Huawei Quidway S3900 Series Operation Manual page 108

Operation Manual -- VLAN
Quidway S3900 Series Ethernet Switches-Release 1510
DA&SA(12) DA&SA(12)
Figure 1-7 802.3 LLC encapsulation format
The DSAP field and the SSAP field in the LLC part are used to identify the upper layer
protocol. For example, the two fields are both 0xE0, meaning that the upper layer
protocol is IPX protocol.
802.3 sub-network access protocol (SNAP) encapsulation: the length field, the
DSAP filed, the SSAP field, the control field, the OUI field and the PID field are
encapsulated according to 802.3 standard packets.
DA&SA(12) DA&SA(12)
Figure 1-8 802.3 SNAP encapsulation format
In 802.3 SNAP encapsulation format, the values of the DSAP field and the SSAP field
are always AA, and the value of the control field is always 3.
The switch differentiates between 802.3 LLC encapsulation and 802.3 SNAP
encapsulation according to the values of the DSAP field and the SSAP field.
Note:
When the OUI is 00-00-00 in 802.3 SNAP encapsulation, the PID field has the same
meaning as the type field in Ethernet II encapsulation, which both refer to globally
unique protocol number. Such encapsulation is also known as SNAP RFC1042
encapsulation, which is standard SNAP encapsulation. The SNAP encapsulation
mentioned in this chapter refers to SNAP RFC 1042 encapsulation.
Length(2) Length(2) DSAP(1) SSAP(1) Control(1) DSAP(1) SSAP(1) Control(1)
Length(2) Length(2) DSAP(1) SSAP(1) Control(1) DSAP(1) SSAP(1) Control(1)
Huawei Technologies Proprietary
1-5
Chapter 1 VLAN Overview
DATA DATA
OUI(3) PID(2) OUI(3) PID(2) DATA DATA