Cisco Systems ME3400G2CSA Class Maps

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Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide
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Chapter30 Co nf iguring QoS
Understanding QoS
Figure30-3 QoS Classification Layers in Frames and Packets
These sections contain additional information about classification:
•“Class Maps” section on page 30-6
•“The match Command” section on page 30-7
•“Classification Based on Layer 2 CoS” section on page 30-7
•“Classification Based on IP Precedence” section on page30-8
•“Classification Based on IP DSCP” section on page30-8
•“Classification Comparisons” section on page 30-9
•“Classification Based on QoS ACLs” section on page 30-10
•“Classification Based on QoS Groups” section on page 30-10
Class Maps
As explained previously, you use an MQC class map to name a specific traffic flow (or class) and to
isolate it from all other traffic. A class map defines the criteria used to match against a specific traffic
flow to further classify it. If you have more than one type of traffic that y ou want to cla ssify, you can
create another class map and use a different name. When y ou en ter the c lass-map command with a
class-map name, the switch enters the class-map configuration m ode. In this mode, you define the match
criterion for the traffic by using the match class-map configuration command. After a packet is matched
against the class-map criteria, it is acted on by the associated action specified in a policy map.
141151
Layer 2 IEEE 802.1Q and IEEE 802.1P Frame
Preamble Start frame
delimiter DA
Len
SA Type TAG
4 Bytes PT Data FCS
Layer 3 IPv4 Packet
Version
length ToS
1 Byte ID Offset TTL Proto FCS IP-SA IP-DA
PRI
76 5 4 3 2 1 0
CFI VLAN ID
Data
3 bits used for CoS
(IEEE 802.1D user priority)
IP precedence
DSCP
Standard IPv4:
MSBs called IP precedence
Flow control
for DSCP