Understanding Hierarchical CoS for Subscriber Interfaces

Hierarchical CoS enables you to apply traffic scheduling and queuing parameters and packet transmission scheduling parameters to an individual subscriber interface rather than to all interfaces configured on a port. Hierarchical CoS enables you to dynamically modify queues when subscribers require services.

Interfaces support up to a five-level CoS scheduling hierarchy that, when fully configured, generally consists of the physical interface (level 1), an interface set or underlying interface (level 2), one or more underlying logical interfaces (level 3), one or more session or customer VLANs (level 4), and one or more queues (level 5). Hierarchical scheduling configurations consist of the type of interfaces you configure—for example, a logical interface or an interface set—and where those interfaces reside in the scheduling hierarchy—level 2, level 3, or level 4. Because many hierarchical scheduling configurations are possible, we use the terms two-level hierarchical scheduling, three-level hierarchical scheduling, four-level hierarchical scheduling in this topic.

Two-Level Hierarchical Scheduling

Two-level hierarchical scheduling limits the number of hierarchical levels in the scheduling hierarchy to two as shown in Figure 1. In this configuration, interface sets are not configured and only the logical interfaces have traffic control profiles (TCPs). Configuring two levels of hierarchy on MPCs that support more levels preserves resources and allows the system to scale higher.

Figure 1: Two-Level Hierarchical Scheduling

In a two-level scheduling hierarchy, all logical interfaces and interface sets share a single node; no hierarchical relationship is formed.

You control two-level hierarchical scheduling by setting the maximum-hierarchy-levels option under the [edit interfaces interface-name hierarchical-scheduler] hierarchy to 2:

If the maximum-hierarchy-levels option is not set, then interface sets can be at either level 2 or level 3, depending on whether the member logical interfaces within the interface set have a traffic control profile.
If any member logical interface has a traffic-control profile, then the interface set is always a level 2 CoS scheduler node.
If no member logical interface has a traffic-control profile, the interface set is always a level 3 CoS scheduler node.
If the maximum-hierarchy-levels option is set, then the interface set can only be at level 3; it cannot be at level 2. In this case, if you configure a level 2 interface set, you generate Packet Forwarding Engine errors.

Table 1 summarizes the interface hierarchy and the CoS scheduler node levels for two-level hierarchical scheduling.

Table 1: Two-Level Hierarchical Scheduling—Interface Hierarchy Versus Scheduling Nodes
Level 1	Level 2	Level 3
Physical interface	Logical interface	One or more queues
Physical interface	Interface set	One or more queues

To configure two-level hierarchical scheduling, include the hierarchical-scheduler statement at the [edit interfaces interface-name] hierarchy level and set the maximum-hierarchy-levels option to 2.

CAUTION:

MPC3E, 32x10GE MPC4E, and 2x100GE + 8x10GE MPC4E MPCs support only two levels of scheduling hierarchy. When enabling hierarchical scheduling on these cards, you must explicitly set maximum-hierarchy-levels to 2.

Three-Level Hierarchical Scheduling

Three-level hierarchical scheduling supports up to eight CoS queues. You can configure many different three-level scheduling hierarchies, depending on the location of the interface set or the use of underlying interfaces. In all variations, the physical interface is a level 1 CoS scheduler node and the queues reside at the highest level. Configuring three levels of hierarchy on MPCs that support more levels preserves resources and allows the system to scale higher.

When you use three-level hierarchical scheduling, interface sets can reside at either level 3 or level 4. You can also configure an underlying logical interface at level 3 and a logical interface at level 4. Table 2 summarizes the most common cases of the interface hierarchy and the CoS scheduler node levels for three-level hierarchical scheduling.

Table 2: Three-Level Hierarchical Scheduling—Interface Hierarchy Versus CoS Scheduling Node Levels
Level 1	Level 2	Level 3	Level 4
Physical interface	Interface set	Logical interface	One or more queues
Physical interface	Logical interface	Interface set	One or more queues
Physical interface	Underlying logical interface	Logical interface	One or more queues

In three-level hierarchical scheduling, the CoS scheduler nodes at level 1, level 2, and level 3 form a hierarchical relationship.

With a three-level hierarchical scheduling, logical interfaces can reside at level 2, or they can reside at level 3 if the logical interface at level 2 is an underlying logical interface. This is shown in Figure 2.

Figure 2: Three-Level Hierarchical Scheduling—Logical Interfaces at Level 3 with Underlying Logical Interfaces at Level 2 Hierarchical structure of interfaces in a network with three levels: Logical Interface Level 3, Underlying Logical Interface Level 2 node, and Physical Interface Level 1 node. Connections show dependencies between levels.

Hierarchical structure of interfaces in a network with three levels: Logical Interface Level 3, Underlying Logical Interface Level 2 node, and Physical Interface Level 1 node. Connections show dependencies between levels.

Another possible configuration for three-level hierarchical scheduling is shown in Figure 3. In this configuration, the logical interfaces are located at level 2 and the interface sets are located at level 3.

Figure 3: Three-Level Hierarchical Scheduling—Logical Interfaces at Level 2 with Interface Sets at Level 3 Hierarchical structure of network interfaces: Level 3 nodes represent abstract units, Level 2 nodes are logical interfaces, and Level 1 nodes are physical hardware.

Hierarchical structure of network interfaces: Level 3 nodes represent abstract units, Level 2 nodes are logical interfaces, and Level 1 nodes are physical hardware.

To configure three-level hierarchical scheduling, include the implicit-hierarchy option at the [edit interfaces interface-name hierarchical-scheduler] hierarchy level and optionally set the maximum-hierarchy-levels option to 3. (The default value for maximum-hierarchy-levels is 3.)

Interface Hierarchy Versus CoS Hierarchy

An interface hierarchy and a CoS scheduling hierarchy are distinctly different. Interface hierarchy refers to the relationship between the various interfaces—for example, the relationship between logical interfaces and an interface set, the relationship between a logical interface and an underlying logical interface, or the relationship between the physical interface and the logical interface. CoS scheduling hierarchy refers to the hierarchical relationship between the CoS scheduler nodes. In two-level hierarchical scheduling, no hierarchy is formed between the CoS scheduler nodes—the logical interface and interface set share a single level 2 scheduler node. However, when you use the implicit-hierarchy option for three-level hierarchical scheduling, the CoS scheduler nodes form a scheduling hierarchy.

Figure 4 and Figure 5 provide two scenarios for this discussion. Figure 4 shows an interface hierarchy where a Gigabit Ethernet interface (ge-1/0/0) is the physical interface. Two logical interfaces (ge-1/0/0.100 and ge-1/0/0.101) are configured on the physical interface:

Logical interface ge-1/0/0.100 is a member of a PPPoE interface set and a Demux interface set.
Logical interface ge-1/0/0.101 is a member of a demux interface set.

Figure 4: Logical Interfaces at Level 2 and Interface Sets at Level 3 Hierarchical network diagram showing relationships between physical interfaces, logical interfaces, logical interface sets, and subscriber queues in a networking setup.

Hierarchical network diagram showing relationships between physical interfaces, logical interfaces, logical interface sets, and subscriber queues in a networking setup.

Each interface set has a dedicated queue. The CoS scheduler nodes at level 1 (physical interface), level 2 (underlying logical interfaces), and level 3 (interface sets) form a scheduling hierarchy.

To configure this scenario, you must include the implicit-hierarchy option under the hierarchical-scheduler statement on physical interface ge-1/0/0 and configure and apply traffic-control profiles on each interface set and underlying logical interface.

Figure 5 shows an interface hierarchy where Gigabit Ethernet interface ge-1/0/0 is the physical interface. Three logical interfaces are configured:

Two logical interfaces (Pp0.100 and Demux0.100) reside on the underlying logical interface ge-1/0/0.100.
A third logical interface (Pp0.101) resides on the underlying logical interface ge-1/0/0.101.

Figure 5: Logical Interfaces at Level 3 and Underlying Logical Interfaces at Level 2 Hierarchical network interface structure showing layers: L1 physical interface GE-1/0/0, L2 logical interfaces GE-1/0/0.100, L3 protocols PPPoE, Demux, DHCP, L4 subscriber queues managing traffic.

Hierarchical network interface structure showing layers: L1 physical interface GE-1/0/0, L2 logical interfaces GE-1/0/0.100, L3 protocols PPPoE, Demux, DHCP, L4 subscriber queues managing traffic.

Each logical interface has a dedicated queue. The CoS scheduler nodes at level 1 (physical interface), level 2 (underlying logical interfaces), and level 3 (logical interfaces) form a scheduling hierarchy.

To configure this scenario, you must include the implicit-hierarchy option under the hierarchical-scheduler statement on physical interface GE-1/0/0 and configure and apply traffic-control profiles on each logical interface and underlying logical interface.

You can configure many different three-level scheduling hierarchies; Figure 4 and Figure 5 present just two possible scenarios. Table 2 summarizes the possible interface locations and CoS scheduler nodes.

Four-Level Hierarchical Scheduling

Four-level hierarchical scheduling supports up to eight class of service queues. In four-level scheduling hierarchies, the physical interface is a level 1 CoS scheduler node and the queues reside at level 5.

Note:

Four-level hierarchical scheduling is not supported on agent circuit identifier (ACI) or aggregated Ethernet (AE) interfaces.

When you use four-level hierarchical scheduling, interface sets reside at levels 2 and 3 and logical interfaces reside at levels 3 and 4. Table 3 summarizes the most common case of the interface hierarchy and the CoS scheduler node levels for four-level hierarchical scheduling.

Table 3: Four-Level Hierarchical Scheduling—Interface Hierarchy Versus CoS Scheduling Node Levels
Level 1	Level 2	Level 3	Level 4	Level 5
Physical interface	Interface set	Customer VLAN (C-VLAN)	Session Logical Interface (ppp or dhcp)	One or more queues

In four-level hierarchical scheduling, the CoS scheduler nodes at level 1, level 2, level 3, and level 4 form a hierarchical relationship.

To configure four-level hierarchical scheduling, include the implicit-hierarchy option at the [edit interfaces interface-name hierarchical-scheduler] hierarchy level and set the maximum-hierarchy-levels option to 4.

Change History Table

Feature support is determined by the platform and release you are using. Use Feature Explorer to determine if a feature is supported on your platform.

Release

Description

19.3R1

Starting with Junos OS 19.3R1, you can apply an input traffic control profile (TCP) to a dynamic logical interface set in 4-level hierarchical scheduling or to two dynamic logical interface sets in 5-level hierarchical scheduling. Thus, Junos CoS enables you to dynamically assign a static input TCP with shaping-rate to a dynamic interface-set to enforce a customer’s SLA. If no such SLA enforcement is needed, you can configure a static TCP that is designated as the default input TCP assigned to any dynamic interface-set that does not already have an explicitly assigned input TCP.

18.4R1

Starting with Junos OS 18.4R1, you can apply dynamic and static logical interfaces in the same dynamic interface set on all MPCs that support 4 and 5-level hierarchical CoS. You can also apply dynamic interface sets in dynamic interface sets.

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