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220 CHAPTER 7: QOS/ACL OPERATION
Configuring Packet Filtering
Before initiating any of these QoS configuration tasks, you should first define the
corresponding ACL. Then you can achieve packet filtering just by activating the
right ACL.
Some of QoS terms are listed in the following table.
Configuring the Service Parameter Allocation Rule
QoS is based on service parameters, a set of parameters for a packet, including
802.1p priority (CoS priority), DSCP priority, local precedence and drop
precedence.
After receiving a packet, the switch allocates a set of service parameters to it
according to a specific rule. The switch first gets its local precedence and drop
precedence according to the packet 802.1p priority value, by searching in the CoS
-> Local-precedence mapping table and the CoS -> Drop-precedence mapping
table. Default values are available for the two mapping tables, but you can also
configure the mapping tables according to your needs. If the switch cannot
allocate local precedence for the packet, it uses the default local precedence of the
port for the packet. After obtaining packet local precedence, the switch then gets
drop precedence according to the CoS -> Drop-precedence mapping table (local
precedence value is used as CoS value in this process).
Configuring the Mapping Table Perform the following configurations in
system view.
Table 11 QoS Terms
Term Description
CoS Means the same as 802.1p priority. Both refer to the priority at packet
header, with the value ranging from 0 to 7.
Service parameters Switch allocates a set of parameters, which are used in achieving QoS
functions, upon receiving a packet. Four items are included: 802.1p
priority, DSCP priority, local precedence and drop precedence.
Drop-precedence One of the service parameters, ranging from 0 to 2. Drop precedence is
allocated when the switch receives the packet and may be when the
packet is processed. Allocating drop precedence to the packet is also
called coloring the packet: the packet with drop precedence 2 as red,
that with drop precedence 1 as yellow and that with drop precedence 0
as green. Drop precedence is referred to when switch needs to drop
packets when it is congested
Conform-level The result calculated by the user-defined CIR, CBS, EBS, PIR and actual
traffic when the switch runs traffic policing, in the range of 0 to 2. It is
used as a parameter in the traffic-limit command (here the value
depends on the calculated result). It is also involved in the DSCP +
Conform level —> Service parameter mapping table which is used in
re-allocating service parameters to a packet with the traffic-priority
command. Then Conform-Level must be 0.
Table 12 Configuring Mapping Tables
Operation Command
Configure the CoS -> Drop-precedence
mapping table
qos cos-drop-precedence-map
cos0-map-drop-prec cos1-map-drop-prec
cos2-map-drop-prec cos3-map-drop-prec
cos4-map-drop-prec cos5-map-drop-prec
cos6-map-drop-prec cos7-map-drop-prec