Understanding Hierarchical CoS for Subscriber Interfaces

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.

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.

Three-Level Hierarchical Scheduling

Three-level hierarchical scheduling is supported only on MX Series routers running MPC/MIC interfaces. 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.

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

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

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

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

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

Beginning with Junos OS Release 16.1, four-level hierarchical scheduling is supported on MX Series routers running NG-MPC2E, NG-MPC3E, MPC5, and MPC7 line cards. 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.

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. 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.

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.