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Understanding Default CoS Settings

If you do not configure CoS settings on the QFX Series, 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 attribute.

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)	3	no-loss
no-loss	Guaranteed delivery for TCP no-loss traffic (priority 4, IEEE 802.1p code point 100)	4	no-loss
network-control (nc)	Network control traffic (priority 7, IEEE 802.1p code point 111)	7	drop
mcast	Multidestination traffic	8	drop Note: You cannot configure multidestination forwarding classes as no-loss (lossless) traffic classes.

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 QFX Series applies default unicast IEEE 802.1, unicast DSCP, and multidestination 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. There are two different default unicast IEEE 802.1 classifiers, a trusted classifier for ports that are in trunk mode or tagged-access mode, and an untrusted classifier for ports that are in access mode.

Table 4 shows the default mapping of IEEE 802.1 code-point values to unicast forwarding classes and loss priorities for ports in trunk mode or tagged-access mode.

Table 4: Default IEEE 802.1 Unicast Classifiers for Ports in Trunk Mode or Tagged Access Mode (Trusted Classifier)

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 5 shows the default mapping of IEEE 802.1p code-point values to unicast forwarding classes and loss priorities for ports in access mode (all incoming traffic is mapped to best-effort forwarding classes).

Table 5: Default IEEE 802.1 Unicast Classifiers for Ports in Access Mode (Untrusted Classifier)

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 6 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 6: 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

Table 7 shows the default mapping of DSCP code-point values to unicast forwarding classes and loss priorities for DSCP IP and DCSP IPv6.

Table 7: Default DSCP IP and IPv6 Unicast Classifiers

Code Point	Forwarding Class	Loss Priority
ef (101110)	best-effort	low
af11 (001010)	best-effort	low
af12 (001100)	best-effort	low
af13 (001110)	best-effort	low
af21 (010010)	best-effort	low
af22 (010100)	best-effort	low
af23 (010110)	best-effort	low
af31 (011010)	best-effort	low
af32 (011100)	best-effort	low
af33 (011110)	best-effort	low
af41 (100010)	best-effort	low
af42 (100100)	best-effort	low
af43 (100110)	best-effort	low
be (000000)	best-effort	low
cs1 (001000)	best-effort	low
cs2 (010000)	best-effort	low
cs3 (011000)	best-effort	low
cs4 (100000)	best-effort	low
cs5 (101000)	best-effort	low
nc1 (110000)	network-control	low
nc2 (111000)	network-control	low

Note: There are no default DSCP IP or IPv6 classifiers for multidestination traffic. DSCP IPv6 classifiers are not supported for multidestination traffic.

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 8 shows the default drop profile configuration.

Table 8: Default Drop Profile

Fill Level	Drop Probability
100	100

Default Schedulers

Table 9 shows the default scheduler configuration.

Table 9: Default Schedulers

Default Scheduler and Queue Number	Guaranteed Rate (Minimum Bandwidth)	Shaping Rate (Maximum Bandwidth)	Excess Bandwidth Sharing	Priority	Buffer Size
Best-effort scheduler (queue 0)	5%	None	5%	low	5%
FCoE scheduler (queue 3)	35%	None	35%	low	35%
No-loss scheduler (queue 4)	35%	None	35%	low	35%
Network-control scheduler (queue 7)	5%	None	5%	low	5%
Multidestination scheduler (queue 8)	20%	None	20%	low	20%

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.

Default Scheduler Maps

Table 10 shows the default mapping of forwarding classes to schedulers.

Table 10: Default Scheduler Maps

Forwarding Class	Scheduler
best-effort	Default BE scheduler
fcoe	Default FCoE scheduler
no-loss	No-loss scheduler
network-control	Default network-control scheduler
mcast-be	Default multidestination scheduler

Default Shared Buffer Configuration

Table Table 11 and Table 12 show the default shared buffer allocations:

Table 11: Default Ingress Shared Buffer Configuration

Total Shared Ingress Buffer	Lossless Buffer	Lossless-Headroom Buffer	Lossy Buffer
100%	9%	45%	46%

Table 12: Default Egress Shared Buffer Configuration

Total Shared Egress Buffer	Lossless Buffer	Lossy Buffer	Multicast Buffer
100%	50%	31%	19%