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Overview of CoS Changes Introduced in Junos OS Release 11.3

 

Junos OS Release 11.3 introduces many changes to class-of-service (CoS) functionality and to the CoS default values. This overview summarizes the changes, which other documents describe in detail.

Note

Some of the CoS changes are not backward compatible with Junos OS Releases 11.1 and 11.2. Overview of CoS Upgrade Requirements (Junos OS Release 11.1 or 11.2 to a Later Release) describes how to upgrade to Junos OS Release 11.3 if you have configured CoS on your QFX3500 switch.

This topic describes the following changes in CoS default values and behavior:

CoS Default Value Changes

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

Default Forwarding Classes

In Junos OS Releases 11.1 and 11.2, there were eight default forwarding classes, four unicast default forwarding classes and four default multidestination (multicast, broadcast, and destination lookup fail) forwarding classes. Table 1 shows the old default forwarding classes and default queue mapping:

Table 1: Junos OS Release 11.1 and 11.2 Default Forwarding Classes and Queue Mapping

Default Forwarding Class

Description

Default Queue Mapping

best-effort (be)

Unicast best-effort traffic

0

no-loss

Unicast guaranteed delivery for TCP no-loss traffic

2

fcoe

Unicast guaranteed delivery for FCoE traffic

3

network-control

Unicast network control traffic

7

multicast-best-effort (mcast-be)

Multidestination best-effort traffic

8

multicast-expedited-forwarding (mcast-ef)

Multidestination low-loss, low-latency traffic

9

multicast-assured-forwarding (mcast-af)

Multidestination assured forwarding traffic

10

multicast-network-control (mcast-nc)

Multidestination network control traffic

11

Junos OS Release 11.3 changes the default forwarding classes and queue mapping in the following ways:

  • Instead of eight default forwarding classes, there are five default forwarding classes.

  • The same four unicast default forwarding classes remain valid, but the default queue mapping of the no-loss forwarding class has changed from queue 2 to queue 4.

  • There is now only one default multidestination forwarding class instead of four default multidestination forwarding classes. All multidestination traffic is assigned by default to the default multidestination forwarding class.

Note

The rest of the forwarding class characteristics remain the same as before. For example, the QFX Series still supports 12 forwarding classes and 12 output queues. You can still configure a total of eight unicast forwarding classes and four multidestination forwarding classes. The unicast queues are still queues 0 through 7 and the multidestination queues are still queues 8 through 11. Unicast traffic must be mapped to unicast queues, and multidestination traffic must be mapped to multidestination queues. The queue to which a forwarding class is mapped determines whether the forwarding class is unicast or multidestination.

Table 2 shows the default forwarding classes and queue mapping in Junos OS 11.3 and later:

Table 2: Junos OS Release 11.3 Default Forwarding Classes and Queue Mapping

Default Forwarding Class

Description

Default Queue Mapping

best-effort (be)

Best-effort traffic class

0

fcoe

Guaranteed delivery for FCoE traffic

3

no-loss

Guaranteed delivery for TCP no-loss traffic

4

network-control (nc)

Network control traffic

7

mcast

Multicast traffic

8

Default IEEE 802.1p Unicast Classifiers

In Junos OS Release 11.1 and 11.2, there were default unicast classifiers only for best-effort and network-control traffic, as shown in Table 3:

Table 3: Junos OS Release 11.1 and 11.2 Default IEEE 802.1 Unicast Classifiers

Code Point

Forwarding Class

Loss Priority

be (000)

best-effort

low

be1 (001)

best-effort

low

ef (010)

best-effort

low

ef1 (011)

best-effort

low

af11 (100)

best-effort

low

af12 (101)

best-effort

low

nc1 (110)

network-control

low

nc2 (111)

network-control

low

Junos OS Release 11.3 introduces new default classifiers for FCoE and no-loss traffic, replacing the best-effort classifiers mapped to IEEE 802.1p code points 011 and 100, respectively, as shown in Table 4:

Table 4: Junos OS Release 11.3 Default IEEE 802.1 Unicast Classifiers

Code Point

Forwarding Class

Loss Priority

be (000)

best-effort

low

be1 (001)

best-effort

low

ef (010)

best-effort

low

ef1 (011)

fcoe

low

af11 (100)

no-loss

low

af12 (101)

best-effort

low

nc1 (110)

network-control

low

nc2 (111)

network-control

low

Default IEEE 802.1p Multidestination Classifiers

In Junos OS Release 11.1 and 11.2, there were default multidestination classifiers for best-effort and network-control traffic, as shown in Table 5:

Table 5: Junos OS Release 11.1 and 11.2 Default IEEE 802.1 Multidestination Classifiers

Code Point

Forwarding Class

Loss Priority

be (000)

mcast-be

low

be1 (001)

mcast-be

low

ef (010)

mcast-be

low

ef1 (011)

mcast-be

low

af11 (100)

mcast-be

low

af12 (101)

mcast-be

low

nc1 (110)

mcast-nc

low

nc2 (111)

mcast-nc

low

Junos OS Release 11.3 replaces the best-effort and network-control multidestination classifiers and maps all IEEE 802.1p code points to the new default multidestination forwarding class, as shown in Table 6:

Table 6: Junos OS Release 11.3 Default IEEE 802.1 Multidestination Classifiers

Code Point

Forwarding Class

Loss Priority

be (000)

mcast

low

be1 (001)

mcast

low

ef (010)

mcast

low

ef1 (011)

mcast

low

af11 (100)

mcast

low

af12 (101)

mcast

low

nc1 (110)

mcast

low

nc2 (111)

mcast

low

Default Scheduler

In Junos OS Release 11.1 and 11.2, there were four default schedulers:

  • Unicast best effort

  • Unicast network control

  • Multidestination best effort

  • Multidestination network control

Table 7 shows the default scheduler configuration in Junos OS Release 11.1 and 11.2:

Table 7: Junos OS Release 11.1 and 11.2 Default Schedulers

Default Scheduler and Queue Number

Guaranteed Rate (Minimum Bandwidth)

Shaping Rate (Maximum Bandwidth)

Excess Rate (Extra Bandwidth Sharing)

Priority

Best-effort scheduler (queue 0)

75%

None

25%

Low

Network-control scheduler (queue 7)

5%

None

25%

Low

Best-effort multidestination scheduler (queue 8)

15%

None

25%

Low

Network-control multidestination scheduler (queue 11)

5%

None

25%

Low

Junos OS Release 11.3 replaces the four old classifiers with five new classifiers:

  • Unicast best effort

  • FCoE

  • No loss

  • Unicast network control

  • Multidestination

There are now four different default unicast classifiers to provide default CoS for lossless queues (FCoE and no-loss traffic). Because there is only one default multidestination forwarding class in Junos OS Release 11.3, there is only one default multidestination classifier for all multidestination traffic. Also, the excess rate default value is removed from the scheduler because the excess-rate statement is no longer supported, as described elsewhere in this document. Table 8 shows the default scheduler configuration in Junos OS Releases 11.3:

Table 8: Default Schedulers

Default Scheduler and Queue Number

Guaranteed Rate (Minimum Bandwidth)

Shaping Rate (Maximum Bandwidth)

Excess Bandwidth Sharing

Priority

Best-effort scheduler (queue 0)

5%

None

5%

Low

FCoE scheduler (queue 3)

35%

None

35%

Low

No-loss scheduler (queue 4)

35%

None

35%

Low

Network-control scheduler (queue 7)

5%

None

5%

Low

Multidestination scheduler (queue 8)

20%

None

20%

Low

Note

The minimum guaranteed bandwidth rate also determines the amount of excess (extra) bandwidth that the queue can share. Extra bandwidth is allocated to queues in proportion to the minimum guaranteed bandwidth rate of each queue.

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.

Note

If you have configured strict-high or high priority queues in Junos OS Release 11.1 or 11.2, the changes in Release 11.3 are not backward compatible. Please read Overview of CoS Upgrade Requirements (Junos OS Release 11.1 or 11.2 to a Later Release) before you upgrade to Release 11.3.

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.

Note

If you have configured the excess-rate option in Junos OS Release 11.1 or 11.2, the changes in Release 11.3 are not backward compatible. Please read Overview of CoS Upgrade Requirements (Junos OS Release 11.1 or 11.2 to a Later Release) before you upgrade to Release 11.3.

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.