Overview of CoS Changes Introduced in Junos OS Release 11.3

CoS Default Value Changes

The default values of the following CoS components have changed in Junos OS Release 11.3:

• Default Forwarding Classes
• Default IEEE 802.1p Unicast Classifiers
• Default IEEE 802.1p Multidestination Classifiers
• Default Scheduler

Queue Priority Configuration Changes

In Junos OS Release 11.1 and 11.2, you could configure strict-high priority queues with a guaranteed minimum bandwidth and configure forwarding class sets (priority groups) with a mix of low priority and strict-high priority queues. In Junos OS Release 11.3 and later, these configurations are invalid, and several other changes have also been implemented:

• Priority configuration in Junos OS Release 11.1 and 11.2 provided three priority levels: strict-high, high, and low. In Junos OS Release 11.3, the high priority option has been removed. Only the strict-high and low priority options are valid in Release 11.3.

• Minimum guaranteed bandwidth (transmit rate) is not allowed on strict-high priority queues. Minimum guaranteed bandwidth (guaranteed rate) is not allowed on forwarding class sets that contain strict-high priority queues.

• You cannot configure a multidestination queue as a strict-high priority queue. You cannot configure a queue as a strict-high priority queue if it belongs to the multidestination forwarding class set.

• Only one forwarding class set can contain strict-high priority queues. If you want to configure a strict-high priority queue, you must also configure a separate forwarding class set for the strict-high priority queue. A forwarding class set cannot contain a mixture of low priority and strict-high priority queues.

The rest of the queue priority characteristics remain the same as before. For example, you can configure only one queue as a strict-high priority queue.

Minimum Guaranteed Bandwidth (Transmit Rate and Guaranteed Rate) Changes

The following restrictions have been placed on minimum guaranteed bandwidth configuration in Junos OS Release 11.3:

• You cannot configure a guaranteed minimum bandwidth (transmit rate) for strict-high priority queues.

• Queues (forwarding classes) with a configured transmit rate cannot be included in a forwarding class set that has strict-high priority queues.

• You cannot configure a guaranteed minimum bandwidth (guaranteed rate) for forwarding class sets that include strict-high priority queues.

• For transmit rates below 1 Gbps, we recommend that you configure the transmit rate as a percentage instead of as a fixed rate. This is because the system converts fixed rates into percentages and may round small fixed rates to a lower percentage. For example, a fixed rate of 350 Mbps is rounded down to 3 percent instead of 3.5 percent.

Excess Rate Statement Disabled

The excess-rate statement has been disabled in Junos OS Release 11.3. Excess rate was used to specify the way extra bandwidth was shared among queues.

The excess-rate statement was used at the [edit class-of-service schedulers] hierarchy level for queue scheduling configuration and at the [edit class-of-service traffic-control-profiles] hierarchy level for forwarding class set scheduling configuration.

In Junos OS Release 11.3, extra bandwidth sharing among queues is proportional to the minimum guaranteed bandwidth (transmit rate) of the queue. Extra bandwidth sharing among forwarding class sets (priority groups) is proportional to the minimum guaranteed bandwidth (guaranteed rate) of the forwarding class set.

Queue Scheduling (Low and Strict-High Priority Queues)

In Junos OS Release 11.1 and 11.2, if you configured a guaranteed minimum bandwidth (transmit rate) for low-priority queues, the low-priority queues received their guaranteed minimum bandwidth from the same bandwidth pool as the strict-high priority queue, using round-robin scheduling. Until the minimum bandwidth requirements of all queues were met, the strict-high priority queue and low-priority queues that had a guaranteed minimum bandwidth were treated equally. After the minimum bandwidth requirements of all queues were met, the strict-high priority queue received as much of the leftover bandwidth as it needed. This meant that the only way to ensure that a strict-high priority queue received all of the bandwidth it needed was not to configure a guaranteed minimum bandwidth for other queues.

In Junos OS Release 11.3 and later, queue scheduling has changed so that queues receive bandwidth in the following sequence:

1. The strict-high priority queue receives all of the bandwidth it needs before any other queue is served. The strict-high priority queue can take the full port bandwidth if necessary and can starve other queues on the port.

2. The guaranteed minimum bandwidth (transmit rate) of low-priority queues is served until the minimum is met or the queues are empty.

3. All other low-priority queues and needs that exceed the minimum bandwidth are served.

Multidestination Traffic Changes

The changes to the default forwarding classes and classifiers affects multidestination traffic handling in Junos OS Release 11.3:

• The number of default multidestination forwarding classes has been reduced from four default multidestination forwarding classes in Junos OS Release 11.1 and 11.2 to one default multidestination in Release 11.3 (see Table 2).

• The default classifier configuration for multidestination traffic has changed so that there is now one default classifier for all multidestination traffic (see Table 6).

• By default, all IEEE 802.1p code points map to the default multidestination forwarding class.

• The default scheduler for multidestination traffic has changed so that there is now one default scheduler for all multidestination traffic (see Table 8).

• You cannot configure multidestination queues as strict-high priority queues and you cannot include strict-high priority queues in a forwarding class set that contains multidestination queues.