Allied Telesis AT-S63 - Manual (Page 284)

Chapter 14: Classifiers
284 Section II: Advanced Operations
Figure 84. 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 84, 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 any of the following Layer 2 protocols:
ˆ IP
ˆ ARP
ˆ RARP
ˆ Protocol Number
Observe the following guideline when using this variable:
ˆ When selecting a Layer3 or Layer 4 variable, this variable must be left
blank or set to IP.
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