Default Traffic Class; Class-Based Unconditional Packet Marking Feature And Benefits - Cisco ASR 9000 Series Configuration Manual

Information About Configuring Modular QoS Packet Classification on Cisco ASR 9000 Series Routers
The traffic policy configuration task is described in the

Default Traffic Class

Unclassified traffic (traffic that does not meet the match criteria specified in the traffic classes) is treated
as belonging to the default traffic class.
If the user does not configure a default class, packets are still treated as members of the default class.
However, by default, the default class has no enabled features. Therefore, packets belonging to a default
class with no configured features have no QoS functionality. These packets are then placed into a first
in, first out (FIFO) queue and forwarded at a rate determined by the available underlying link bandwidth.
This FIFO queue is managed by a congestion avoidance technique called tail drop. For further
information about congestion avoidance techniques, such as tail drop, see the "Configuring Modular
QoS Congestion Avoidance on Cisco ASR 9000 Series Routers" module in this guide.

Class-based Unconditional Packet Marking Feature and Benefits

The Class-based, Unconditional Packet Marking feature provides users with a means for efficient packet
marking by which the users can differentiate packets based on the designated markings.
The Class-based, Unconditional Packet Marking feature allows users to perform the following tasks:
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Unconditional packet marking allows you to partition your network into multiple priority levels or
classes of service, as follows:
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The configuration task is described in the
section on page
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
QC-10
Configuring Modular Quality of Service Packet Classification on Cisco ASR 9000 Series Routers
D r a f t — C i s c o C o n f i d e n t i a l
Mark packets by setting the IP precedence bits or the IP differentiated services code point (DSCP)
in the IP ToS byte.
Mark Multiprotocol Label Switching (MPLS) packets by setting the EXP bits within the imposed or
topmost label.
Mark packets by setting the Layer 2 class-of-service (CoS) value. The priority value within an SRP
header can also be set.
Mark packets by setting the value of the qos-group argument.
Mark packets by setting the value of the discard-class argument.
Use QoS unconditional packet marking to set the IP precedence or IP DSCP values for packets
entering the network. Routers within your network can then use the newly marked IP precedence
values to determine how the traffic should be treated.
For example, weighted random early detection (WRED), a congestion avoidance technique, uses IP
precedence values to determine the probability that a packet is dropped. In addition, low-latency
queueing (LLQ) can then be configured to put all packets of that mark into the priority queue.
Use QoS unconditional packet marking to assign MPLS packets to a QoS group. The router uses the
QoS group to determine how to prioritize packets for transmission. To set the QoS group identifier
on MPLS packets, use the set qos-group command in policy map class configuration mode.
Use CoS unconditional packet marking to assign packets to set the priority value of IEEE 802.1p/
Inter-Switch Link (ISL) packets. The router uses the CoS value to determine how to prioritize
packets for transmission and can use this marking to perform Layer 2-to-Layer 3 mapping. To set
the Layer 2 CoS value of an outgoing packet, use the set cos command in policy map configuration
mode.
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"Creating a Traffic Policy" section on page
"Configuring Class-based Unconditional Packet Marking"
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