Operation Manual – VLANH3C S7500 Series Ethernet Switches Chapter 1 VLAN Overview1-3Type DataDA&SAFigure 1-2 Encapsulation format of traditional Ethernet framesIn Figure 1-2 DA refers to the destination MAC address, SA refers to the source MACaddress, and Type refers to the protocol type of the packet. IEEE 802.1Q protocoldefines that a 4-byte VLAN tag is encapsulated after the destination MAC address andsource MAC address to show the information about VLAN.TPIDDA&SA Priority CFI VL TypeAN IDVLAN TagFigure 1-3 Format of VLAN tagAs shown in Figure 1-3, a VLAN tag contains four fields, including TPID, priority, CFI,and VLAN ID.z TPID is a 16-bit field, indicating that this data frame is VLAN-tagged. By default, itis 0x8100 in H3C series Ethernet switches.z Priority is a 3-bit field, referring to 802.1p priority. Refer to “QoS” part for details.z CFI is a 1-bit field, indicating whether the MAC address is encapsulated in thestandard format in different transmission media. This field is not described in detailin this chapter.z VLAN ID is a 12-bit field, indicating the ID of the VLAN to which this packetbelongs. It is in the range of 0 to 4,095. Generally, 0 and 4,095 is not used, so theVLAN ID is in the range of 1 to 4,094.VLAN ID identifies the VLAN to which a packet belongs. When the switch receives anun-VLAN-tagged packet, it will encapsulate a VLAN tag with the default VLAN ID of theinbound port for the packet, and the packet will be assigned to the default VLAN of theinbound port for transmission. For the details about setting the default VLAN of a port,refer to the “Port Basic Configuration” part of the H3C S7500 Series Ethernet Switches– Operation Manual.1.2 Port-Based VLANPort-based VLAN technology introduces the simplest way to classify VLANs. You canisolate the hosts and divide them into different virtual workgroups through assigning theports on the device connecting to hosts to different VLANs.This way is easy to implement and manage and it is applicable to hosts with relativelyfixed positions.
