Associating the Scheduler Map with the Packet Forwarding Component Queues

On IQ interfaces, the traffic that is fed from the packet forwarding components into the PIC uses low PLP by default and is distributed evenly across the four chassis queues (not PIC queues), regardless of the scheduling configuration for each logical interface. This default behavior can cause traffic congestion.

To control the aggregated traffic transmitted from the chassis queues into the PIC, you can configure the chassis queues to derive their scheduling configuration from the associated logical interface’s. Include the scheduler-map-chassis derived statement at the [edit class-of-service interfaces type-fpc/pic] hierarchy level:

Caution: If you include the scheduler-map-chassis derived statement in the configuration, packet loss might occur when you subsequently add or remove logical interfaces at the [edit interfaces interface-name] hierarchy level. When fragmentation occurs on the egress interface, the first set of packet counters displayed in the output of the show interfaces queue command show the post-fragmentation values. The second set of packet counters (under the Packet Forwarding Engine Chassis Queues field) show the pre-fragmentation values. For more information about the show interfaces queue command, see the JUNOS Interfaces Command Reference.

You can include both the scheduler-map and the scheduler-map-chassis derived statements in the same interface configuration. The scheduler-map statement controls the scheduler inside the PIC, while the scheduler-map-chassis derived statement controls the aggregated traffic transmitted into the entire PIC. For the Gigabit Ethernet IQ PIC, include both statements.

For more information about the scheduler-map statement, see Associating the Scheduler Map with a Physical Interface. For information about logical interface scheduling configuration, see Associating the Scheduler Map and a Shaping Rate with a DLCI or VLAN.

Generally, when you include the scheduler-map-chassis statement in the configuration, you must use an interface wildcard for the interface name, as in type-fpc/pic/*. The wildcard must use this format—for example. so-1/2/*, which means all interfaces on FPC slot 1, PIC slot 2. There is one exception—you can apply the chassis scheduler map to a specific interface on the Gigabit Ethernet IQ PIC only.

According to JUNOS software wildcard rules, specific interface configurations override wildcard configurations. For chassis scheduler map configuration, this rule does not apply; instead, specific interface CoS configurations are added to the chassis scheduler map configuration. For more information about how wildcards work with chassis scheduler maps, see Examples: Scheduling Packet Forwarding Component Queues. For general information about wildcards, see the JUNOS System Basics Configuration Guide.

For more information, see the following sections:

• Assigning a Custom Scheduler to the Packet Forwarding Component Queues
• Examples: Scheduling Packet Forwarding Component Queues

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