Configuring Modular QoS Service Packet Classification and Marking on Cisco ASR 9000 Series Routers
Information About Configuring Modular QoS Packet Classification and Marking on Cisco ASR 9000 Series Routers
QC-13
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
OL-23108-02
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.
Bundle Traffic Policies
When a policy is bound to a bundle, the same policy is programmed on every bundle member (port). For
example, if there is a policer or shaper rate, the same rate is configured on every port. Traffic is scheduled
to bundle members based on the load balancing algorithm.
A policy can be bound to:
• Bundles
• Bundle Layer 3 subinterfaces
• Bundle Layer 2 subinterfaces (Layer 2 transport)
Both ingress and egress traffic is supported. Percentage-based policies and absolute rate-based policies
are supported. However, for ease of use, it is recommended to use percentage-based policies.
Shared Policy Instance
After the traffic class and traffic policy have been created, Shared Policy Instance (SPI) can optionally
be used to allow allocation of a single set of QoS resources and share them across a group of
subinterfaces, multiple Ethernet flow points (EFPs), or bundle interfaces.
Using SPI, a single instance of qos policy can be shared across multiple subinterfaces, allowing for
aggregate shaping of the subinterfaces to one rate. All of the subinterfaces that share the instance of a
QoS policy must belong to the same physical interface. The number of subinterfaces sharing the QoS
policy instance can range from 2 to the maximum number of subinterfaces on the port.
For bundle interfaces, hardware resources are replicated per bundle member. All subinterfaces that use
a common shared policy instance and are configured on a Link Aggregation Control Protocol (LAG)
bundle must be load-balanced to the same member link.
When a policy is configured on a bundle EFP, one instance of the policy is configured on each of the
bundle member links. When using SPI across multiple bundle EFPs of the same bundle, one shared
instance of the policy is configured on each of the bundle member links. By default, the bundle load
balancing algorithm uses hashing to distribute the traffic (that needs to be sent out of the bundle EFPs)
among its bundle members. The traffic for single or multiple EFPs can get distributed among multiple
bundle members. If multiple EFPs have traffic that needs to be shaped or policed together usingSPI, the
bundle load balancing has to be configured to select the same bundle member (hash-select) for traffic to
all the EFPs that belong the same shared instance of the policy. This ensures that traffic going out on all
the EFPs with same shared instance of the policy use the same policer/shaper Instance.
This is normally used when the same subscriber has many EFPs, for example, one EFP for each service
type, and the provider requires shaping and queuing to be implemented together for all the subscriber
EFPs.
Configuration tasks for SPI are described in the “Configuring Shared Policy Instance” section on
page 26.
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