User Guide
51
4.3.3 Protocol VLAN
Overview
Protocol VLAN, another way to classify VLANs based on network protocol, can bind ToS provided in the
network to VLAN to realize the specific service. Through protocol VLAN, the switch can analyze the
received untagged packets on the port and match the packets with the user-defined protocol template
according to different encapsulation formats and the values of the special fields.
If a packet is matched, the switch will add a corresponding VLAN tag to it automatically and thus the data
of specific protocol can be automatically assigned to the corresponding VLAN for transmission. The
network administrator can manage network clients based on their specific applications and services
through protocol VLAN.
Encapsulation Format of Ethernet Data
At present there are two encapsulation formats of Ethernet data, Ethernet II encapsulation and
802.2/802.3 encapsulation, shown as follows:
Ethernet II
Ethernet II framing (also known as DIX Ethernet, named after DEC, Intel and Xerox, the major
participants in its design), defines the two-octet EtherType field in an Ethernet frame, preceded by
destination and source MAC addresses, which identifies an upper layer protocol encapsulating the frame
data. Once Frame type on this device is set to Ethernet II, Ether Type of this protocol VLAN will match
13-14th bytes of packets for VLAN mapping.
Destination
MAC
Address
Source
MAC
Address
Type
Data
CRC
6
6
2
46-1500
4
802.2/802.3
802.3, same as Ethernet II (above) except Type field is replaced by Length, and an 802.2 LLC header
follows the 802.3 header. When Frame Type on this device is set to LLC, Ether Type of this protocol
VLAN will match 16-18th bytes of the packet for VLAN mapping.
Ethernet SNAP
The biggest difference between Ethernet SNAP Frame and 802.3/802.2 Frame is the addition of 5-byte
SNAP ID. The previous 3 bytes, manufacturer ID, are the same as those of the source MAC address and
sometimes can be set to 0. The last 2 bytes are the same as Type Field of Ethernet II. When Frame Type
on this device is set to SNAP, Ether Type of this protocol will match 23-24th bytes of the packet for VLAN
mapping and 16-21th bytes: AA-AA-03-00-00-00.
The Procedure for the Switch to Process Protocol VLAN Packets
VLAN packets are processed in the following way:
1. When receiving an untagged packet, the switch matches the packet with the current Protocol VLAN. If
the packet is matched, the switch will add a corresponding Protocol VLAN tag to it. If no Protocol VLAN is
