Modular QoS Configuration Guide for Cisco NCS 540 Series Routers, Cisco IOS XR Release 7.4.x - Configuring Modular QoS Congestion Management [Cisco Network Convergence System 540 Series Routers] (2024)

This chapter covers the following topics:

Congestion Management Overview

Congestion management features allow you to control congestion by determining the order in which a traffic flow (or packets) is sent out an interface based on priorities assigned to packets. Congestion management entails the creation of queues, assignment of packets to those queues based on the classification of the packet, and scheduling of the packets in a queue for transmission.

The types of traffic regulation mechanisms supported are:

Class-based Weighted Fair Queueing
Low-Latency Queuing with Strict Priority Queuing
Traffic Shaping
Traffic Policing

Class-based Weighted Fair Queueing

Class-based Weighted Fair Queueing (CBWFQ) allows definition of traffic classes based on customer match criteria. With CBWFQ you can define traffic classes and assign guaranteed amount of minimum bandwidth to them. CBWFQ also allows for a strict priority queue for delay-sensitive traffic.

Bandwidth Remaining

The CBWFQ algorithm derives the weight for each class from the bandwidth remaining value allocated to the class. The bandwidth remaining option specifies a weight for the class to the CBWFQ . After the priority-queue is serviced, the leftover bandwidth is distributed as per bandwidth remaining ratio (BWRR) or percentage. If you do not configure this command for any class, the default value of the BWRR is considered as 1 (one). In the case of bandwidth remaining percent , the remaining bandwidth is equally distributed among other classes, to make it 100 percentage (100%).

Restrictions

The bandwidth remaining command is supported only for egress policies.

Configuring Bandwidth Remaining

Supported Platforms: Cisco NCS 540 Series Routers.

This procedure configures the minimum bandwidth and bandwidth remaining on the router

Modular QoS Configuration Guide for Cisco NCS 540 Series Routers, Cisco IOS XR Release 7.4.x - Configuring Modular QoS Congestion Management [Cisco Network Convergence System 540 Series Routers] (1)

Note

The bandwidth , bandwidth remaining , shaping , queue-limit and wred commands may be configured together in the same class. But, priority cannot be configured along with bandwidth , bandwidth remaining and wred commands.

You can configure shape average command along with priority command.

Configuration Example

You have to accomplish the following to complete the bandwidth remaining configuration:

Creating or modifying a policy-map that can be attached to one or more interfaces
Specifying the traffic class whose policy has to be created or changed
Allocating the leftover bandwidth for the class
Attaching the policy-map to an output interface

Router# configureRouter(config)#class-map qos-6 Router(config-cmap)#match traffic-class 4 Router(config-cmap)#exitRouter(config-cmap)#commitRouter(config)#class-map qos-5 Router(config-cmap)#match traffic-class 5 Router(config-cmap)#commitRouter(config)# policy-map test-bw-bw-remRouter(config-pmap)# class qos-6Router(config-pmap-c)# bandwidth percent 60Router(config-pmap-c)# bandwidth remaining percent 60Router(config-pmap)#class qos-5Router(config-pmap-c)#bandwidth percent 20Router(config-pmap-c)#bandwidth remaining percent 40Router(config-pmap-c# exitRouter(config-pmap)# exitRouter(config)# interface HundredGigE 0/6/0/18Router(config-if)# service-policy output test-bw-bw-remRouter(config-if)# commit

Running Configuration

policy-map test-bw-bw-rem class qos-6 bandwidth percent 60 bandwidth remaining percent 60 ! class qos-5 bandwidth percent 20 bandwidth remaining percent 40 ! class class-default ! end-policy-map!interface HundredGigE0/6/0/18 service-policy output test-bw-bw-rem!

Verification

Router# show qos interface HundredGigE 0/6/0/18 outputNOTE:- Configured values are displayed within parenthesesInterface HundredGigE0/6/0/18 ifh 0x3000220 -- output policyNPU Id: 3Total number of classes: 3Interface Bandwidth: 100000000 kbpsVOQ Base: 11176VOQ Stats Handle: 0x88550ea0Accounting Type: Layer1 (Include Layer 1 encapsulation and above)------------------------------------------------------------------------------Level1 Class = qos-6Egressq Queue ID = 11182 (LP queue)Queue Max. BW. = 100824615 kbps (default)Queue Min. BW. = 60494769 kbps (60 %)Inverse Weight / Weight = 2 (60%)Guaranteed service rate = 71881188 kbpsTailDrop Threshold = 90177536 bytes / 10 ms (default)WRED not configured for this classLevel1 Class = qos-5Egressq Queue ID = 11181 (LP queue)Queue Max. BW. = 100824615 kbps (default)Queue Min. BW. = 20164923 kbps (20 %)Inverse Weight / Weight = 3 (40%)Guaranteed service rate = 27920792 kbpsTailDrop Threshold = 35127296 bytes / 10 ms (default)WRED not configured for this classLevel1 Class = class-defaultEgressq Queue ID = 11176 (Default LP queue)Queue Max. BW. = 101803495 kbps (default)Queue Min. BW. = 0 kbps (default)Inverse Weight / Weight = 120 (BWR not configured)Guaranteed service rate = 198019 kbpsTailDrop Threshold = 247808 bytes / 10 ms (default)WRED not configured for this class

Associated Commands

bandwidth remaining

Low-Latency Queuing with Strict Priority Queuing

The Low-Latency Queuing (LLQ) feature brings strict priority queuing (PQ) to the CBWFQ scheduling mechanism. Priority queuing (PQ) in strict priority mode ensures that one type of traffic is sent, possibly at the expense of all others. For PQ, a low-priority queue can be detrimentally affected, and, in the worst case, never allowed to send its packets if a limited amount of bandwidth is available or the transmission rate of critical traffic is high.

Configuring Low Latency Queuing with Strict Priority queuing

Configuring low latency queuing (LLQ) with strict priority queuing (PQ) allows delay-sensitive data such as voice to be de-queued and sent before the packets in other queues are de-queued.

Guidelines

Only priority level 1 to 7 is supported, with 1 being the highest priority and 7 being the lowest. However, the default CoSQ 0 has the lowest priority among all.
Priority level 1 to 7 is supported for non-H-QoS profiles, with 1 being the highest priority and 7 being the lowest. For H-QoS profiles, priority level 1 to 4 is supported. For all profiles, however, the class default is CoSQ 0 and has the lowest priority among all.
Egress policing is not supported. Hence, in the case of strict priority queuing, there are chances that the other queues do not get serviced.
You can configure shape average and queue-limit commands along with priority .
You can configure shape average , random-detect , and queue-limit commands along with priority .

Configuration Example

You have to accomplish the following to complete the LLQ with strict priority queuing:

Creating or modifying a policy-map that can be attached to one or more interfaces
Specifying the traffic class whose policy has to be created or changed.
Specifying priority to the traffic class
(Optional) Shaping the traffic to a specific bit rate
Attaching the policy-map to an output interface

Router# configureRouter(config)#class-map qos-1Router(config-cmap)#match traffic-class 1 Router(config-cmap)#commitRouter(config)#class-map qos-2 Router(config-cmap)#match traffic-class 2 Router(config-cmap)#commitRouter(config)# policy-map test-priority-1Router(config-pmap)# class qos1Router(config-pmap-c)# priority level 7Router(config-pmap-c)# shape average percent 2 Router(config-pmap-c)# class qos-2Router(config-pmap-c)# priority level 6Router(config-pmap-c)# shape average percent 1 Router(config-pmap-c)# commit Router(config-pmap-c# exitRouter(config-pmap)# exitRouter(config)# interface HundredGigE 0/0/0/20Router(config-if)# service-policy output test-priority-1Router(config-if)# commit

Running Configuration

policy-map test-priority-1 class qos-1 priority level 7 shape average percent 2 ! class qos-2 priority level 6 shape average percent 1 ! class class-default ! end-policy-map!interface HundredGigE0/0/0/20 service-policy output test-priority-1!

Verification

Router#  show qos int hundredGigE 0/0/0/20 outputNOTE:- Configured values are displayed within parenthesesInterface HundredGigE0/0/0/20 ifh 0x38 -- output policyNPU Id: 0Total number of classes: 3Interface Bandwidth: 100000000 kbpsPolicy Name: test-priority-1VOQ Base: 1184Accounting Type: Layer1 (Include Layer 1 encapsulation and above)------------------------------------------------------------------------------Level1 Class (HP7) = qos-1Egressq Queue ID = 1185 (HP7 queue)Queue Max. BW. = 2000000 kbps (2 %)Guaranteed service rate = 2000000 kbpsPeak burst = 36864 bytes (default)TailDrop Threshold = 2499840 bytes / 10 ms (default)WRED not configured for this classLevel1 Class (HP6) = qos-2Egressq Queue ID = 1186 (HP6 queue)Queue Max. BW. = 1000000 kbps (1 %)Guaranteed service rate = 1000000 kbpsPeak burst = 36864 bytes (default)TailDrop Threshold = 1249792 bytes / 10 ms (default)WRED not configured for this classLevel1 Class = class-defaultEgressq Queue ID = 1184 (Default LP queue)Queue Max. BW. = no max (default)Queue Min. BW. = 0 kbps (default)Inverse Weight / Weight = 1 / (BWR not configured)Guaranteed service rate = 97000000 kbpsPeak burst = 36864 bytes (default)TailDrop Threshold = 121249792 bytes / 10 ms (default)WRED not configured for this class

Associated Commands

priority

Overhead Accounting

Traffic shapers and policers use packet traffic descriptors to ensure adherence to the service level agreement in QoS. However, when traffic flows from one hop to another in a network, headers added or removed at interim hops affect the packet bytes being accounted for by QoS at each hop. When your end-user network measures the packet bytes to ensure they receive the payload as agreed, these additional header bytes cause a discrepancy.

QoS overhead accounting provides the flexibility to operators to decide which header bytes can be excluded by the traffic shaper and policer and which can be included, depending on the end user’s requirements and device capabilities, to meet the committed payload in units of bytes.

For example, if the QoS commitment includes the additional header bytes, the overhead accounting feature allows your router to account for this overhead and reduces the traffic policing and shaping rates accordingly. This is also called a positive accounting overhead.

If however, the committed rate doesn’t include the additional bytes, overhead accounting allows your router to adjust the core stream traffic such that the traffic policing and shaping rates are increased. This is also called a negative accounting overhead.

To summarize, QoS overhead accounting enables the router to account for packet overhead when shaping and policing traffic to a specific rate. This accounting ensures that the router runs QoS features on the actual bandwidth that the subscriber traffic consumes.

Any interface that supports QoS policies supports overhead accounting.

Note

You can enable user overhead accounting using the optional configuration of accounting user-defined <overhead size in bytes> while attaching the service policy on the egress interface.

Guidelines and Restrictions

Overhead accounting for ingress shaping is not supported.
You can't program more than one compensation value per NPU or router, even if they're on different egress ports.
You can configure the same egress compensation for different egress ports.

Configuring for Overhead Accounting

To configure overhead accounting, you must:

Create a policy map and configure QoS actions for that map.
Configure overhead accounting and attach the map to an interface.

/* create QoS policy */Router#configure terminalRouter(config)#policy-map policerRouter(config-pmap)#class class-defaultRouter(config-pmap-c)#police rate percent 10Router(config-pmap-c-police)#commit

/* configure account overhead value while attaching the QoS policy to interface */Router(config)#int hundredGigE 0/0/0/2 Router(config-if)#service-policy input policer account user-defined 12Router(config-if)#commitRouter(config-if)#rootRouter(config)#end

Running Configuration

Router#sh run int hundredGigE 0/0/0/2interface HundredGigE0/0/0/2service-policy input policer account user-defined 12!

The following example shows how to configure a negative overhead accounting value:

Router#confRouter(config)#int hundredGigE 0/0/0/2Router(config-if)#service-policy input policer account user-defined -12Router(config-if)#commit

To modify an overhead accounting value, you must:

Router#confRouter(config)#int hundredGigE 0/0/0/2Router(config-if)#no service-policy input policerRouter(config-if)#service-policy input policer account user-defined -20Router(config-if)#commitRouter#sh run int hundredGigE 0/0/0/2interface HundredGigE0/0/0/2service-policy input policer account user-defined -20!

Positive Accounting Use Case

If QoS commitment includes Preamble, Frame Delimiter & Interframe Gap and has the following configuration:

service-policy input <foo> account user-defined +20

For QoS purposes, your router treats this packet as a packet of size = Actual Packet size + 20. Hence, the effective policing and shaping is reduced to match the downstream interface.

Negative Accounting Use Case

If QoS commitment to your router does not include VLAN header information, and has the following configuration:

service-policy input <foo> account user-defined -4

For QoS purposes, your router treats this packet as a packet of size = Actual Packet size – 4. Hence, the effective policing and shaping is increased to match the downstream interface.

Associated Commands

service-policy (overhead accounting)

Traffic Shaping

Traffic shaping allows you to control the traffic flow exiting an interface to match its transmission to the speed of the remote target interface and ensure that the traffic conforms to policies contracted for it. Traffic adhering to a particular profile can be shaped to meet downstream requirements, hence eliminating bottlenecks in topologies with data-rate mismatches.

Note

Traffic shaping is supported only in egress direction.

Configure Traffic Shaping

The traffic shaping performed on outgoing interfaces is done at the Layer 1 level and includes the Layer 1 header in the rate calculation.

Guidelines

Only egress traffic shaping is supported.
It is mandatory to configure all the eight traffic-class classes (including class-default) for the egress policies.
You can configure shape average command along with priority command.

Configuration Example

You have to accomplish the following to complete the traffic shaping configuration:

Creating or modifying a policy-map that can be attached to one or more interfaces
Specifying the traffic class whose policy has to be created or changed
Shaping the traffic to a specific bit rate and set peak burst size
Attaching the policy-map to an output interface

Router# configureRouter(config)#class-map c5 Router(config-cmap)#match traffic-class 5 Router(config-cmap)#commitRouter(config)# policy-map egress_policy1Router(config-pmap)# class c5Router(config-pmap-c)# shape average 40 percentpercent 50 1000Router(config-pmap-c# exitRouter(config-pmap)# exitRouter(config)# interface HundredGigE 0/1/0/0Router(config-if)# service-policy output egress_policy1Router(config-if)# commit

Running Configuration

class-map c5 match traffic-class 5 commitpolicy-map egress_policy1 class c5 shape average percent 40 ! class class-default ! end-policy-map!interface HundredGigE0/6/0/18 service-policy output egress_policy1!

class-map c5 match traffic-class 5 commitpolicy-map egress_policy1 class c5 shape average percent 50 1000 ! class class-default ! end-policy-map!interface HundredGigE0/6/0/18 service-policy output egress_policy1!

Verification

Router#  show qos interface hundredGigE 0/6/0/18 output NOTE:- Configured values are displayed within parenthesesInterface HundredGigE0/6/0/18 ifh 0x3000220 -- output policyNPU Id: 3Total number of classes: 2Interface Bandwidth: 100000000 kbpsVOQ Base: 11176VOQ Stats Handle: 0x88550ea0Accounting Type: Layer1 (Include Layer 1 encapsulation and above)------------------------------------------------------------------------------Level1 Class = c5Egressq Queue ID = 11177 (LP queue)Queue Max. BW. = 40329846 kbps (40 %)Queue Min. BW. = 0 kbps (default)Inverse Weight / Weight = 1 (BWR not configured)Guaranteed service rate = 40000000 kbpsTailDrop Threshold = 50069504 bytes / 10 ms (default)WRED not configured for this classLevel1 Class = class-defaultEgressq Queue ID = 11176 (Default LP queue)Queue Max. BW. = 101803495 kbps (default)Queue Min. BW. = 0 kbps (default)Inverse Weight / Weight = 1 (BWR not configured)Guaranteed service rate = 50000000 kbpsTailDrop Threshold = 62652416 bytes / 10 ms (default)WRED not configured for this class

Router#  ios#show qos interface tenGigE 0/0/0/0 output Wed Jul 10 14:18:37.783 UTCNOTE:- Configured values are displayed within parenthesesInterface TenGigE0/0/0/0 ifh 0x120 -- output policyNPU Id: 0Total number of classes: 1Interface Bandwidth: 10000000 kbpsPolicy Name: testVOQ Base: 1024Accounting Type: Layer1 (Include Layer 1 encapsulation and above)------------------------------------------------------------------------------Level1 Class = class-defaultEgressq Queue ID = 1024 (Default LP queue)Queue Max. BW. = 5031499 kbps (50 %)Queue Min. BW. = 0 kbps (default)Inverse Weight / Weight = 1 / (BWR not configured)Guaranteed service rate = 5000000 kbpsPeak burst = 2240 bytes (1000 bytes)TailDrop Threshold = 6258688 bytes / 10 ms (default)

Important Notes

Associated Commands

shape average

Traffic Policing

Traffic policing allows you to control the maximum rate of traffic sent or received on an interface and to partition a network into multiple priority levels or class of service (CoS).Traffic policing manages the maximum rate of traffic through a token bucket algorithm. The token bucket algorithm uses user-configured values to determine the maximum rate of traffic allowed on an interface at a given moment in time. The token bucket algorithm is affected by all traffic entering or leaving the interface (depending on where the traffic policy with traffic policing is configured) and is useful in managing network bandwidth in cases where several large packets are sent in the same traffic stream. By default, the configured bandwidth value takes into account the Layer 2 encapsulation that is applied to traffic leaving the interface.

Traffic policing also provides a certain amount of bandwidth management by allowing you to set the burst size (Bc) for the committed information rate (CIR). See, Committed Bursts and Excess Bursts.

The router supports the following traffic policing mode(s):

Single-Rate Two-Color (SR2C) in color-blind mode. See Single-Rate Policer.
Single-Rate Three-Color (SR3C) in color-blind mode.
Two-Rate Three-Color (2R3C) in color-blind mode. See Two-Rate Policer .

Restrictions

Traffic policing is supported only in ingress direction, and only color-blind mode is supported.
The policing rate accuracy may vary up to +/-2% from the configured policer value.
Ensure that you don’t configure a policer and match criteria for discard-class in the same class. Even though the configuration is allowed, the policer doesn’t work and allows all traffic without dropping packets.
Policer marking is not supported.
Policers are configured in the interface at the core level and “show qos int <>” value is displayed at the NPU level.

For policers configured in a bundle interface where bundle members are from the same NPU but different cores (NPU cores), each member sends the traffic up to the core level policer configuration, but “show qos int <>” displays the NPU level policer output.
Example:

For bundle interface with two 10GE members (same NPU, but one interface from core0, one interface from core1) 2R3C policer applied on bundle interface (1G confirm rate , 1G exceed rate – total 2G policer rate) will be shown on the “show qos int <>” output):

Interface in core0 – 500 Mbps confirm rate, 500 Mbps exceed rate

Interface in core1 – 500 Mbps confirm rate, 500 Mbps exceed rate

For traffic in one out of two interfaces, the policed rate will be 1Gbps. For traffic on two interfaces, policed rate will be 2Gbps.

Committed Bursts and Excess Bursts

Unlike a traffic shaper, a traffic policer does not buffer excess packets and transmit them later. Instead, the policer executes a “send or do not send” policy without buffering. Policing uses normal or committed burst (bc) values and excess burst values (be) to ensure that the router reaches the configured committed information rate (CIR). Policing decides if a packet conforms or exceeds the CIR based on the burst values you configure. Burst parameters are based on a generic buffering rule for routers, which recommends that you configure buffering to be equal to the round-trip time bit-rate to accommodate the outstanding TCP windows of all connections in times of congestion. During periods of congestion, proper configuration of the excess burst parameter enables the policer to drop packets less aggressively.

For more details, see Committed Bursts and Excess Bursts.

Single-Rate Policer

Single-Rate Two-Color Policer

A single-rate two-color (SR2C) policer provides one token bucket with two actions for each packet: a conform action and an exceed action.

Based on the committed information rate (CIR) value, the token bucket is updated at every refresh time interval. The Tc token bucket can contain up to the Bc value, which can be a certain number of bytes or a period of time. If a packet of size B is greater than the Tc token bucket, then the packet exceeds the CIR value and a default action is performed. If a packet of size B is less than the Tc token bucket, then the packet conforms and a different default action is performed.

Single-Rate Three-Color Policer

A single-rate three-color (SR3C) policer provides one token bucket with three actions for each packet: a conform action, an exceed action and a violate action. The packet is marked based on the CIR value and the two associated burst size - committed burst size (CBS) and excess burst size (EBS). If a packet does not exceed the CBS, it is marked as conformed packet. The packet is marked as exceeded if it exceeds CBS, but not the EBS. If it exceeds the EBS as well, it is marked as violate packet.

Configure Traffic Policing (Single-Rate Two-Color)

Traffic policing is often configured on interfaces at the edge of a network to limit the rate of traffic entering or leaving the network. The default conform action for single-rate two color policer is to transmit the packet and the default exceed action is to drop the packet. Users cannot modify these default actions.

Configuration Example

You have to accomplish the following to complete the traffic policing configuration:

Creating or modifying a policy-map that can be attached to one or more interfaces
Specifying the traffic class whose policy has to be created or changed
(Optional) Specifying the marking action
Specifying the policy rate for the traffic
Attaching the policy-map to an input interface

Router# configureRouter(config)# policy-map test-police-1Router(config-pmap)# class ipv6-6 Router(config-pmap-c)# set dscp cs2 (optional)Router(config-pmap-c)# set qos-group 7 (optional)Router(config-pmap-c)# police rate percent 20 burst 10000 bytesRouter(config-pmap-c-police)# exitRouter(config-pmap-c)# exitRouter(config-pmap)# exitRouter(config)# interface HundredGigE 0/6/0/18Router(config-if)# service-policy input test-police-1Router(config-if)# commit

Running Configuration

class-map match-any ipv6-6 match precedence 3 end-class-map!policy-map test-police-1 class ipv6-6 set dscp cs2 set qos-group 7 police rate percent 20 burst 10000 bytes ! ! class class-default ! end-policy-map!interface HundredGigE0/6/0/18 service-policy input test-police-1 service-policy output test-priority-1!

Verification

Router# show qos interface hundredGigE 0/6/0/18 inputNOTE:- Configured values are displayed within parenthesesInterface HundredGigE0/6/0/18 ifh 0x3000220 -- input policyNPU Id: 3Total number of classes: 2Interface Bandwidth: 100000000 kbpsAccounting Type: Layer1 (Include Layer 1 encapsulation and above)------------------------------------------------------------------------------Level1 Class = ipv6-6New dscp = 16New qos group = 7Policer Bucket ID = 0x102a0Policer Stats Handle = 0x8a8090c0Policer committed rate = 19980000 kbps (20 %)Policer conform burst = 9856 bytes (10000 bytes)Level1 Class = class-defaultDefault Policer Bucket ID = 0x102a1Default Policer Stats Handle = 0x8a808e78Policer not configured for this class

Associated Commands

police rate

Configure Traffic Policing (Single-Rate Three-Color)

The default conform action and exceed actions for single-rate three-color policer are to transmit the packet and the default violate action is to drop the packet. User cannot modify these default actions.

Configuration Example

You have to accomplish the following to complete the traffic policing configuration:

Running Configuration

class-map match-any ipv4-5 match precedence 3 end-class-map!policy-map test-police-1R3C class ipv4-5 set qos-group 7 police rate percent 20 burst 100000 bytes peak-burst 190000 bytes ! ! class class-default ! end-policy-map!interface HundredGigE0/6/0/18 service-policy input test-police-1R3C service-policy output test-priority-1!

Verification

Router# show qos interface hundredGigE 0/6/0/18 inputNOTE:- Configured values are displayed within parenthesesInterface HundredGigE0/6/0/18 ifh 0x3000220 -- input policyNPU Id: 3Total number of classes: 2Interface Bandwidth: 100000000 kbpsAccounting Type: Layer1 (Include Layer 1 encapsulation and above)------------------------------------------------------------------------------Level1 Class = ipv4-5New qos group = 2Policer Bucket ID = 0x102a1Policer Stats Handle = 0x8a8090c0Policer committed rate = 19980000 kbps (20 %)Policer conform burst = 99584 bytes (100000 bytes)Policer exceed burst = 188672 bytes (190000 bytes)Level1 Class = class-defaultDefault Policer Bucket ID = 0x102a1Default Policer Stats Handle = 0x8a808e78Policer not configured for this class

Associated Commands

police rate

Two-Rate Policer

The two-rate policer manages the maximum rate of traffic by using two token buckets: the committed token bucket and the peak token bucket. The dual-token bucket algorithm uses user-configured values to determine the maximum rate of traffic allowed on a queue at a given moment. In this way, the two-rate policer can meter traffic at two independent rates: the committed information rate (CIR) and the peak information rate (PIR).

The dual-token bucket algorithm provides users with three actions for each packet—a conform action, an exceed action, and an optional violate action. Traffic entering a queue with the two-rate policer configured is placed into one of these categories. The actions are pre-determined for each category. The default conform and exceed actions are to transmit the packet, and the default violate action is to drop the packet.

This figure shows how the two-rate policer marks a packet and assigns a corresponding action to the packet.

Also, see Two-Rate Policer Details.

The router supports Two-Rate Three-Color (2R3C) policer.

Configure Traffic Policing (Two-Rate Three-Color)

The default conform and exceed actions for two-rate three-color (2R3C) policer are to transmit the packet and the default violate action is to drop the packet. Users cannot modify these default actions.

Configuration Example

You have to accomplish the following to complete the two-rate three-color traffic policing configuration:

Creating or modifying a policy-map that can be attached to one or more interfaces
Specifying the traffic class whose policy has to be created or changed
Specifying the packet marking
Configuring two rate traffic policing
Attaching the policy-map to an input interface

Router# configureRouter(config)# policy-map policy1Router(config-pmap)# class ipv4-7Router(config-pmap-c)# set qos-group 4Router(config-pmap-c)# police rate percent 20 burst 100000 bytes peak-rate percent 50 peak-burst 200000 bytesRouter(config-pmap-c-police)# exitRouter(config-pmap-c)# exitRouter(config-pmap)# exitRouter(config)# interface HundredGigE 0/6/0/18Router(config-if)# service-policy input policy1Router(config-if)# commit

Running Configuration

policy-map policy1 class ipv4-7 set qos-group 4 police rate percent 20 burst 100000 bytes peak-rate percent 50 peak-burst 200000 bytes ! !interface HundredGigE 0/6/0/18 service-policy input policy1!

Verification

Router# show policy-map interface HundredGigE 0/6/0/18 NOTE:- Configured values are displayed within parenthesesInterface HundredGigE0/6/0/18 ifh 0x3000220 -- input policyNPU Id: 3Total number of classes: 8Interface Bandwidth: 100000000 kbpsAccounting Type: Layer1 (Include Layer 1 encapsulation and above)------------------------------------------------------------------------------Level1 Class = ipv4-4- - - - - -Level1 Class = ipv4-7New qos group = 4Policer Bucket ID = 0x102a3Policer Stats Handle = 0x8a8089e8Policer committed rate = 19980000 kbps (20 %)Policer peak rate = 49860000 kbps (50 %)Policer conform burst = 99584 bytes (100000 bytes)Policer exceed burst = 199168 bytes (200000 bytes)Level1 Class = class-defaultPolicer Bucket ID = 0x102a7Policer Stats Handle = 0x8a7c8510Policer committed rate = 29880000 kbps (30 %)Policer conform burst = 4194304 bytes (default)

Important Notes

A policer is programmed per NPU core on a bundle interface. So, all members on a bundle interface from the same core share the policer.

Associated Commands

police rate

Packets-Per-Second-Based Policer

Table 1. Feature History Table
Feature Name	Release Information	Feature Description
Packets-Per-Second-Based Policer	Release 7.4.1	Prior to this functionality, when configuring policers, the only available option for policer rates was bit-rate measured in units of bits per second (bps). With this release, you can configure policer rates in units of packets per second (pps) as well. pps-based policer is critical in fending off malicious attacks—when attackers target your specific resources with a vast amount of traffic that contain higher number of packets, but move at a slower packet rate. Protection from such attacks is possible because pps-based policers ensure that regardless of the packet size and rate, the policer only accepts a fixed number of packets per second. This functionality modifies the police rate command.

Policer rates so far—You used the police rate command to configure policers based on two parameters:
- bit-rates (default unit: bits per second or bps)
- Burst size (default unit: bytes)
packets-per-second (pps)-based policer—With this additional functionality, you can use the police rate command to configure policers in units of packets per second (pps). The pps configuration option is available as police rate <pps-value> pps. When you configure the pps option, ensure that you configure burst size in packets. (See Restrictions and guidelines.) Thus, the parameters for pps-based policer are:
- packets per second (pps)
- burst size (packets)

Why pps-based-policer—Networks face newer types of attacks, and these days malicious operators don’t necessarily employ aggressive tactics that involve overwhelming your bandwidth with large amount of traffic to cause distributed denial of service (DDoS). Now, some attackers go the ‘softer’ route, where they send smaller packet sizes at slower traffic rates. During such malicious network activity, a bandwidth-based policer can still aggregate up to many packets to be processed if the packet size is small. Attackers tend to use this behavior to bypass bandwidth-based policers to exploit vulnerabilities or try to hit performance limitations by increasing the packet rates.

Packets-per-second-based policers ensure that regardless of the packet size and traffic rate, the policer only accepts a fixed number of packets per second.

pps-based-policer support cheat-sheet—Here’s a quick look at some key support areas and their details for pps-based policer.


Support	Details
Classification and marking support	Same as that for bps-based-policer
Units	Equivalent kbps values display for QoS programming and statistics.
H-QoS	Support for parent and child policers
Bursts	Support for confirm burst (bc) and exceed burst (be) values in units of packets. The default value is in multiple of 128 bytes equivalent to 10 milliseconds.
Minimum pps value	For better granularity, recommended minimum value is 100 pps.

Restriction and guidelines
- This functionality is applicable only for ingress.
- When using a pps-based policer, ensure that you configure the burst-size value in number of packets as well. This is because a policer burst rate determines whether a specific number of packets out of contract would be subject to the next action (that is, exceed or violate).
- Within a QoS policy, configure the parent and child policies policers to either bps or pps. Else, the configuration displays an error when you try attaching the policy to an interface.
- For single-level policy maps: under the same policy map, you can configure one class map with bps-based policer and the other class map with a pps-based policer.
- For two-level hierarchical policy maps:
  - The parent and child-level policy maps must use the same unit-based policer. That is, both must have either pps-based or bps-based policers.
  - If you configure the child-level policy map with pps-based policer, ensure that the parent policy-map class default has a pps-based policer.
Configure pps-based policer—To configure pps-based policer, you must:
1. Configure a class map.
2. Create a service policy for the map and configure the pps values.
3. Attach the service policy to an interface.

/*Configure a class map*/Router(config)#class-map prec1  Router(config-cmap)#match precedence 1Router(config-cmap)# exitRouter(config)# commit/*Create a service policy map*/Router(config)# policy-map policy1Router(config-pmap)# class prec1Router(config-pmap-c)#police rate 1000 pps burst 300 packetsRouter(config-pmap-c-police)#exitRouter(config-pmap-c)#exitRouter(config-pmap)#exitRouter(config)# commit/*Attach the service policy to an interface*/Router#int hundredGigE 0/7/0/2Router(config-if)service-policy input policy1Router(config-if)#exitRouter(config)#commit

Running Configuration

class-map match-any prec1match precedence 1 end-class-map!policy-map policy1class prec1 police rate 1000 pps burst 300 packets ! ! class class-default! end-policy-map!

Verification

Router#show qos int hundredGigE 0/7/0/2 inputNOTE:- Configured values are displayed within parenthesesInterface HundredGigE0/7/0/2 ifh 0xe000088 -- input policyNPU Id: 0Total number of classes: 2Interface Bandwidth: 100000000 kbpsPolicy Name: policy1SPI Id: 0x0Accounting Type: Layer2 (Include Layer 2 encapsulation and above)------------------------------------------------------------------------------Level1 Class = prec1 Policer Bucket ID = 0x9Policer Stats Handle = 0x0Policer committed rate = 998 kbps (1000 packets/sec)Policer conform burst = 37632 bytes (300 packets) Level1 Class = class-default Default Policer Bucket ID = 0x8Default Policer Stats Handle = 0x0Policer not configured for this class

Associated Commands

police rate

Shared Policer

The classification of the incoming packet occurs only once. However, based on the different classification criteria, the shared policer feature allows sharing of the policer bucket amongst two or more classes in a QoS policy map . That is, the same token bucket is used for a traffic flow matching against any of the classes sharing the policer.

For example, let us say a policer of 10 Mbps is shared among two classes C1 and C2. This feature ensures that both C1 and C2 get traffic flow assigned on First Come First Serve (FCFS) basis. Also that, if C2 does not have any traffic, C1 uses all of the 10 Mbps for transmission.

This feature includes two components:

Policer Bucket Shared

Policer Bucket Referred

Policer Bucket Shared

The policer bucket shared feature defines and shares a policer bucket instance among multiple classes.

Here is a sample configuration that defines and shares policer bucket instance sp1 :

policy-map parent class long-distance police bucket shared sp1 rate 1 mbps

In this configuration, a policy-map for class long-distance traffic type is created to police at 1Mbps rate and the policer bucket is shared.

Policer Bucket Referred

The policer bucket referred feature refers a defined policer bucket instance. Shared policer is not supported across policy levels. This means for example, that parent and child policy cannot share a common bucket.

Here is a sample configuration that refers shared policer bucket instance sp1 :

policy-map voip-child class long-distance-voip police bucket referred sp1

In this configuration, a policy-map for class long-distance-voip traffic type is created and the shared policer bucket sp1 is referred.

Shared Policer Statistics

Currently, individual class statistics are not available as a default option for shared policer. You can access statistics in the following modes.

Aggregate Mode

In this mode the policer bucket is shared among two or more classes. However, statistics are not available for every individual class. You can view the aggregate statistics that combine the numbers for all the classes sharing the policer bucket.

Per-Class Mode

In this mode the policer bucket is shared among two or more classes, and you can also view individual class statistics. However, when this mode is active, the Policy-Based Tunnel Selection (PBTS) mechanism is disabled. To enable the per-class mode, you must configure the hw-module profile qos shared-policer-per-class-stats command.

Restrictions and Guidelines

The following restrictions and guidelines apply while configuring the shared policer feature.

When shared policer is enabled in per-class mode, Policy-Based Tunnel Selection (PBTS) mechanism is disabled. In other words, shared policer-per-class-mode and PBTS are mutually exclusive features.
Shared policer is not supported across policy levels. This means, for example, that parent and child policies cannot share a common policer bucket.
Shared policer is not supported in ingress peering mode.
Shared policer is supported within classes of the same policy. However, cross-policy bucket sharing is not supported.
There are no limitations on the number of classes that can share policer.
There are no changes in policer scale numbers in the aggregate and per-class modes.
All the existing policer types (1R2C, 1R3C and 2R3C) are supported.
You must reload the affected line card to enable the per-class-stats mode.

Configuring Shared Policer

To configure shared policer, you must:

Create a class map to be used for matching packets to the specified class.
Create a policy map to be used for matching packets to the specified class.
Specify a class name.
Define and share a policer bucket.
Specify a class name.
Refer a shared policer bucket.

RP/0/RSP0/CPU0:ios(config)#class-map match-any c1RP/0/RSP0/CPU0:ios(config-cmap)#match precedence 1RP/0/RSP0/CPU0:ios(config-cmap)#end-class-mapRP/0/RSP0/CPU0:ios(config)#class-map match-any c2RP/0/RSP0/CPU0:ios(config-cmap)#match precedence 2RP/0/RSP0/CPU0:ios(config-cmap)#end-class-mapRP/0/RSP0/CPU0:ios(config)#policy-map s-polRP/0/RSP0/CPU0:ios(config-pmap)#class c1RP/0/RSP0/CPU0:ios(config-pmap-c)#police bucket shared 1 rate 10 mbpsRP/0/RSP0/CPU0:ios(config-pmap-c-police)#exitRP/0/RSP0/CPU0:ios(config-pmap-c)#exitRP/0/RSP0/CPU0:ios(config-pmap)#class c2RP/0/RSP0/CPU0:ios(config-pmap-c)#police bucket referred 1RP/0/RSP0/CPU0:ios(config-pmap-c-police)#class class-defaultRP/0/RSP0/CPU0:ios(config-pmap-c)#exitRP/0/RSP0/CPU0:ios(config-pmap)#exitRP/0/RSP0/CPU0:ios(config)#interface HundredGigE 0/6/0/18RP/0/RSP0/CPU0:ios(config-if)#service-policy input s-polRP/0/RSP0/CPU0:ios(config-if)#commit

Running Configuration

class-map match-any c1 match precedence 1 end-class-mapclass-map match-any c2 match precedence 2 end-class-mappolicy-map s-pol class c1 police bucket shared 1 rate 10 mbps ! ! class c2 police bucket referred 1 ! ! class class-default ! end-policy-map!interface HundredGigE0/6/0/18 service-policy input s-pol!

Verification

In Aggregate Mode

RP/0/RP0/CPU0:ios#sh policy-map interface tenGigE 0/0/0/0 input Fri Nov 15 12:55:56.817 UTCTenGigE0/0/0/0 input: s-polClass c1 Classification statistics (packets/bytes) (rate - kbps) Matched : 1784530245/228419871360 8640780  Transmitted : 2067504/264640512 10011 Total Dropped : 1782462741/228155230848 8630769 Policing statistics (packets/bytes) (rate - kbps) Policed(conform) : 2067504/264640512 10011 Policed(exceed) : 1782462741/228155230848 8630769 Policed(violate) : 0/0 0 Policed and dropped : 1782462741/228155230848 Class c2 Classification statistics (packets/bytes) (rate - kbps) Matched : 0/0 0 Transmitted : 0/0 0 Total Dropped : 0/0 0 Policing statistics (packets/bytes) (rate - kbps) Policed(conform) : 0/0 0 Policed(exceed) : 0/0 0 Policed(violate) : 0/0 0 Policed and dropped : 0/0 Class class-default Classification statistics (packets/bytes) (rate - kbps) Matched : 0/0 0 Transmitted : 0/0 0 Total Dropped : 0/0 0Policy Bag Stats time: 1573822531986 [Local Time: 11/15/19 12:55:31.986]

In Per-Class Mode

RP/0/RP0/CPU0:ios#sh policy-map interface tenGigE 0/0/0/0 input Fri Nov 15 15:18:18.319 UTCTenGigE0/0/0/0 input: s-polClass c1 Classification statistics (packets/bytes) (rate - kbps) Matched : 1005369276/128687267328 4320337 Transmitted : 1163300/148902400 5013 Total Dropped : 1004205976/128538364928 4315324 Policing statistics (packets/bytes) (rate - kbps) Policed(conform) : 1163300/148902400 5013 Policed(exceed) : 1004205976/128538364928 4315324 Policed(violate) : 0/0 0 Policed and dropped : 1004205976/128538364928 Class c2 Classification statistics (packets/bytes) (rate - kbps) Matched : 1005341342/128683691776 4320335 Transmitted : 1166269/149282432 4997 Total Dropped : 1004175073/128534409344 4315338 Policing statistics (packets/bytes) (rate - kbps) Policed(conform) : 1166269/149282432 4997 Policed(exceed) : 1004175073/128534409344 4315338 Policed(violate) : 0/0 0 Policed and dropped : 1004175073/128534409344 Class class-default Classification statistics (packets/bytes) (rate - kbps) Matched : 49159/6292352 0 Transmitted : 49159/6292352 0 Total Dropped : 0/0 0Policy Bag Stats time: 1573831087338 [Local Time: 11/15/19 15:18:07.338]

Related Commands

hw-module profile qos shared-policer-per-class-stats

References for Modular QoS Congestion Management

Committed Bursts

The committed burst (bc) parameter of the police command implements the first, conforming (green) token bucket that the router uses to meter traffic. The bc parameter sets the size of this token bucket. Initially, the token bucket is full and the token count is equal to the committed burst size (CBS). Thereafter, the meter updates the token counts the number of times per second indicated by the committed information rate (CIR).

The following describes how the meter uses the conforming token bucket to send packets:

If sufficient tokens are in the conforming token bucket when a packet arrives, the meter marks the packet green and decrements the conforming token count by the number of bytes of the packet.
If there are insufficient tokens available in the conforming token bucket, the meter allows the traffic flow to borrow the tokens needed to send the packet. The meter checks the exceeding token bucket for the number of bytes of the packet. If the exceeding token bucket has a sufficient number of tokens available, the meter marks the packet.

Green and decrements the conforming token count down to the minimum value of 0.

Yellow, borrows the remaining tokens needed from the exceeding token bucket, and decrements the exceeding token count by the number of tokens borrowed down to the minimum value of 0.

If an insufficient number of tokens is available, the meter marks the packet red and does not decrement either of the conforming or exceeding token counts.

Note

When the meter marks a packet with a specific color, there must be a sufficient number of tokens of that color to accommodate the entire packet. Therefore, the volume of green packets is never smaller than the committed information rate (CIR) and committed burst size (CBS). Tokens of a given color are always used on packets of that color.

Excess Bursts

The excess burst (be) parameter of the police command implements the second, exceeding (yellow) token bucket that the router uses to meter traffic. The exceeding token bucket is initially full and the token count is equal to the excess burst size (EBS). Thereafter, the meter updates the token counts the number of times per second indicated by the committed information rate (CIR).

The following describes how the meter uses the exceeding token bucket to send packets:

When the first token bucket (the conforming bucket) meets the committed burst size (CBS), the meter allows the traffic flow to borrow the tokens needed from the exceeding token bucket. The meter marks the packet yellow and then decrements the exceeding token bucket by the number of bytes of the packet.
If the exceeding token bucket does not have the required tokens to borrow, the meter marks the packet red and does not decrement the conforming or the exceeding token bucket. Instead, the meter performs the exceed-action configured in the police command (for example, the policer drops the packets).

Two-Rate Policer Details

The committed token bucket can hold bytes up to the size of the committed burst (bc) before overflowing. This token bucket holds the tokens that determine whether a packet conforms to or exceeds the CIR as the following describes:

A traffic stream is conforming when the average number of bytes over time does not cause the committed token bucket to overflow. When this occurs, the token bucket algorithm marks the traffic stream green.
A traffic stream is exceeding when it causes the committed token bucket to overflow into the peak token bucket. When this occurs, the token bucket algorithm marks the traffic stream yellow. The peak token bucket is filled as long as the traffic exceeds the police rate.

The peak token bucket can hold bytes up to the size of the peak burst (be) before overflowing. This token bucket holds the tokens that determine whether a packet violates the PIR. A traffic stream is violating when it causes the peak token bucket to overflow. When this occurs, the token bucket algorithm marks the traffic stream red.

For example, if a data stream with a rate of 250 kbps arrives at the two-rate policer, and the CIR is 100kbps and the PIR is 200 kbps, the policer marks the packet in the following way:

100 kbps conforms to the rate
100 kbps exceeds the rate
50 kbps violates the rate

The router updates the tokens for both the committed and peak token buckets in the following way:

The router updates the committed token bucket at the CIR value each time a packet arrives at the interface. The committed token bucket can contain up to the committed burst (bc) value.
The router updates the peak token bucket at the PIR value each time a packet arrives at the interface. The peak token bucket can contain up to the peak burst (be) value.
When an arriving packet conforms to the CIR, the router takes the conform action on the packet and decrements both the committed and peak token buckets by the number of bytes of the packet.
When an arriving packet exceeds the CIR, the router takes the exceed action on the packet, decrements the committed token bucket by the number of bytes of the packet, and decrements the peak token bucket by the number of overflow bytes of the packet.
When an arriving packet exceeds the PIR, the router takes the violate action on the packet, but does not decrement the peak token bucket.

See Two-Rate Policer.

Modular QoS Configuration Guide for Cisco NCS 540 Series Routers, Cisco IOS XR Release 7.4.x - Configuring Modular QoS Congestion Management [Cisco Network Convergence System 540 Series Routers] (2024)

Congestion Management Overview

Class-based Weighted Fair Queueing

Bandwidth Remaining

Restrictions

Configuring Bandwidth Remaining

Configuration Example

Running Configuration

Verification

Related Topics

Associated Commands

Low-Latency Queuing with Strict Priority Queuing

Configuring Low Latency Queuing with Strict Priority queuing

Configuration Example

Running Configuration

Verification

Associated Commands

Overhead Accounting

Configuring for Overhead Accounting

Associated Commands

Traffic Shaping

Configure Traffic Shaping

Configuration Example

Running Configuration

Verification

Important Notes

Related Topics

Associated Commands

Traffic Policing

Restrictions

Committed Bursts and Excess Bursts

Single-Rate Policer

Single-Rate Two-Color Policer

Single-Rate Three-Color Policer

Configure Traffic Policing (Single-Rate Two-Color)

Configuration Example

Running Configuration

Verification

Related Topics

Associated Commands

Configure Traffic Policing (Single-Rate Three-Color)

Configuration Example

Running Configuration

Verification

Related Topics

Associated Commands

Two-Rate Policer

Configure Traffic Policing (Two-Rate Three-Color)

Configuration Example

Running Configuration

Verification

Important Notes

Related Topics

Associated Commands

Packets-Per-Second-Based Policer

Associated Commands

Shared Policer

Policer Bucket Shared

Policer Bucket Referred

Shared Policer Statistics

Aggregate Mode

Per-Class Mode

Restrictions and Guidelines

Configuring Shared Policer

Running Configuration

Verification

Related Commands

Committed Bursts

Excess Bursts

Two-Rate Policer Details

References