Configuring Up to 16 Custom Forwarding Classes
By default on many routers, four forwarding classes are mapped to four output queues, as shown in the topic Default Forwarding Classes. On these routers, you can configure more than four forwarding classes and queues; you can configure up to 16 forwarding classes and eight queues, with multiple forwarding classes assigned to single queues. The concept of assigning multiple forwarding classes to a queue is sometimes referred to as creating forwarding-class aliases.
You cannot use CoS-based forwarding features if you configure more than eight forwarding classes on the device.
Mapping multiple forwarding classes to single queues is useful. Suppose, for example,
that forwarding classes are set based on multifield packet classification, and the
multifield classifiers are different for core-facing interfaces and customer-facing
interfaces. Suppose you need four queues for a core-facing interface and five queues for
a customer-facing interface, where fc0 through fc4
correspond to the classifiers for the customer-facing interface, and
fc5 through fc8 correspond to classifiers for the
core-facing interface, as shown in Figure 1.
In this example, you need nine classifiers and, therefore, nine forwarding classes. The forwarding class-to-queue mapping is shown in Table 1.
|
Forwarding Class Names |
Queue Number |
|---|---|
|
|
0 |
|
|
1 |
|
|
2 |
|
|
3 |
|
|
4 |
To configure up to 16 forwarding classes, include the class and
queue-num statements at the [edit class-of-service
forwarding-classes] hierarchy level:
[edit class-of-service forwarding-classes] class class-name queue-num queue-number;
You can configure up 16 different forwarding-class names. The corresponding output queue
number can be from 0 through 7. Therefore, you can map multiple forwarding classes to a
single queue. If you map multiple forwarding classes to a queue, the multiple forwarding
classes must refer to the same scheduler (at the [edit class-of-service
scheduler-maps map-name forwarding-class
class-name scheduler
scheduler-name] hierarchy level).
When you configure up to 16 forwarding classes, you can use them as you can any other forwarding class—in classifiers, schedulers, firewall filters (multifield classifiers), policers, and rewrite rules.
When you configure up to 16 forwarding classes, the following limitations apply:
-
The
classandqueuestatements at the[edit class-of-service forwarding-classes]hierarchy level are mutually exclusive. In other words, you can include one or the other of the following configurations, but not both:[edit class-of-service forwarding-classes] queue queue-number class-name; [edit class-of-service forwarding-classes] class class-name queue-num queue-number;
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When you use CoS-based forwarding features, you cannot configure more than eight forwarding classes with a forwarding policy. However, if you try to configure CoS-based forwarding with more than eight forwarding classes configured, commit fails with a message. Therefore, you can configure CBF on a router with eight or less than eight forwarding classes only. Under this condition, the forwarding class to queue mapping can be either one-to-one or one-to-many.
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A scheduler map that maps eight different forwarding classes to eight different schedulers can only be applied to interfaces that support eight queues. If you apply this type of scheduler map to an interface that only supports four queues, then the commit fails.
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We recommend that you configure the statements changing PICs to support eight queues and then applying an eight queue scheduler map in two separate steps. Otherwise, the commit might succeed but the PIC might not have eight queues when the scheduler map is applied, generating an error.
You can determine the ID number assigned to a forwarding class by issuing the
show class-of-service forwarding-class command. You can determine
whether the classification is fixed by issuing the show class-of-service
forwarding-table classifier mapping command. In the command output, if the
Table Type field appears as Fixed, the
classification is fixed. For more information about fixed classification, see Applying Forwarding
Classes to Interfaces.
Enabling Eight Queues on Interfaces
By default, some routers are restricted to a maximum of four egress queues per interface. The following procedures describe how to configure a maximum of eight egress queues on these interfaces.
In addition to configuring eight queues at the [edit
chassis] hierarchy level, the configuration at the
[edit class-of-service] hierarchy level must support
eight queues per interface.
The maximum number of queues per PIC can be 4 or
8. If you include the
max-queues-per-interface statement, all ports on the PIC
use configured mode and all interfaces on the IQ PIC have the same maximum
number of queues.
To configure a maximum of eight egress queues on these PICs:
To determine how many queues an interface supports, you can check the
CoS queues output field of the show interfaces
interface-name extensive command:
To view how many queues an interface supports:
user@host> show interfaces so-1/0/0 extensive CoS queues: 8 supported
If you include the max-queues-per-interface 4 statement, you can
configure all four ports and configure up to four queues per port.
When you include the max-queues-per-interface statement and
commit the configuration, all physical interfaces on the PIC are deleted and
re-added. Also, the PIC is taken offline and then brought back online
immediately. You do not need to take the PIC offline and online manually. You
should change modes between four queues and eight queues only when there is no
active traffic going to the PIC.
Assigning Multiple Forwarding Classes and Default Forwarding Classes
For queues 0 through 3, if you assign multiple forwarding classes to a single queue, default forwarding class assignment works as follows:
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The first forwarding class that you assign to queue 0 acquires the default BE classification and scheduling.
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The first forwarding class that you assign to queue 1 acquires the default EF classification and scheduling.
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The first forwarding class that you assign to queue 2 acquires the default AF classification and scheduling.
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The first forwarding class that you assign to queue 3 acquires the default NC classification and scheduling.
Of course you can override the default classification and scheduling by configuring custom classifiers and schedulers.
If you do not explicitly map forwarding classes to queues 0 through 3, then the respective default classes are automatically assigned to those queues. When you are counting the 16 forwarding classes, you must include in the total any default forwarding classes automatically assigned to queues 0 through 3. As a result, you can map up to 13 forwarding classes to a single queue when the single queue is queue 0, 1, 2, or 3. You can map up to 12 forwarding classes to a single queue when the single queue is queue 4, 5, 6, or 7. In summary, there must be at least one forwarding class each (default or otherwise) assigned to queue 0 through 3, and you can assign the remaining 12 forwarding classes (16–4) to any queue.
For example, suppose you assign two forwarding classes to queue 0 and you assign no forwarding classes to queues 1 through 3. The software automatically assigns one default forwarding class each to queues 1 through 3. This means 11 forwarding classes (16–5) are available for you to assign to queues 4 through 7.
For more information about forwarding class defaults, see Default Forwarding Classes.
Examples: Configuring Up to 16 Forwarding Classes
To configure 16 forwarding classes, map two forwarding classes to each queue. For example:
[edit] user@host# edit class-of-service forwarding-classes user@host# set class fc0 queue-num 0 user@host# set class fc1 queue-num 0 user@host# set class fc2 queue-num 1 user@host# set class fc3 queue-num 1 user@host# set class fc4 queue-num 2 user@host# set class fc5 queue-num 2 user@host# set class fc6 queue-num 3 user@host# set class fc7 queue-num 3 user@host# set class fc8 queue-num 4 user@host# set class fc9 queue-num 4 user@host# set class fc10 queue-num 5 user@host# set class fc11 queue-num 5 user@host# set class fc12 queue-num 6 user@host# set class fc13 queue-num 6 user@host# set class fc14 queue-num 7 user@host# set class fc15 queue-num 7
For PICs restricted to four queues, map four forwarding classes to each queue:
Specify each forwarding class and queue you want mapped.
[edit] user@host# edit class-of-service restricted-queues user@host# set forwarding-class fc0 queue 0 user@host# set forwarding-class fc1 queue 0 user@host# set forwarding-class fc2 queue 0 user@host# set forwarding-class fc3 queue 0 user@host# set forwarding-class fc4 queue 1 user@host# set forwarding-class fc5 queue 1 user@host# set forwarding-class fc6 queue 1 user@host# set forwarding-class fc7 queue 1 user@host# set forwarding-class fc8 queue 2 user@host# set forwarding-class fc9 queue 2 user@host# set forwarding-class fc10 queue 2 user@host# set forwarding-class fc11 queue 2 user@host# set forwarding-class fc12 queue 3 user@host# set forwarding-class fc13 queue 3 user@host# set forwarding-class fc14 queue 3 user@host# set forwarding-class fc15 queue 3
If you map multiple forwarding classes to a queue, the multiple forwarding classes must refer to the same scheduler. To configure a scheduler map applicable to an interface restricted to four queues:
Specify a scheduler map name and associate it with the scheduler configuration and forwarding class.
[edit] user@host# edit class-of-service scheduler-maps interface-restricted user@host# set forwarding-class be scheduler 00 user@host# set forwarding-class ef scheduler Q1 user@host# set forwarding-class ef1 scheduler Q1 user@host# set forwarding-class ef2 scheduler Q1 user@host# set forwarding-class af1 scheduler Q2 user@host# set forwarding-class af scheduler Q2 user@host# set forwarding-class nc scheduler Q3 user@host# set forwarding-class nc1 scheduler Q3
Map the forwarding classes to the restricted queues.
[edit] user@host# edit class-of-service restricted-queues user@host# set forwarding-class be queue 0 user@host# set forwarding-class ef queue 1 user@host# set forwarding-class ef1 queue 1 user@host# set forwarding-class ef2 queue 1 user@host# set forwarding-class af queue 2 user@host# set forwarding-class af1 queue 2 user@host# set forwarding-class nc queue 3 user@host# set forwarding-class nc1 queue 3