Hierarchical QoS (H-QoS) allows you to specify QoS behavior at multiple policy levels, which provides a high degree of granularity in traffic management.

H-QoS is applied on the router interface using nested traffic policies. The first level of traffic policy, the parent traffic policy, is used for controlling the traffic at the main interface or sub-interface level. The second level of traffic policy, the child traffic policy, is used for more control over a specific traffic stream or class. The child traffic policy, is a previously defined traffic policy, that is referenced within the parent traffic policy using the service-policy command.

Two-level H-QoS is supported on both ingress and egress directions on all line cards and on physical or bundle main interfaces and sub-interfaces.

Three-level Hierarchical QoS (H-QoS) enables enforcement of class/service, group/ Ethernet Flow Point (EFP), and port level SLAs. You can apply regular two-level egress H-QoS policies on the sub-interfaces to achieve class and EFP SLAs at child and parent levels. In addition, you can apply a port shaper policy on the main interface to achieve an aggregated port level SLA in a 1+2 H-QoS or three-level H-QoS model.

An important point to note is that before Release 6.6.25 (where the three-level H-QoS capability was introduced), when you applied class-default shaper on a main interface, it was enforced only on the traffic going through the main interface. With three-level HQoS, a class default shaper that is applied on the main interface is considered as a port shaper and enforced on all traffic going out of that physical port. The advantage of three-level H-QoS is that the parent shaper on the sub-interfaces is allowed to oversubscribe, thus enabling best effort sharing of the aggregate port shaper at the third level.

The following restrictions are applicable while configuring H-QoS:

1. The parent traffic policy only supports the traffic class of type class-default.

2. The parent traffic policy only supports the class-action shape and no other queuing action can be configured in it.

3. While configuring on the router, it is mandatory that the priority class must have traffic shaper in the child traffic policy.

4. The sum of the bandwidth of the child policies must be less than the parent policy’s traffic shaper.

5. For congestion avoidance and management, the traffic shaper in the parent traffic policy calculates the queue limit and drop priority.

6. H-QoS profile and ingress peering profile don't work simultaneously. Hence, features requiring a peering profile also do not work with the H-QoS profile enabled.

7. PBTS feature does not work when the H-QoS profile is enabled. This is due to TCAM limitations.

8. A maximum of 896 bundle sub-interfaces are only supported in the system, even if there are no QoS policies applied. This is due to an internal LAG_ID resource consumption in HQoS profile mode for bundle sub-interfaces with or without QoS policies being applied.

9. A maximum of 4 priority levels are only supported in HQoS profile mode unlike the default mode where 7-priority levels are supported. The restriction also applies to physical and bundle main interface policies where 7-level priorities were previously used in non-H-QoS profile mode.

10. Bandwidth and Bandwidth remaining configurations are not supported simultaneously within the same policy-map. If a class has bandwidth (CIR), other classes must also have only bandwidth configuration. If a class-map has bandwidth remaining percent/ratio (EIR), other classes should also have only the bandwidth remaining configuration. Shaping is applied on any class.

11. In HQOS Mode, if multiple queues are configured with BRR and there is high congestion on the LP (Low Priority) queues then one queue with BRR gets more credits than rest of the LP queues. The deviation is proportional to the congestion in LP queues.

12. Priority classes must have rate limit configuration by using a Shaping configuration. The effective shaper value is taken as priority bandwidth reservation. Sum of priority bandwidth reservations across all sub-interfaces and main interfaces must not exceed the network interface (NIF) port speed. This is to avoid over-subscription of priority traffic across the network interface port.

    Rates of non-priority classes and parent shaping can be over-subscribed.

13. The granularity of bandwidth or bandwidth remaining ration (BRR) is 1:64 as compared to 1:4096 in non-hqos mode. So, there could be accuracy differences in bandwidth performance based on the values used.

14. Filtering for egress IPv4 and IPv6 multicast traffic is not supported if H-QoS is configured on the router.

The following restrictions are applicable while configuring three-level H-QoS:

• There is no support for bandwidth action at the EFP parent level. All EFP/sub-interface policies get a fair share of the port shaper.

• Three-level H-QoS does not apply to ingress policies or to egress marking policies.

• Executing clear qos counters on the main interface clears only the main interface policy statistics. Use the “all” option to clear all sub-interface statistics or alternately, clear the sub-interface policy statistics individually.

• Main interface policy statistics do not reflect the sub-interface packet / byte counters, although the port shaper is enforced on all logical ports for a given physical interface. The sub-interface policy-map statistics reflect the transmitted and dropped packet/byte count post-port shaper enforcement.

Before you configure H-QoS, you must enable the H-QoS profile on the router. After enabling H-QoS profile, reload the router, as shown in the following configuration.

admin
hw-module location all reload
Router# configure
Router(config)# hw-module profile qos hqos-enable
Router(config)# commit
Router# admin
sysadmin-vm:0_RP0# hw-module location all reload 

The steps that are involved in configuring hierarchical queuing are as follows:

1. Configure a class-map.

2. Configure a child traffic policy using the class-map that was configured in the previous step.

3. Configure a parent traffic policy and add the child traffic policy in it.

The parent traffic policy is the H-QoS traffic policy and it can be applied on physical or bundle main interfaces and sub-interfaces.

Router# configure
Router(config)# class-map match-any tc2
Router(config-cmap)# match traffic-class 1
Router(config-cmap)# end-class-map
Router(config)# commit

Router# configure
Router(config)# policy-map child
Router(config-pmap)# class tc2
Router(config-pmap-c)# shape average percent 20
Router(config-pmap-c)# exit
Router(config-pmap)# class class-default
Router(config-pmap-c)# shape average percent 1
Router(config-pmap)# end-policy-map
Router(config)# commit

Router# configure
Router(config)# policy-map parent
Router(config-pmap)# class class-default
Router(config-pmap-c)# service-policy child
Router(config-pmap-c)# shape average percent 50
Router(config-pmap)# end-policy-map
Router(config)# commit

/* Configuration of a Class-map */
class-map match-any tc2
 match traffic-class 1
 end-class-map
!
/* Configuration of a Child Traffic Policy */
policy-map child
 class tc2
  shape average percent 20
 !
 class class-default
  shape average percent 1
 !
 end-policy-map
!
/* Configuration of a Parent Traffic Policy */
policy-map parent
 class class-default
  service-policy child
  shape average percent 50
 !
 end-policy-map
!

Router# configure
Router(config)# Interface TenGigE 0/0/0/10
Router(config-int)# service-policy output parent
Router(config-int)# commit

Router# configure
Router(config)# Interface TenGigE 0/0/0/10.1
Router(config-int)# service-policy output parent
Router(config-int)# commit

RP/0/RP0/CPU0:ios#show qos interface ten0/0/0/10 output

NOTE:- Configured values are displayed within parentheses
Interface TenGigE0/0/0/10 ifh 0x1e0  -- output policy
NPU Id:                        0
Total number of classes:       3
Interface Bandwidth:           10000000 kbps
VOQ Base:                      1136
Accounting Type:               Layer1 (Include Layer 1 encapsulation and above)
------------------------------------------------------------------------------
Level1 Class                             =   class-default
Queue Max. BW.                           =   no max (50 %)
Queue Min. BW.                           =   0 kbps (default)
Inverse Weight / Weight                  =   0 / (BWR not configured)
   Level2 Class                             =   tc2
   Egressq Queue ID                         =   1138 (LP queue)
   Queue Max. BW.                           =   1020015 kbps (20 %)
   Queue Min. BW.                           =   0 kbps (default)
   Inverse Weight / Weight                  =   1 / (BWR not configured)
   Guaranteed service rate                  =   1000000 kbps
   TailDrop Threshold                       =   1253376 bytes / 10 ms (default)
   WRED not configured for this class
   Level2 Class                             =   class-default
   Egressq Queue ID                         =   1136 (Default LP queue)
   Queue Max. BW.                           =   50625 kbps (1 %)
   Queue Min. BW.                           =   0 kbps (default)
   Inverse Weight / Weight                  =   1 / (BWR not configured)
   Guaranteed service rate                  =   50000 kbps
   TailDrop Threshold                       =   62720 bytes / 10 ms (default)
   WRED not configured for this class

Router# show policy-map interface ten0/0/0/10 output

TenGigE0/0/0/10 output: parent
Class class-default
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :          2313578823/296138089344         8494665
    Transmitted         :           232805738/29799134464          854465
    Total Dropped       :          2080773085/266338954880         7640200
  Policy child Class tc2
    Classification statistics          (packets/bytes)     (rate - kbps)
      Matched             :          2313578823/296138089344         8494665
      Transmitted         :           232805738/29799134464          854465
      Total Dropped       :          2080773085/266338954880         7640200
    Queueing statistics
      Queue ID                             : 1138

      Taildropped(packets/bytes)           : 2080773085/266338954880
  Policy child Class class-default
    Classification statistics          (packets/bytes)     (rate - kbps)
      Matched             :                   0/0                    0
      Transmitted         :                   0/0                    0
      Total Dropped       :                   0/0                    0
    Queueing statistics
      Queue ID                             : 1136

      Taildropped(packets/bytes)           : 0/0

/*Hierarchical Policy Map Configuration*/
====================================================
Router# show running-config policy-map Hingress 
policy-map Hingress
 class class-default
  service-policy ingress
  police rate 5 gbps peak-rate 9 gbps 
  ! 
 ! 
 end-policy-map
! 
 /*Ingress Policy Map Configuration*/
=====================================
Router#show running-config policy-map ingress  
policy-map ingress
 class cos1
  set traffic-class 1
  police rate 5 gbps 
  ! 
 ! 
 class cos2
  set traffic-class 2
  police rate 5 gbps 
  ! 
 ! 
 class class-default
 ! 
 end-policy-map
! 
 /*Policy Map applied at TenGigE0/0/0/6.100 Interface*/
=======================================================
Router#show policy-map interface tenGigE 0/0/0/6.100 input 
 
TenGigE0/0/0/6.100 input: Hingress
 
Class class-default
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :           856717937/109659895936         6683676
    Transmitted         :           856717937/109659895936         6683676
    Total Dropped       :                   0/0                    0
  Policing statistics                (packets/bytes)     (rate - kbps) 
    Policed(conform)    :           856717937/109659895936         6683674
    Policed(exceed)     :                   0/0                    0
    Policed(violate)    :                   0/0                    0
    Policed and dropped :                   0/0                  
 
  Policy ingress Class cos1
    Classification statistics          (packets/bytes)     (rate - kbps)
      Matched             :           437826303/56041766784          3341838
      Transmitted         :           437826303/56041766784          3341838
      Total Dropped       :                   0/0                    0
    Policing statistics                (packets/bytes)     (rate - kbps) 
      Policed(conform)    :           437826303/56041766784          3341838
      Policed(exceed)     :                   0/0                    0
      Policed(violate)    :                   0/0                    0
      Policed and dropped :                   0/0                  
      Policed and dropped(parent policer)  : 0/0
 
  Policy ingress Class cos2
    Classification statistics          (packets/bytes)     (rate - kbps)
      Matched             :           418891634/53618129152          3341838
      Transmitted         :           418891634/53618129152          3341838
      Total Dropped       :                   0/0                    0
    Policing statistics                (packets/bytes)     (rate - kbps) 
      Policed(conform)    :           418891634/53618129152          3341838
      Policed(exceed)     :                   0/0                    0
      Policed(violate)    :                   0/0                    0
      Policed and dropped :                   0/0                  
      Policed and dropped(parent policer)  : 0/0
 
  Policy ingress Class class-default
    Classification statistics          (packets/bytes)     (rate - kbps)
      Matched             :                   0/0                    0
      Transmitted         :                   0/0                    0
      Total Dropped       :                   0/0                    0
Policy Bag Stats time: 0 
Policy Bag Stats time: 0 
 

Hierarchical QoS (H-QoS), while allowing for granular and multi-level management of traffic, does not allow for conform traffic from a child-level policy to a parent-level policy to get priority. This means that in case of excess traffic, the parent policer drops conform traffic packets from the child level as well.

The conform-aware hierarchical policy feature enables the parent-level policy to prioritize conform traffic from child-level policy over exceed and violate traffic.

Here is how it works: the child-level policer initially marks its packets as red, yellow, or green. Packets are marked based on the committed information rate (CIR) value and the two associated burst sizes - committed burst size (CBS) and excess burst size (EBS). If a packet does not exceed the CBS, it is marked as conformed packet (green). The packet is marked as exceeded if it exceeds CBS, but not the EBS (yellow). If it exceeds the EBS as well, it is marked as violate packet (red).

When the packets arrive at the parent level policer (which is color aware), the policer prioritizes the packets marked green over the packets marked yellow. After all the conform traffic (green) is transmitted and there are tokens available still, the yellow packets are transmitted next, instead of being marked as violate traffic (red).

To enable the conform-aware hierarchical policy feature run the command.

hw-module profile qos conform-aware-policer