Allied Telesis AT-S63 - Manual (Page 114)

Chapter 10: Classifiers
114 Section II: Advanced Operations
Figure 2. User Priority and VLAN Fields within an Ethernet Frame
You can identify a traffic flow of tagged packets using the user priority
value. A classifier for such a traffic flow would instruct a port to watch for
tagged packets containing the specified user priority level.
The priority level criteria can contain only one value, and the value must
be from 0 (zero) to 7. Multiple classifiers are required if a port is to watch
for several different traffic flows of different priority levels.
VLAN ID (Layer 2)
A tagged Ethernet frame also contains within it a field of 12 bits that
specifies the ID number of the VLAN to which the frame belongs. The
field, illustrated in Figure 2, can be used to identify a traffic flow.
A classifier can contain only one VLAN ID. To create a port ACL or QoS
policy that applies to several different VLAN IDs, multiple classifiers are
required.
Protocol (Layer 2)
Traffic flows can be identified by the protocol specified in the Ethertype
field of the MAC header in an Ethernet II frame. Possible values are:
ˆ IP
ˆ ARP
ˆ RARP
ˆ Protocol Number
Preamble
Destination
Address
Source
Address
Type/
Length Frame Data CRC
64 bits 48 bits 48 bits
16
bits
368 to 12000 bits 32 bits
Tag Protocol Identifier
User
Priority CFI VLAN Identifier
16 bits 3 bits
1
bit
12 bits