- play_arrow Overview
- play_arrow Understanding How Class of Service Manages Congestion and Defines Traffic Forwarding Behavior
- Understanding How Class of Service Manages Congestion and Controls Service Levels in the Network
- How CoS Applies to Packet Flow Across a Network
- The Junos OS CoS Components Used to Manage Congestion and Control Service Levels
- Mapping CoS Component Inputs to Outputs
- Default Junos OS CoS Settings
- Packet Flow Through the Junos OS CoS Process Overview
- Configuring Basic Packet Flow Through the Junos OS CoS Process
- Example: Classifying All Traffic from a Remote Device by Configuring Fixed Interface-Based Classification
- Interface Types That Do Not Support Junos OS CoS
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- play_arrow Configuring Platform-Specific Functionality
- play_arrow Configuring Class of Service on ACX Series Universal Metro Routers
- CoS on ACX Series Routers Features Overview
- Understanding CoS CLI Configuration Statements on ACX Series Routers
- DSCP Propagation and Default CoS on ACX Series Routers
- Configuring CoS on ACX Series Routers
- Classifiers and Rewrite Rules at the Global, Physical, and Logical Interface Levels Overview
- Configuring Classifiers and Rewrite Rules at the Global and Physical Interface Levels
- Applying DSCP and DSCP IPv6 Classifiers on ACX Series Routers
- Schedulers Overview for ACX Series Routers
- Shared and Dedicated Buffer Memory Pools on ACX Series Routers
- CoS for PPP and MLPPP Interfaces on ACX Series Routers
- CoS for NAT Services on ACX Series Routers
- Hierarchical Class of Service in ACX Series Routers
- Storm Control on ACX Series Routers Overview
- play_arrow Configuring Class of Service on MX Series 5G Universal Routing Platforms
- Junos CoS on MX Series 5G Universal Routing Platforms Overview
- CoS Features and Limitations on MX Series Routers
- Configuring and Applying IEEE 802.1ad Classifiers
- Scheduling and Shaping in Hierarchical CoS Queues for Traffic Routed to GRE Tunnels
- Example: Performing Output Scheduling and Shaping in Hierarchical CoS Queues for Traffic Routed to GRE Tunnels
- CoS-Based Interface Counters for IPv4 or IPv6 Aggregate on Layer 2
- Enabling a Timestamp for Ingress and Egress Queue Packets
- play_arrow Configuring Class of Service on PTX Series Packet Transport Routers
- CoS Features and Limitations on PTX Series Routers
- CoS Feature Differences Between PTX Series Packet Transport Routers and T Series Routers
- Understanding Scheduling on PTX Series Routers
- Virtual Output Queues on PTX Series Packet Transport Routers
- Example: Configuring Excess Rate for PTX Series Packet Transport Routers
- Identifying the Source of RED Dropped Packets on PTX Series Routers
- Configuring Queuing and Shaping on Logical Interfaces on PTX Series Routers
- Example: Configuring Queuing and Shaping on Logical Interfaces in PTX Series Packet Transport Routers
- Example: Configuring Strict-Priority Scheduling on a PTX Series Router
- CoS Support on EVPN VXLANs
- Understanding CoS CLI Configuration Statements on PTX Series Routers
- Classification Based on Outer Header of Decapsulation Tunnel
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- play_arrow Configuring Line Card-Specific and Interface-Specific Functionality
- play_arrow Feature Support of Line Cards and Interfaces
- play_arrow Configuring Class of Service for Tunnels
- play_arrow Configuring Class of Service on Services PICs
- CoS on Services PICs Overview
- Configuring CoS Rules on Services PICs
- Configuring CoS Rule Sets on Services PICs
- Example: Configuring CoS Rules on Services PICs
- Packet Rewriting on Services Interfaces
- Multiservices PIC ToS Translation
- Fragmentation by Forwarding Class Overview
- Configuring Fragmentation by Forwarding Class
- Configuring Drop Timeout Interval for Fragmentation by Forwarding Class
- Example: Configuring Fragmentation by Forwarding Class
- Allocating Excess Bandwidth Among Frame Relay DLCIs on Multiservices PICs
- Configuring Rate Limiting and Sharing of Excess Bandwidth on Multiservices PICs
- play_arrow Configuring Class of Service on IQ and Enhanced IQ (IQE) PICs
- CoS on Enhanced IQ PICs Overview
- Calculation of Expected Traffic on IQE PIC Queues
- Configuring the Junos OS to Support Eight Queues on IQ Interfaces for T Series and M320 Routers
- BA Classifiers and ToS Translation Tables
- Configuring ToS Translation Tables
- Configuring Hierarchical Layer 2 Policers on IQE PICs
- Configuring Excess Bandwidth Sharing on IQE PICs
- Configuring Rate-Limiting Policers for High Priority Low-Latency Queues on IQE PICs
- Applying Scheduler Maps and Shaping Rate to Physical Interfaces on IQ PICs
- Applying Scheduler Maps to Chassis-Level Queues
- play_arrow Configuring Class of Service on Ethernet IQ2 and Enhanced IQ2 PICs
- CoS on Enhanced IQ2 PICs Overview
- CoS Features and Limitations on IQ2 and IQ2E PICs (M Series and T Series)
- Differences Between Gigabit Ethernet IQ and Gigabit Ethernet IQ2 PICs
- Shaping Granularity Values for Enhanced Queuing Hardware
- Ethernet IQ2 PIC RTT Delay Buffer Values
- Configuring BA Classifiers for Bridged Ethernet
- Setting the Number of Egress Queues on IQ2 and Enhanced IQ2 PICs
- Configuring the Number of Schedulers per Port for Ethernet IQ2 PICs
- Applying Scheduler Maps to Chassis-Level Queues
- CoS for L2TP Tunnels on Ethernet Interface Overview
- Configuring CoS for L2TP Tunnels on Ethernet Interfaces
- Configuring LNS CoS for Link Redundancy
- Example: Configuring L2TP LNS CoS Support for Link Redundancy
- Configuring Shaping on 10-Gigabit Ethernet IQ2 PICs
- Configuring Per-Unit Scheduling for GRE Tunnels Using IQ2 and IQ2E PICs
- Understanding Burst Size Configuration on IQ2 and IQ2E Interfaces
- Configuring Burst Size for Shapers on IQ2 and IQ2E Interfaces
- Configuring a CIR and a PIR on Ethernet IQ2 Interfaces
- Example: Configuring Shared Resources on Ethernet IQ2 Interfaces
- Configuring and Applying IEEE 802.1ad Classifiers
- Configuring Rate Limits to Protect Lower Queues on IQ2 and Enhanced IQ2 PICs
- Simple Filters Overview
- Configuring a Simple Filter
- play_arrow Configuring Class of Service on 10-Gigabit Ethernet LAN/WAN PICs with SFP+
- CoS on 10-Gigabit Ethernet LAN/WAN PIC with SFP+ Overview
- BA and Fixed Classification on 10-Gigabit Ethernet LAN/WAN PIC with SFP+ Overview
- DSCP Rewrite for the 10-Gigabit Ethernet LAN/WAN PIC with SFP+
- Configuring DSCP Rewrite for the 10-Gigabit Ethernet LAN/WAN PIC
- Queuing on 10-Gigabit Ethernet LAN/WAN PICs Properties
- Mapping Forwarding Classes to CoS Queues on 10-Gigabit Ethernet LAN/WAN PICs
- Scheduling and Shaping on 10-Gigabit Ethernet LAN/WAN PICs Overview
- Example: Configuring Shaping Overhead on 10-Gigabit Ethernet LAN/WAN PICs
- play_arrow Configuring Class of Service on Enhanced Queuing DPCs
- Enhanced Queuing DPC CoS Properties
- Configuring Rate Limits on Enhanced Queuing DPCs
- Configuring WRED on Enhanced Queuing DPCs
- Configuring MDRR on Enhanced Queuing DPCs
- Configuring Excess Bandwidth Sharing
- Configuring Customer VLAN (Level 3) Shaping on Enhanced Queuing DPCs
- Simple Filters Overview
- Configuring Simple Filters on Enhanced Queuing DPCs
- Configuring a Simple Filter
- play_arrow Configuring Class of Service on MICs, MPCs, and MLCs
- CoS Features and Limitations on MIC and MPC Interfaces
- Dedicated Queue Scaling for CoS Configurations on MIC and MPC Interfaces Overview
- Verifying the Number of Dedicated Queues Configured on MIC and MPC Interfaces
- Scaling of Per-VLAN Queuing on Non-Queuing MPCs
- Increasing Available Bandwidth on Rich-Queuing MPCs by Bypassing the Queuing Chip
- Flexible Queuing Mode
- Multifield Classifier for Ingress Queuing on MX Series Routers with MPC
- Example: Configuring a Filter for Use as an Ingress Queuing Filter
- Ingress Queuing Filter with Policing Functionality
- Ingress Rate Limiting on MX Series Routers with MPCs
- Rate Shaping on MIC and MPC Interfaces
- Per-Priority Shaping on MIC and MPC Interfaces Overview
- Example: Configuring Per-Priority Shaping on MIC and MPC Interfaces
- Configuring Static Shaping Parameters to Account for Overhead in Downstream Traffic Rates
- Example: Configuring Static Shaping Parameters to Account for Overhead in Downstream Traffic Rates
- Traffic Burst Management on MIC and MPC Interfaces Overview
- Understanding Hierarchical Scheduling for MIC and MPC Interfaces
- Configuring Ingress Hierarchical CoS on MIC and MPC Interfaces
- Configuring a CoS Scheduling Policy on Logical Tunnel Interfaces
- Per-Unit Scheduling and Hierarchical Scheduling for MPC Interfaces
- Managing Dedicated and Remaining Queues for Static CoS Configurations on MIC and MPC Interfaces
- Excess Bandwidth Distribution on MIC and MPC Interfaces Overview
- Bandwidth Management for Downstream Traffic in Edge Networks Overview
- Scheduler Delay Buffering on MIC and MPC Interfaces
- Managing Excess Bandwidth Distribution on Static Interfaces on MICs and MPCs
- Drop Profiles on MIC and MPC Interfaces
- Intelligent Oversubscription on MIC and MPC Interfaces Overview
- Jitter Reduction in Hierarchical CoS Queues
- Example: Reducing Jitter in Hierarchical CoS Queues
- CoS on Ethernet Pseudowires in Universal Edge Networks Overview
- CoS Scheduling Policy on Logical Tunnel Interfaces Overview
- Configuring CoS on an Ethernet Pseudowire for Multiservice Edge Networks
- CoS for L2TP LNS Inline Services Overview
- Configuring Static CoS for an L2TP LNS Inline Service
- CoS on Circuit Emulation ATM MICs Overview
- Configuring CoS on Circuit Emulation ATM MICs
- Understanding IEEE 802.1p Inheritance push and swap from a Transparent Tag
- Configuring IEEE 802.1p Inheritance push and swap from the Transparent Tag
- CoS on Application Services Modular Line Card Overview
- play_arrow Configuring Class of Service on Aggregated, Channelized, and Gigabit Ethernet Interfaces
- Limitations on CoS for Aggregated Interfaces
- Policer Support for Aggregated Ethernet Interfaces Overview
- Understanding Schedulers on Aggregated Interfaces
- Examples: Configuring CoS on Aggregated Interfaces
- Hierarchical Schedulers on Aggregated Ethernet Interfaces Overview
- Configuring Hierarchical Schedulers on Aggregated Ethernet Interfaces
- Example: Configuring Scheduling Modes on Aggregated Interfaces
- Enabling VLAN Shaping and Scheduling on Aggregated Interfaces
- Class of Service on demux Interfaces
- Example: Configuring Per-Unit Schedulers for Channelized Interfaces
- Applying Layer 2 Policers to Gigabit Ethernet Interfaces
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- play_arrow Configuration Statements and Operational Commands
Hierarchical Class of Service Overview
Hierarchical class of service (HCoS) is the ability to apply traffic schedulers and shapers to a hierarchy of scheduler nodes. Each level of the scheduler hierarchy can be used to shape traffic based on different criteria such as application, user, VLAN, slice, and physical port.
This allows you to support the requirements of different services, applications, and users on the same physical device and physical infrastructure.
HCoS is implemented primarily using traffic classifiers at the ingress and hierarchical schedulers and shapers at the egress.
A classifier is a filter that labels traffic at the device ingress based on configurable parameters such as application or destination. Traffic is classified into what is called a forwarding equivalence class (FEC). The FEC defines a class of traffic that receives common treatment.
Schedulers, and their associated shapers, are the functions that control the traffic bandwidth, jitter (delay variation), and packet loss priority at the egress of the device.
Hierarchical schedulers are used to apply multiple levels of scheduling and shaping with each level applied to different classifications such as forwarding equivalence class, VLAN, and physical interface (port) as shown in Figure 1.

Hierarchical class of service is also referred to as Hierarchical Quality of Service (HQoS) in other vendor’s documentation.
A typical application of HCoS is to configure multiple levels of egress schedulers and shapers, at the subscriber edge, using dynamic profiles to provide traffic shaping and prioritization at the subscriber VLAN level and for multiple classes of traffic.
Dynamic profiles are a mechanism that allows you to dynamically apply schedulers and shapers to individual subscribers or groups of subscribers.
To learn more about HCoS, the following topics are very helpful:
Junos CoS on MX Series 5G Universal Routing Platforms Overview
CoS Features of the Router Hardware, PIC, MIC, and MPC Interface Families
Hierarchical Class of Service for Subscriber Management Overview
The Junos OS hierarchical schedulers support up to five levels of scheduler hierarchies on MX Series devices when using enhanced queuing Dense Port Concentrators (DPCs) or fine-grained queuing Modular Port Concentrators (MPCs), and Modular Interface Cards (MICs). It is important to know the capabilities of your hardware with respect to HCoS. The following are a few tips to help you:
Only certain hardware supports the five-level scheduler hierarchy of HCoS.
The number of queues and logical interfaces supported is dependent upon exactly what hardware you are using.
The MX Series Packet Forwarding Engine handles guaranteed bandwidth and scheduler node weight differently than other Packet Forwarding Engines.
The fine-grained queuing MPCs and MICs have a certain granularity with respect to the shaping and delay buffer values. The values used are not necessarily exactly the values configured.
To learn more about platform support for HCoS, use the Juniper Networks Feature Explorer (https://pathfinder.juniper.net/feature-explorer/). In the Feature Explorer, search on hierarchical schedulers.
In addition, it is important to note the following:
HCoS is most frequently used to enforce service level agreements at the subscriber edged using dynamic traffic control profiles.
Hierarchical schedulers can also be applied to Ethernet pseudowire interfaces, aggregated Ethernet interfaces, Layer 2 Tunnel Protocol (L2TP) network server (LNS) inline services, and GRE tunnels.
Hierarchical ingress policing is a feature that is complimentary to and often used in conjunction with HCoS.
There are other features in Junos OS that have similar sounding names.
The hierarchical scheduler and shaper feature supported on the SRX Series Firewalls is not the HCoS feature described here.
Before planning HCoS for you network, you should learn about HCoS, define you needs, plan how you want to implement HCoS, and test the operation in a simulated environment.
Document | Description |
---|---|
Day One: Deploying Basic QoS Juniper Networks Books | This book is a good resource for learning the basics of CoS on Juniper Networks devices. |
Juniper MX-Series O'Reilly Media | Learn about the advanced features of HCoS. This book provides an in-depth description of how HCoS works and how it can be deployed. It also provides a lab tested topology and configuration example. |
Day One: Dynamic Subscriber Management Juniper Networks Books | Learn how to use HCoS in conjunction with dynamic traffic control profiles for subscriber management. This book also includes troubleshooting. |
QoS Enabled Networks John Wiley & Sons | This book is an additional source for studying QoS. |
Documentation related to HCoS is consolidated in the Hierarchical Class of Service User Guide.