Output Policy Maps; Classification - Cisco ME 3400 Software Configuration Manual

Chapter 33 Configuring QoS
Only input policies provide matching on access groups or VLAN IDs, and only output policies provide
matching on QoS groups. You can assign a QoS group number in an input policy and match it in the
output policy. The class class-default is used in a policy map for any traffic that does not explicitly
match any other class in the policy map. Input policy maps do not support queuing and scheduling
keywords, such as bandwidth, queue-limit, priority, and shape average.
An input policy map can have a maximum of 64 classes plus class-default. You can configure a
maximum of 64 classes in an input policy.

Output Policy Maps

Output policy map classification criteria include matching a CoS, a DSCP, an IP precedence, or a QoS
group value. Output policy maps can have any of these actions:
•
•
Output policy maps do not support matching of access groups. You can use QoS groups as an alternative
by matching the appropriate access group in the input policy map and setting a QoS group. In the output
policy map, you can then match the QoS group. See the
on page 33-10
Output policies do not support marking or policing (except in the case of priority with policing). There
is no egress packet marking on the switch (no set command in an output policy).
The class class-default is used in a policy map for any traffic that does not explicitly match any other
class in the policy map. There can be a maximum of four classes in the output policy map (including
class-default) because egress ports have a maximum of four queues.
An output policy map attached to an egress port can match only the packets that have already been
matched by an input policy map attached to the ingress port for the packets. You can attach an output
policy map to any or all ports on the switch. The switch supports configuration and attachment of a
unique output policy map for each port. However, these output policy maps can contain only three unique
configurations of queue limits. These three unique queue-limit configurations can be included in as many
output policy maps as there are ports on the switch. There are no limitations on the configurations of
bandwidth, priority, or shaping.
You can configure the output policy classification criteria for CPU-generated traffic by using the cpu
traffic qos [cos value | dscp value | precedence value | qos-group value] global configuration command.

Classification

Classification distinguishes one kind of traffic from another by examining the fields in the packet header.
When a packet is received, the switch examines the header and identifies all key packet fields. A packet
can be classified based on an ACL, on the DSCP, the CoS, or the IP precedence value in the packet, or
by the VLAN ID.
3 IP packet header, using six bits from the deprecated IP type of service (ToS) field to carry the
classification information.
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OL-9639-07
Queuing (queue-limit)
Scheduling (bandwidth, priority, and shape average)
for more information.
Figure 33-3 has examples of classification information carried in a Layer 2 or a Layer
On ports configured as Layer 2 IEEE 802.1Q trunks, all traffic is in 802.1Q frames except for traffic
in the native VLAN. Layer 2 802.1Q frame headers have a 2-byte Tag Control Information field that
carries the CoS value, called the User Priority bits, in the three most-significant bits, and the VLAN
ID value in the 12 least-significant bits. Other frame types cannot carry Layer 2 CoS values.
Layer 2 CoS values range from 0 to 7.
"Classification Based on QoS Groups" section
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Understanding QoS
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