Operation Manual – VLANH3C S5600 Series Ethernet Switches Chapter 1 VLAN Overview1-3Figure 1-2 Encapsulation format of traditional Ethernet framesIEEE 802.1Q inserts a four-byte VLAN tag after the DA&SA field, as shown in Figure1-3.Figure 1-3 Format of VLAN tagA VLAN tag comprises four fields: tag protocol identifier (TPID), priority, canonicalformat indicator (CFI), and VLAN ID.z The 16-bit TPID field with a value of 0x8100 indicates that the frame is VLANtagged. On the H3C series Ethernet switches, the default TPID is 0x8100.z The 3-bit priority field indicates the 802.1p priority of the frame. Refer to the“QoS-QoS profile” part of this manual for details.z The 1-bit CFI field specifies whether the MAC addresses are encapsulated in thecanonical format for the receiving device to correctly interpret the MAC addresses.Value 0 indicates that the MAC addresses are encapsulated in canonical format;value 1 indicates that the MAC addresses are encapsulated in non-canonicalformat. The field is set to 0 by default.z The 12-bit VLAN ID field identifies the VLAN the frame belongs to. The VLAN IDrange is 0 to 4095. As 0 and 4095 are reserved by the protocol, a VLAN ID actuallyranges from 1 to 4094.Note:The Ethernet II encapsulation format is used here. Besides the Ethernet IIencapsulation format, other encapsulation formats such as 802.2 LLC and 802.2 SNAPare also supported by Ethernet. The VLAN tag fields are also added to framesencapsulated in these formats for VLAN identification. Refer to section EncapsulationFormat of Ethernet Data for 802.2/802.3 encapsulation format.VLAN ID identifies the VLAN to which a packet belongs. When a switch receives apacket carrying no VLAN tag, the switch encapsulates a VLAN tag with the defaultVLAN ID of the inbound port for the packet, and sends the packet to the default VLAN ofthe inbound port for transmission. For the details about setting the default VLAN of aport, refer to Configuring the Default VLAN ID for a Port.
