close

keyboard_arrow_left

Table of Contents Expand all

list Table of Contents

English

Define Classifiers
Apply Classifiers to Incoming Packets on Interfaces
Define Policers to Limit Traffic and Control Congestion
Define Drop Profiles
Assign Each Forwarding Class to a Queue
Define Schedulers
Define Scheduler Maps
Define CoS Header Rewrite Rules
Apply Scheduler Maps and Rewrite Rules to Egress Interfaces
Change History Table

keyboard_arrow_right

Configuring Basic Packet Flow Through the Junos OS CoS Process

date_range 25-Sep-24

arrow_backward

arrow_forward

Figure 1 and Figure 2 show the components of the Junos OS CoS features, illustrating the sequence in which they interact.

Figure 1: CoS Classifier, Queues, and Scheduler

Figure 2: Packet Flow Through CoS- Configurable Components

The following configuration demonstrates the packet flow through the CoS process:

Define Classifiers

If you trust the CoS values in the packet headers, you can use behavior aggregate classification to map those values to a forwarding class and drop priority. For example:

content_copy zoom_out_map
[edit class-of-service]
classifiers { 
exp exp_classifier {
    forwarding-class data-queue {
        loss-priority high code-points 001;
        loss-priority low code-points 000;
    }
    forwarding-class nc-queue {
        loss-priority high code-points 111;
        loss-priority low code-points 110;
    }
    forwarding-class video-queue {
        loss-priority high code-points 011;
        loss-priority low code-points 010;
    }
    forwarding-class voice-queue {
        loss-priority high code-points 101;
        loss-priority low code-points 100;
    }
}

If you do not trust the CoS values in the packet headers, you can use the more complex multifield classification to map ingress traffic to a forwarding class and drop priority. For example:

content_copy zoom_out_map
[edit firewall]
family inet {
    filter classify {
        term sip {
            from {
                protocol [ udp tcp ];
                port 5060;
            }
            then {
                forwarding-class nc-queue;
                loss-priority low;
                accept;
            }
        }
    }
}

Apply Classifiers to Incoming Packets on Interfaces

You apply behavior aggregate classifiers to logical interfaces at the [edit class-of-service interfaces] hierarchy level. For example:

content_copy zoom_out_map
[edit class-of-service]
interfaces {  
    so-* {
        unit 0 {
            classifiers {
                exp exp_classifier;
            }
        }
    }
    t3-* {
        unit 0 {
            classifiers {
                exp exp_classifier;
            }
        }
    }
}

You apply multifield classifiers as input filters to logical interfaces at the [edit interfaces] hierarchy level. For example:

content_copy zoom_out_map
[edit interfaces]
fe-0/0/2 {
    unit 0 {
        family inet {
            filter {
                input classify;
            }
            address 10.12.0.13/30;
        }
    }
}

Define Policers to Limit Traffic and Control Congestion

If you need to rate-limit a traffic flow, either by discarding excess traffic (hard policing) or reassign excess traffic to a different forwarding class and/or loss priority (soft policing), define a policier and apply the policer to a firewall filter for that traffic flow. For example:

content_copy zoom_out_map
[edit firewall]
policer be-lp {
    if-exceeding {
        bandwidth-limit 10m;
        burst-size-limit 62500;
    }
    then loss-priority high;
}
family inet {
    filter be-lp {
        term t1 {
            from {
                protocol tcp;
                port 80;
            }
            then policer be-lp;
            then loss-priority low;
            then accept;
        }
    }
}

Define Drop Profiles

Use drop profiles to define the drop probabilities across the range of delay-buffer occupancy, supporting the random early detection (RED) process.

content_copy zoom_out_map
[edit class-of-service]
drop-profiles {
    be-red {
        fill-level 20 drop-probability 25;
        fill-level 30 drop-probability 50;
        fill-level 40 drop-probability 75;
        fill-level 50 drop-probability 100;
    }
}

Assign Each Forwarding Class to a Queue

To provide differentiated services to each forwarding class, assign each forwarding class to it’s own output queue. For example:

content_copy zoom_out_map
[edit class-of-service]
forwarding-classes {  
    queue 0 data-queue;
    queue 1 video-queue;
    queue 2 voice-queue;
    queue 3 nc-queue;
}

Define Schedulers

Define the scheduler characteristics for each forwarding class. For example:

content_copy zoom_out_map
[edit class-of-service]
schedulers {  # 
    data-scheduler {
        buffer-size percent 50;
        drop-profile-map loss-priority high protocol any drop-profile be-red;
        priority low;
        transmit-rate percent 50;
    }
    nc-scheduler {
        buffer-size percent 5;
        priority high;
        transmit-rate percent 5;
    }
    video-scheduler {
        buffer-size percent 25;
        priority strict-high;
        transmit-rate percent 25;
    }
    voice-scheduler {
        buffer-size percent 20;
        priority high;
        transmit-rate percent 20;
    }
}

Define Scheduler Maps

Use scheduler maps to map schedulers to forwarding classes. For example:

content_copy zoom_out_map
[edit class-of-service]
scheduler-maps {  
    sched1 {
        forwarding-class data-queue scheduler data-scheduler;
        forwarding-class nc-queue scheduler nc-scheduler;
        forwarding-class video-queue scheduler video-scheduler;
        forwarding-class voice-queue scheduler voice-scheduler;
    }
}

Define CoS Header Rewrite Rules

Use rewrite rules to redefine the CoS bit pattern of outgoing packets. For example:

content_copy zoom_out_map
[edit class-of-service]
rewrite-rules {
    inet-precedence inet-rewrite {
        forwarding-class data-queue {
            loss-priority high code-point 001;
            loss-priority low code-point 000;
        }
        forwarding-class nc-queue {
            loss-priority high code-point 111;
            loss-priority low code-point 110;
        }
        forwarding-class video-queue {
            loss-priority high code-point 101;
            loss-priority low code-point 100;
        }
        forwarding-class voice-queue {
            loss-priority high code-point 011;
            loss-priority low code-point 010;
        }
    }
}

Apply Scheduler Maps and Rewrite Rules to Egress Interfaces

content_copy zoom_out_map
[edit class-of-service]
interfaces {
    ge-* {
        scheduler-map sched1;
        unit * {
            rewrite-rules {
                inet-precedence inet-rewrite;
            }
        }
    }
}

Change History Table

Feature support is determined by the platform and release you are using. Use Feature Explorer to determine if a feature is supported on your platform.

Release

Description

21.2

Starting with Junos OS Release 21.2, Junos OS displays class of service configuration in alphabetical order regardless of configuration order.

arrow_backward PREVIOUS Packet Flow Through the Junos OS CoS Process Overview

NEXT arrow_forward Example: Classifying All Traffic from a Remote Device by Configuring Fixed Interface-Based Classification

Class of Service User Guide (Routers and EX9200 Switches)

ON THIS PAGE

Configuring Basic Packet Flow Through the Junos OS CoS Process

Define Classifiers

Apply Classifiers to Incoming Packets on Interfaces

Define Policers to Limit Traffic and Control Congestion

Define Drop Profiles

Assign Each Forwarding Class to a Queue

Define Schedulers

Define Scheduler Maps

Define CoS Header Rewrite Rules

Apply Scheduler Maps and Rewrite Rules to Egress Interfaces

Change History Table

Stay in touch

Helped me install or use the product
Accelerated my deployment

Discuss the product with a co-worker
Make a purchase inquiry

Class of Service User Guide (Routers and EX9200 Switches)

ON THIS PAGE

Configuring Basic Packet Flow Through the Junos OS CoS Process

Define Classifiers

See Also

Apply Classifiers to Incoming Packets on Interfaces

Define Policers to Limit Traffic and Control Congestion

See Also

Define Drop Profiles

Assign Each Forwarding Class to a Queue

See Also

Define Schedulers

See Also

Define Scheduler Maps

See Also

Define CoS Header Rewrite Rules

See Also

Apply Scheduler Maps and Rewrite Rules to Egress Interfaces

See Also

Related Documentation

Change History Table

Stay in touch