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Understanding Default CoS Settings

 

If you do not configure CoS settings, Junos OS performs some CoS functions to ensure that traffic and protocol packets are forwarded with minimum delay when the network experiences congestion. Some default mappings are automatically applied to each logical interface that you configure.

You can display default CoS settings by issuing the show class-of-service operational mode command.

This topic describes the default configurations for the following CoS components:

Default Forwarding Classes and Queue Mapping

Table 1 shows the default mapping of the default forwarding classes to queues and packet drop attributes.

Table 1: Default Forwarding Classes and Queue Mapping

Default Forwarding Class

Description

Default Queue Mapping

Packet Drop Attribute

best-effort (be)

Best-effort traffic class (priority 0, IEEE 802.1p code point 000)

0

drop

fcoe

Guaranteed delivery for FCoE traffic (priority 3, IEEE 802.1p code point 011)

Note: Do not map traffic to the default fcoe forwarding class. Other switches use the fcoe forwarding class for Fibre Channel over Ethernet (FCoE) lossless Layer 2 transport, but OCX Series switches do not support FCoE or lossless Layer 2 transport.

3

no-loss

Note: The no-loss drop attribute is not supported on OCX Series switches. If you want to use queue 3, configure a new forwarding class without the no-loss packet drop attribute and map it to queue 3.

no-loss

Guaranteed delivery for TCP no-loss traffic (priority 4, IEEE 802.1p code point 100)

Note: Do not map traffic to the default no-loss forwarding class. Other switches use the no-loss forwarding class for lossless Layer 2 transport, but OCX Series switches do not support lossless Layer 2 transport.

4

no-loss

Note: The no-loss drop attribute is not supported on OCX Series switches. If you want to use queue 4, configure a new forwarding class without the no-loss packet drop attribute and map it to queue 4.

network-control (nc)

Network control traffic (priority 7, IEEE 802.1p code point 111)

7

drop

mcast

Multidestination traffic

8

drop

Note

On OCX Series switches only, do not map traffic to the default fcoe and no-loss forwarding classes. By default, the DSCP classifier does not map traffic to the fcoe and no-loss forwarding classes, so by default, the OCX Series does not classify traffic into those forwarding classes. (On other switches, the fcoe and no-loss forwarding classes provide lossless transport for Layer 2 traffic. OCX Series switches do not support lossless Layer 2 transport.)

Do not configure the no-loss packet drop attribute on a forwarding class, and do not map traffic to forwarding classes that have the no-loss attribute.

Default Forwarding Class Sets (Priority Groups)

If you do not explicitly configure forwarding class sets, the system automatically creates a default forwarding class set that contains all of the forwarding classes on the switch. The system assigns 100 percent of the port output bandwidth to the default forwarding class set.

Ingress traffic is classified based on the default classifier settings. The forwarding classes (queues) in the default forwarding class set receive bandwidth based on the default scheduler settings. Forwarding classes that are not part of the default scheduler receive no bandwidth.

The default forwarding class set is transparent. It does not appear in the configuration and is used for Data Center Bridging Capability Exchange (DCBX) protocol advertisement.

Default Code-Point Aliases

Table 2 shows the default mapping of code-point aliases to IEEE code points.

Table 2: Default IEEE 802.1 Code-Point Aliases

CoS Value Types

Mapping

be

000

be1

001

ef

010

ef1

011

af11

100

af12

101

nc1

110

nc2

111

Table 3 shows the default mapping of code-point aliases to DSCP and DSCP IPv6 code points.

Table 3: Default DSCP and DCSP IPv6 Code-Point Aliases

CoS Value Types

Mapping

ef

101110

af11

001010

af12

001100

af13

001110

af21

010010

af22

010100

af23

010110

af31

011010

af32

011100

af33

011110

af41

100010

af42

100100

af43

100110

be

000000

cs1

001000

cs2

010000

cs3

011000

cs4

100000

cs5

101000

nc1

110000

nc2

111000

Default Classifiers

The switch applies default classifiers to each interface that does not have explicitly configured classifiers. If you explicitly configure one type of classifier but not other types of classifiers, the system uses only the configured classifier and does not use default classifiers for other types of traffic.

Table 4 shows the default mapping of DSCP code-point values to unicast forwarding classes and loss priorities for DSCP IPv4 and DCSP IPv6. This is the default classifier used for Layer 3 IP traffic.

Table 4: Default DSCP IPv4 and IPv6 Unicast Classifiers

Code Point

Forwarding Class

Loss Priority

000000 (be)

best-effort

low

000001

best-effort

low

000010

best-effort

low

000011

best-effort

low

000100

best-effort

low

000101

best-effort

low

000110

best-effort

low

000111

best-effort

low

001000 (cs1)

best-effort

low

001001

best-effort

low

001010 (af11)

best-effort

low

001011

best-effort

low

001100 (af12)

best-effort

low

001101

best-effort

low

001110 (af13)

best-effort

low

001111

best-effort

low

010000 (cs2)

best-effort

low

010001

best-effort

low

010010 (af21)

best-effort

low

010011

best-effort

low

010100 (af22)

best-effort

low

010101

best-effort

low

010110 (af23)

best-effort

low

010111

best-effort

low

011000 (cs3)

best-effort

low

011001

best-effort

low

011010 (af31)

best-effort

low

011011

best-effort

low

011100 (af32)

best-effort

low

011101

best-effort

low

011110 (af33)

best-effort

low

011111

best-effort

low

100000 (cs4)

best-effort

low

100001

best-effort

low

100010 (af41)

best-effort

low

100011

best-effort

low

100100 (af42)

best-effort

low

100101

best-effort

low

100110 (af43)

best-effort

low

100111

best-effort

low

101000 (cs5)

best-effort

low

101001

best-effort

low

101011

best-effort

low

101100

best-effort

low

101101

best-effort

low

101110 (ef)

best-effort

low

101111

best-effort

low

110000 (nc1)

network-control

low

110001

network-control

low

110010

network-control

low

110011

network-control

low

110100

network-control

low

110101

network-control

low

110110

network-control

low

110111

network-control

low

111000 (nc2)

network-control

low

111001

network-control

low

111010

network-control

low

111011

network-control

low

111100

network-control

low

111101

network-control

low

111110

network-control

low

111111

network-control

low

Note

There are no default DSCP IPv4 or IPv6 classifiers for multidestination traffic. DSCP IPv6 classifiers are not supported for multidestination traffic.

Table 5 shows the DSCP IPv6 compatibility default classifier mappings.

Table 5: Default DSCP IPv6 Compatibility Classifiers

Code Point

Forwarding Class

Loss Priority

000000 (be)

best-effort

low

000001

best-effort

low

000010

best-effort

low

000011

best-effort

low

000100

best-effort

low

000101

best-effort

low

000110

best-effort

low

000111

best-effort

low

001000 (cs1)

best-effort

low

001001

best-effort

low

001010 (af11)

best-effort

low

001011

best-effort

low

001100 (af12)

best-effort

low

001101

best-effort

low

001110 (af13)

best-effort

low

001111

best-effort

low

010000 (cs2)

best-effort

low

010001

best-effort

low

010010 (af21)

best-effort

low

010011

best-effort

low

010100 (af22)

best-effort

low

010101

best-effort

low

010110 (af23)

best-effort

low

010111

best-effort

low

011000 (cs3)

best-effort

low

011001

best-effort

low

011010 (af31)

best-effort

low

011011

best-effort

low

011100 (af32)

best-effort

low

011101

best-effort

low

011110 (af33)

best-effort

low

011111

best-effort

low

100000 (cs4)

best-effort

low

100001

best-effort

low

100010 (af41)

best-effort

low

100011

best-effort

low

100100 (af42)

best-effort

low

100101

best-effort

low

100110 (af43)

best-effort

low

100111

best-effort

low

101000 (cs5)

best-effort

low

101001

best-effort

low

101011

best-effort

low

101100

best-effort

low

101101

best-effort

low

101110 (ef)

best-effort

low

101111

best-effort

low

110000 (nc1)

network-control

low

110001

best-effort

low

110010

best-effort

low

110011

best-effort

low

110100

best-effort

low

110101

best-effort

low

110110

best-effort

low

110111

best-effort

low

111000 (nc2)

network-control

low

111001

best-effort

low

111010

best-effort

low

111011

best-effort

low

111100

best-effort

low

111101

best-effort

low

111110

best-effort

low

111111

best-effort

low

Table 6 shows the default mapping of IEEE 802.1 code-point values to unicast forwarding classes and loss priorities.

Table 6: Default IEEE 802.1 Unicast Trusted 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

Table 7 shows the default mapping of IEEE 802.1p code-point values to unicast forwarding classes and loss priorities for untrusted ports.

Table 7: Default IEEE 802.1 Unicast Untrusted Classifiers

Code Point

Forwarding Class

Loss Priority

000

best-effort

low

001

best-effort

low

010

best-effort

low

011

best-effort

low

100

best-effort

low

101

best-effort

low

110

best-effort

low

111

best-effort

low

Table 8 shows the default mapping of IEEE 802.1 code-point values to multidestination (multicast, broadcast, and destination lookup fail traffic) forwarding classes and loss priorities.

Table 8: 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 Rewrite Rules

There are no default rewrite rules. If you do not explicitly configure rewrite rules, the switch does not reclassify egress traffic.

Default Drop Profile

Table 9 shows the default drop profile configuration.

Table 9: Default Drop Profile

Fill Level

Drop Probability

100

100

Default Schedulers

Table 10 shows the default scheduler configuration.

Table 10: Default Schedulers

Default Scheduler and Queue Number

Transmit Rate (Guaranteed Minimum Bandwidth)

Shaping Rate (Maximum Bandwidth)

Excess Bandwidth Sharing

Priority

Buffer Size

best-effort unicast forwarding class scheduler (queue 0)

5%

None

5%

low

5%

fcoe unicast forwarding class scheduler (queue 3)

35%

None

35%

low

35%

no-loss unicast forwarding class scheduler (queue 4)

35%

None

35%

low

35%

network-control unicast forwarding class scheduler (queue 7)

5%

None

5%

low

5%

mcast forwarding class scheduler (queue 8)

20%

None

20%

low

20%

Note

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

By default, only the best-effort and network-control unicast forwarding classes show in Table 10 have traffic mapped to them. Even though the default schedulers allocate 35 percent of the port bandwidth to the fcoe and no-loss forwarding classes, by default, no traffic is mapped (classified) to the fcoe and no-loss forwarding classes. Because the fcoe and no-loss forwarding classes carry no traffic, the bandwidth that the default schedulers assign to them can be used for the other forwarding classes.

Only the queues associated with the default schedulers receive default bandwidth, which is based on the default scheduler transmit rate. (You can configure schedulers and forwarding classes to allocate bandwidth to other queues or to change the default bandwidth of a default queue.) In addition, multidestination queue 11 receives enough bandwidth from the default multidestination scheduler to handle CPU-generated multidestination traffic.

Default hierarchical scheduling divides the total port bandwidth between two groups of traffic: unicast traffic and multidestination traffic. Unicast traffic receives and shares a total of 80 percent of the port bandwidth. By default, multidestination traffic (mcast queue 8) receives a total of 20 percent of the port bandwidth.

Note

Multidestination queue 11 also receives a small amount of default bandwidth from the multidestination scheduler. CPU-generated multidestination traffic uses queue 11, so you might see a small number of packets egress from queue 11. In addition, in the unlikely case that firewall filter match conditions map multidestination traffic to a unicast forwarding class, that traffic uses queue 11.

Default scheduling uses weighted round-robin (WRR) scheduling. Each queue receives a portion (weight) of the total available interface bandwidth. The scheduling weight is based on the transmit rate of the default scheduler for that queue. For example, queue 7 receives a default scheduling weight of 5 percent of the available bandwidth, and queue 4 receives a default scheduling weight of 35 percent of the available bandwidth. Queues are mapped to forwarding classes, so forwarding classes receive the default bandwidth for the queues to which they are mapped. Unused bandwidth is shared with other default queues.

If you want non-default (unconfigured) queues to forward traffic, you should explicitly map traffic to those queues (configure the forwarding classes and queue mapping) and create schedulers to allocate bandwidth to those queues. By default, unicast queues 1, 2, 5, and 6 are unconfigured, and multidestination queues 9, 10, and 11 are unconfigured. Unconfigured queues have a default scheduling weight of 1 so that they can receive a small amount of bandwidth in case they need to forward traffic. (However, queue 11 can use more of the default multidestination scheduler bandwidth if necessary to handle CPU-generated multidestination traffic.)

Note

All four multidestination queues have a scheduling weight of 1. Because by default multidestination traffic goes to queue 8, queue 8 receives almost all of the multidestination bandwidth. (There is no default traffic on queue 9 and queue 10, and very little default traffic on queue 11, so there is almost no competition for multidestination bandwidth.)

However, if you explicitly configure queue 9, 10, or 11 (by mapping code points to the unconfigured multidestination forwarding classes using the multidestination classifier), the explicitly configured queues share the multidestination scheduler bandwidth equally with default queue 8, because all of the queues have the same scheduling weight (1). To ensure that multidestination bandwidth is allocated to each queue properly and that the bandwidth allocation to the default queue (8) is not reduced too much, we strongly recommend that you configure a scheduler if you explicitly classify traffic into queue 9, 10, or 11.

If you map traffic to an unconfigured queue, the queue receives only the amount of group bandwidth proportional to its default weight (1). The actual amount of bandwidth an unconfigured queue receives depends on how much bandwidth the other queues in the group are using.

If the other unicast queues use less than their allocated amount of bandwidth, the unconfigured queues can share the unused bandwidth. Sharing unused bandwidth is one of the key advantages of hierarchical port scheduling. Configured queues have higher priority for bandwidth than unconfigured queues, so if a configured queue needs more bandwidth, then less bandwidth is available for unconfigured queues. Unconfigured queues always receive a minimum amount of bandwidth based on their scheduling weight (1). If you map traffic to an unconfigured queue, to allocate bandwidth to that queue, configure a scheduler for the forwarding class that is mapped to the queue.

Default Scheduler Maps

Table 11 shows the default mapping of forwarding classes to schedulers.

Table 11: Default Scheduler Maps

Forwarding Class

Scheduler

best-effort

Default BE scheduler

fcoe

Default FCoE scheduler

Note: OCX Series switches do not support FCoE traffic. By default, no traffic is mapped to this forwarding class. Do not map traffic to this default forwarding class.

no-loss

No-loss scheduler

Note: OCX Series switches do not support lossless Layer 2 traffic. By default, no traffic is mapped to this forwarding class. Do not map traffic to this default forwarding class.

network-control

Default network-control scheduler

mcast-be

Default multidestination scheduler

Default Shared Buffer Configuration

Table Table 12 and Table 13 show the default shared buffer allocations:

Table 12: Default Ingress Shared Buffer Configuration

Total Shared Ingress Buffer

Lossless Buffer

Lossless-Headroom Buffer

Lossy Buffer

100%

9%

45%

46%

Table 13: Default Egress Shared Buffer Configuration

Total Shared Egress Buffer

Lossless Buffer

Lossy Buffer

Multicast Buffer

100%

50%

31%

19%