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If a packet is matched, the switch will add a corresponding VLAN tag to it automatically and thus the data of
specific protocol can be automatically assigned to the corresponding VLAN for transmission. The network
administrator can manage network clients based on their specific applications and services through protocol VLAN.
Encapsulation Format of Ethernet Data
At present there are two encapsulation formats of Ethernet data, Ethernet II encapsulation and 802.2/802.3
encapsulation, shown as follows:
Ethernet II
Ethernet II framing (also known as DIX Ethernet, named after DEC, Intel and Xerox, the major participants in its
design), defines the two-octet EtherType field in an Ethernet frame, preceded by destination and source MAC
addresses, that identifies an upper layer protocol encapsulating the frame data. Once Frame type on this device is
set to Ethernet II, Ether Type of this protocol VLAN will match 13-14th bytes of packets for VLAN mapping.
Destination MAC Address
Source MAC Address
Type
Data
CRC
6
6
2
46-1500
4
802.2/802.3
802.3, same as Ethernet II (above) except Type field is replaced by Length, and an 802.2 LLC header follows the
802.3 header. When Frame Type on this device is set to LLC, Ether Type of this protocol VLAN will match
16-18th bytes of the packet for VLAN mapping.
Ethernet SNAP
The biggest difference between Ethernet SNAP Frame and 802.3/802.2 Frame is the addition of 5-byte SNAP ID.
The previous 3 bytes, manufacturer ID, are the same as those of the source MAC address and sometimes can be set
to 0. The last 2 bytes are the same as Type Field of Ethernet II. When Frame Type on this device is set to SNAP,
Ether Type of this protocol will match 23-24th bytes of the packet for VLAN mapping and 16-21th bytes:
AA-AA-03-00-00-00.
The Procedure for the Switch to Process Protocol VLAN Packets
VLAN packets are processed in the following way:
1. When receiving an untagged packet, the switch matches the packet with the current Protocol VLAN. If the
packet is matched, the switch will add a corresponding Protocol VLAN tag to it. If no Protocol VLAN is matched,
the switch will add a tag to the packet according to the PVID of the received port and forward packets in the
corresponding VLAN. Thus, the packet is assigned automatically to the corresponding VLAN for transmission.
2. When receiving tagged packet, the switch will process it based on the 802.1Q VLAN. If the received port is the
member of the VLAN to which the tagged packet belongs, the packet will be forwarded normally. Otherwise, the
packet will be discarded.
Summary of Contents for G3224P
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