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Applying Scheduler Maps to Chassis-Level Queues

 

On Intelligent Queuing (IQ) and Intelligent Queuing 2 (IQ2) interfaces, as well as on the 10x10GE MIC with SFP+, the traffic that is fed from the packet forwarding components into the PIC uses low packet loss priority (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.

The default chassis scheduler allocates resources for queue 0 through queue 3, with 25 percent of the bandwidth allocated to each queue. When you configure the chassis to use more than four queues, you must configure and apply a custom chassis scheduler to override the default chassis scheduler.

To apply a custom chassis scheduler:

  1. Specify the interface on which to apply the scheduler.

    For example:

  2. Specify the name of the custom scheduler you want to apply to the interface.

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.

To configure the chassis queues to derive their scheduling from the associated logical interfaces:

  1. Specify the logical interfaces from which to derive the scheduling configuration.

    For example:

  2. Specify that the scheduler configuration is derived from the specified logical interfaces.
Caution

If you specify 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 CLI Explorer.

You can specify 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.

Note

For the Gigabit Ethernet IQ PIC, you must specify both the scheduler-map and the scheduler-map-chassis derived statements in the interface configuration.

Generally, when you specify 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 OS wildcard rules, specific interface configurations override wildcard configurations. For chassis scheduler map configurations, 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 OS Administration Library.

Note

The interface applies wildcard configuration only if you do not add any specific configuration. If you add the specific interface configuration, then the interface deletes the applied wildcard configuration and applies the specified configuration.

For more information, see the following sections:

Applying Custom Schedulers to Packet Forwarding Component Queues

Optionally, you can apply a custom scheduler to the chassis queues instead of configuring the chassis queues to automatically derive their scheduling configuration from the logical interfaces on the PIC.

To apply a custom chassis scheduler:

  1. Specify the interface on which to apply the scheduler.

    For example:

  2. Specify the name of the custom scheduler you want to apply to the interface.

When you apply a custom scheduler map to packet forwarding component queues, or when you modify the configuration of a custom scheduler map that is already applied to packet forwarding component queues, packets already in the chassis queues might be dropped. The amount of packet loss is not deterministic and depends on the offered traffic load at the time you apply or modify the custom scheduler map.

Examples: Scheduling Packet Forwarding Component Queues

Example: Applying a Chassis Scheduler Map to a 2-Port IQ PIC

This example applies a chassis scheduler map to interfaces so-0/1/0 and so-0/1/1.

According to customary wildcard rules, the so-0/1/0 configuration overrides the so-0/1/* configuration, implying that the chassis scheduler map MAP1 is not applied to so-0/1/0. However, the wildcard rule is not obeyed in this case; the chassis scheduler map applies to both interfaces so-0/1/0 and so-0/1/1.

To configure the chassis queues to derive their scheduling from the associated logical interfaces:

  1. Specify the logical interfaces from which to derive the scheduling configuration.
  2. Using a wildcard rule, specify that the scheduler configuration is derived from the logical interfaces on so-0/1*.
  3. Review the configuration.
    user@host# show
  4. Save the configuration.

Not Recommended: Using a Wildcard for Gigabit Ethernet IQ Interfaces When Applying a Chassis Scheduler Map

On a Gigabit Ethernet IQ PIC, you can apply the chassis scheduler map at both the specific interface level and the wildcard level. We do not recommend this because the wildcard chassis scheduler map takes precedence, which might not be the desired effect. For example, if you want to apply the chassis scheduler map MAP1 to port 0 and MAP2 to port 1, we do not recommend the following:

user@host# show

Recommended: Identifying Gigabit Ethernet IQ Interfaces Individually When Applying a Chassis Scheduler Map

Instead, we recommend this configuration:

user@host# show

Example: Configuring ATM CoS with a Normal Scheduler and a Chassis Scheduler

For ATM2 IQ interfaces, the CoS configuration differs significantly from that of other interface types. For more information about ATM CoS, see CoS on ATM Interfaces Overview.

To configure scheduler mapping on ATM2 IQ interfaces:

  1. Apply the chassis scheduler to the ATM interface.
  2. Configure ATM-specific physical interface properties.
    1. Specify the ATM interface to configure.

    2. Configure the virtual path (VP).

    3. Specify the CoS virtual circuit drop profiles for random early detection (RED). These parameters define the drop preferences during times of congestion.

    4. Define the CoS parameters for the scheduler map.

  3. Configure the ATM logical interface.
    1. Specify the logical interface you want to configure.

    2. Specify the virtual circuit identifier (VCI) and virtual path identifier (VPI) for the ATM logical interfaces.

    3. Specify the traffic shaping profile parameters.

    4. Specify the scheduler map you want to associate with the ATM logical interface.

    5. Configure the protocol, local address, and remote address.

  4. Review the configuration.
    user@host# show
    user@host# show
  5. Save the configuration.

Example: Configuring Two T3 Interfaces on a Channelized DS3 IQ PIC

To configure two T3 interfaces on a channelized DS3 IQ PIC:

  1. Configure the first channelized DS3 IQ interface.
    1. Specify the name of the interface.

    2. Configure the interface as unpartitioned, clear channel.

  2. Configure the second channelized DS3 IQ interface.
    1. Specify the name of the interface.

    2. Configure the interface as unpartitioned, clear channel.

  3. Configure the first T3 channel.
    1. Specify the name of the T3 interface on the DS3 IQ PIC.

    2. Specify the protocol family and address of the interface.

  4. Configure the second T3 channel.
    1. Specify the name of the T3 interface on the DS3 IQ PIC.

    2. Specify the protocol family and address of the interface.

  5. Review the configuration.
    user@host# show
  6. Save the configuration.

Example: Applying Normal Schedulers to Two T3 Interfaces

Configure a scheduler for the aggregated traffic transmitted into both T3 interfaces.

  1. Specify the names of the scheduler maps for each interface.
  2. Specify the CoS parameters assigned to each forwarding class.
  3. Specify each scheduler name and the associated transmit rate..
  4. Review the configuration.
    user@host# show
  5. Save the configuration.

Example: Applying a Chassis Scheduler to Two T3 Interfaces

Bind a scheduler to the aggregated traffic transmitted into the entire PIC. The chassis scheduler controls the traffic from the packet forwarding components feeding the interface t3-3/0/*:

  1. Using a wildcard rule, specify that the scheduler configuration is derived from the logical interfaces on t3-3/0/*.
  2. Review the configuration.
    user@host# show
  3. Save the configuration.

Not Recommended: Using a Wildcard for Logical Interfaces When Applying a Scheduler

Do not apply a scheduler to a logical interface using a wildcard. For example, if you configure a logical interface (unit) with one parameter, and apply a scheduler map to the interface using a wildcard, the logical interface will not apply the scheduler. The following configuration will commit correctly but will not apply the scheduler map to interface so-3/0/0.0:

user@host# show

Recommended: Identifying Logical Interfaces Individually When Applying a Scheduler

Always apply the scheduler to a logical interface without the wildcard:

user@host# show
Note

This same wildcard behavior applies to classifiers and rewrites as well as schedulers.