Huawei Quidway S3900 Series Operation Manual page 107

Operation Manual -- VLAN
Quidway S3900 Series Ethernet Switches-Release 1510
I. Ethernet II and 802.3 encapsulation
In the link layer, there are two main packet encapsulation types: Ethernet II and 802.3,
whose encapsulation formats are described in the following figures.
Ethernet II packet:
DA&SA(12) DA&SA(12) DA&SA(12)
Figure 1-4 Ethernet II encapsulation format
802.3 standard packet:
DA&SA(12) DA&SA(12)
Figure 1-5 802.3 standard encapsulation format
In the two figures, DA and SA refer to the destination MAC address and source MAC
address of the packet respectively. The number in the bracket indicates the field length
in bits.
The maximum length of an Ethernet packet is 1500 bytes, that is, 5DC in hexadecimal,
so the length field in 802.3 encapsulation is in the range of 0x0000 to 0x05DC.
Whereas, the type field in Ethernet II encapsulation is in the range of 0x0600 to
0xFFFF.
The switch identifies whether a packet is an Ethernet II packet or an 802.3 packet
according to the ranges of the two fields.
II. Encapsulation formats of 802.3 packets
802.3 packets are encapsulated in the following three formats:
802.3 raw encapsulation: only the length field is encapsulated after the source and
destination address field, followed by the upper layer data. The type field is not
included.
DA&SA(12) DA&SA(12) DA&SA(12) DA&SA(12) DA&SA(12)
DA&SA(12) DA&SA(12)
Figure 1-6 802.3 raw encapsulation format
Only the IPX protocol supports 802.3 raw encapsulation format currently. This format is
identified by the two bytes whose value is 0xFFFF after the length field.
802.3 logical link control (LLC) encapsulation: the length field, the destination
service access point (DASP) field, the source service access point (SSAP) field
and the control field are encapsulated after the source and destination address
field.
Type(2) Type(2)
Length(2) Length(2) DSAP(1) SSAP(1) Control(1) DSAP(1) SSAP(1) Control(1)
Length(2) Length(2)
Length(2) Length(2)
Huawei Technologies Proprietary
1-4
Chapter 1 VLAN Overview
DATA DATA DATA
OUI(3) PID(2) OUI(3) PID(2) DATA DATA
DATA DATA DATA DATA DATA
DATA DATA