tag protocol identifier (TPID):
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16-bit is field set to 0x8100 to identify the packet as an 802.1Q packet.
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Priority code point (PCP):
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3-bit field indicates a class of service (CoS) as part of Layer 2 quality of service (QoS) between switches.
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Drop elgible indicator (DEI):
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This 1-bit field indicates whether the packet can be dropped when there is bandwidth contention.
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VLAN identifier (VLAN ID):
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This 12-bit field specifies the VLAN associated with a network packet.
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Centralized Forwarding
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⇨ When a route processor (RP) engine is equipped with a forwarding engine
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Distributed Forwarding
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⇨ Forwarding engines are equipped in the line cards
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⇨ When a packet is received on the ingress line card, it is transmitted to the local forwarding engine. The forwarding engine performs a packet lookup, and if it determines that the outbound interface is local, it forwards the packet out a local interface. If the outbound interface is located on a different line card, the packet is sent across the switch fabric, also known as the backplane, directly to the egress line card, bypassing the RP.
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VLAN 0
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Used for 802.1P Traffic Cannot be modified/deleted
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VLAN 1
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Default VLAN Cannot be modified/deleted
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VLAN 1002 to 1005
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Reserve Range Can be modified/deleted
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VLAN 2 to 1001
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Normal Range Can be modified/deleted
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VLAN 1006 to 4094
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Extended Range Can be modified/deleted
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