Operation Manual – VLANH3C S3100 Series Ethernet Switches Chapter 1 VLAN Overview1-8values of specific fields. If a packet is matched, the switch will add a correspondingVLAN tag to it automatically. Thus, data of specific protocol is assigned automatically tothe corresponding VLAN for transmission.This feature is used for binding the ToS provided in the network to VLAN to facilitatemanagement and maintenance.1.3.2 Encapsulation Format of Ethernet DataThis section introduces the common encapsulation formats of Ethernet data for you tounderstand the procedure for the switch to identify the packet protocols.I. Ethernet II and 802.2/802.3 encapsulationThere are two encapsulation types of Ethernet packets: Ethernet II defined by RFC 894and 802.2/802.3 defined by RFC 1042. The two encapsulation formats are described inthe following figures.Ethernet II packet:Figure 1-4 Ethernet II encapsulation format802.2/802.3 packet:Figure 1-5 802.2/802.3 encapsulation formatIn the two figures, DA and SA refer to the destination MAC address and source MACaddress of the packet respectively. The number in the bracket indicates the field lengthin bytes.The maximum length of an Ethernet packet is 1500 bytes, that is, 0x05DC inhexadecimal, so the length field in 802.2/802.3 encapsulation is in the range of 0x0000to 0x05DC.Whereas, the type field in Ethernet II encapsulation is in the range of 0x0600 to0xFFFF.Packets with the value of the type or length field being in the range 0x05DD to 0x05FFare regarded as illegal packets and thus discarded directly.The switch identifies whether a packet is an Ethernet II packet or an 802.2/802.3 packetaccording to the ranges of the two fields.
