Configuring CoS

date_range 18-Dec-24

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The traffic management class-of-service topics describe how to configure the Junos OS class-of-service (CoS) components. Junos CoS provides a flexible set of tools that enable you to fine tune control over the traffic on your network.

Define classifiers that classify incoming traffic into forwarding classes to place traffic in groups for transmission.
Map forwarding classes to output queues to define the type of traffic on each output queue.
Configure schedulers for each output queue to control the service level (priority, bandwidth characteristics) of each type of traffic.
Provide different service levels for the same forwarding classes on different interfaces.
On switches that support data center bridging standards, configure lossless transport across the Ethernet network using priority-based flow control (PFC), Data Center Bridging Exchange protocol (DCBX), and enhanced transmission selection (ETS) hierarchical scheduling.
Configure various CoS components individually or in combination to define CoS services.

Note:

When you change the CoS configuration or when you deactivate and then reactivate the CoS configuration, the system experiences packet drops because the system momentarily blocks traffic to change the mapping of incoming traffic to input queues. If you use a congestion notification profile for lossless behavior, you can expect the momentary generation of PFC pause frames.

Table 1 lists the primary CoS configuration tasks by platform and provides links to those tasks.

Note:

Links to features that are not supported on the platform for which you are looking up information might not be functional.

Table 1: CoS Configuration Tasks
CoS Configuration Task	Links
Basic CoS Configuration: Configure code-point aliases to assign a name to a pattern of code-point bits that you can use instead of the bit pattern when you configure CoS components such as classifiers and rewrite rules Configure classifiers and multidestination classifiers Set the forwarding class and loss priority of a packet based on the incoming CoS value and assign packets to output queues based on the associated forwarding class Change the host default output queue and mapping of DSCP bits used in the type of service (ToS) field Configure forwarding classes Configure rewrite rules to alter code point bit values in outgoing packets on the outbound interfaces of a switch so that the CoS treatment matches the policies of a targeted peer Configure Ethernet PAUSE flow control, a congestion relief feature that provides link-level flow control for all traffic on a full-duplex Ethernet link, including those that belong to Ethernet link aggregated (LAG) interfaces. On any particular interface, symmetric and asymmetric flow control are mutually exclusive. Assign the following CoS components to physical or logical interfaces: Classifiers Congestion notification profiles Forwarding classes Forwarding class sets Output traffic control profiles Port schedulers Rewrite rules	Defining CoS Code-Point Aliases Example: Configuring Classifiers Defining CoS BA Classifiers (DSCP, DSCP IPv6, IEEE 802.1p) Example: Configuring Multidestination (Multicast, Broadcast, DLF) Classifiers Changing the Host Outbound Traffic Default Queue Mapping Example: Configuring Forwarding Classes Defining CoS Rewrite Rules Enabling and Disabling CoS Symmetric Ethernet PAUSE Flow Control Configuring CoS Asymmetric Ethernet PAUSE Flow Control Assigning CoS Components to Interfaces
Configure Weighted random early detection (WRED) drop profiles that define the drop probability of packets of different packet loss probabilities (PLPs) as the output queue fills: Configure WRED drop profiles where you associate WRED drop profiles with loss priorities in a scheduler. When you map the scheduler to a forwarding class (queue), you apply the interpolated drop profile to traffic of the specified loss priority on that queue. Configure drop profile maps that map a drop profile to a packet loss priority, and associate the drop profile and packet loss priority with a scheduler Configure explicit congestion notification (ECN) to enable end-to-end congestion notification between two endpoints on TCP/IP based networks. Apply WRED drop profiles to forwarding classes to control how the switch marks ECN-capable packets.	Example: Configuring WRED Drop Profiles Example: Configuring Drop Profile Maps Example: Configuring ECN
Configure queue schedulers and the bandwidth scheduling priority of individual queues. Schedulers define the CoS properties of output queues (output queues are mapped to forwarding classes, and classifiers map traffic into forwarding classes based on IEEE 802.1p or DSCP code points). Queue scheduling works with priority group scheduling to create a two-tier hierarchical scheduler. CoS scheduling properties include the amount of interface bandwidth assigned to the queue, the priority of the queue, whether explicit congestion notification (ECN) is enabled on the queue, and the WRED packet drop profiles associated with the queue.	(Except QFX10000) Example: Configuring Queue Schedulers Example: Configuring Queue Scheduling Priority (QFX10000 only) Example: Configuring Queue Schedulers for Port Scheduling
Configure traffic control profiles to define the output bandwidth and scheduling characteristics of forwarding class sets (priority groups). The forwarding classes (queues) mapped to a forwarding class set share the bandwidth resources that you configure in the traffic control profile.	Defining CoS Traffic Control Profiles (Priority Group Scheduling) Example: Configuring Traffic Control Profiles (Priority Group Scheduling) Example: Configuring Minimum Guaranteed Output Bandwidth Example: Configuring Maximum Output Bandwidth
Configure enhanced transmission selection (ETS) and forwarding class sets, and disable the ETS recommendation TLV. Hierarchical port scheduling, the Junos OS implementation of ETS, enables you to group priorities that require similar CoS treatment into priority groups. You define the port bandwidth resources for a priority group, and you define the amount of the priority group’s resources that each priority in the group can use.	Example: Configuring Forwarding Class Sets Example: Configuring CoS Hierarchical Port Scheduling (ETS) (Except OCX1100)Disabling the ETS Recommendation TLV
Configure Data Center Bridging Capability Exchange protocol (DCBX), which discovers the data center bridging (DCB) capabilities of peers by exchanging feature configuration information and is an extension of the Link Layer Discovery Protocol (LLDP) Configure the DCBX mode that an interface uses to communicate with the connected peer Configure DCBX autonegotiation on a per-interface basis for each supported feature or application Define each application for which you want DCBX to exchange application protocol information Map applications to IEEE 802.1p code points Apply an application map to a DCBX interface	Example: Configuring DCBX Application Protocol TLV Exchange Configuring the DCBX Mode Configuring DCBX Autonegotiation Defining an Application for DCBX Application Protocol TLV Exchange Configuring an Application Map for DCBX Application Protocol TLV Exchange Applying an Application Map to an Interface for DCBX Application Protocol TLV Exchange
Configure CoS for FCoE: Configure priority-based flow control (PFC) to divide traffic on one physical link into eight priorities Configure a congestion notification profile (CNP) that enables priority-based flow control (PFC) on specified IEEE 802.1p priorities Configure Multichassis link aggregation groups (MC-LAGs) to provide redundancy and load balancing between two switches Configure two or more lossless forwarding classes and map them to different priorities Configure lossless FCoE transport if your network uses a different priority than 3 Configure multiple lossless FCoE priorities on a converged Ethernet network If the FCoE network uses a different priority than priority 3 for FCoE traffic, configure a rewrite value to remap incoming traffic from the FC SAN to that priority after the interface encapsulates the FC packets in Ethernet Configure lossless priorities for multiple types of traffic, such as FCoE and iSCSI	Example: Configuring CoS PFC for FCoE Traffic Example: Configuring CoS for FCoE Transit Switch Traffic Across an MC-LAG Configuring CoS PFC (Congestion Notification Profiles) Example: Configuring IEEE 802.1p Priority Remapping on an FCoE-FC Gateway Example: Configuring Two or More Lossless FCoE IEEE 802.1p Priorities on Different FCoE Transit Switch Interfaces Example: Configuring Lossless FCoE Traffic When the Converged Ethernet Network Does Not Use IEEE 802.1p Priority 3 for FCoE Traffic (FCoE Transit Switch) Example: Configuring Two or More Lossless FCoE Priorities on the Same FCoE Transit Switch Interface Configuring CoS Fixed Classifier Rewrite Values for Native FC Interfaces (NP_Ports) Example: Configuring Lossless IEEE 802.1p Priorities on Ethernet Interfaces for Multiple Applications (FCoE and iSCSI)

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Traffic Management User Guide (QFX Series Switches and EX4600 Switches)

Configuring CoS

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