QoS for Bridge-Group Virtual Interfaces

Integrated Routing and Bridging (IRB) provides the ability to route between a bridge group and a routed domain with the help of Bridge-Group Virtual Interface (BVI).

The BVI is a virtual interface within the router that acts like a normal routed interface that does not support bridging, but represents the comparable bridge group to routed interfaces within the router. The interface number of the BVI is the number of the bridge group that the virtual interface represents. The number is the link between the BVI and the bridge group.

For more information on IRB/ BVI, please refer the Interface and Hardware Component Configuration Guide for Cisco NCS 540 Series Routers

Information on Qos on BVI

A BVI integrates Layer2 domain with Layer3 domain by creating a virtual interface in between them. The traffic flow supported for QoS is from the bridged to routed interface.

  • A BVI can have bridge domain members from different linecards or NPU or Core.

  • A BVI service-policy is applied on all linecards and within each linecard it is replicated per NPU. If any policers are configured in the qos policy map is applied to the BVI interface, then the policer is configured on each core of the NPU, and is shared among all the interfaces on that NPU core.

Restrictions on BVI

  • Egress QoS on BVI is not supported for Layer2 flows for routed to bridge domain traffic.

  • QoS on BVI is not supported for:

    • Queuing (priority, bandwidth, bandwidth remaining, sShaping, queue-limit, random-detect)

    • Shared policy instance

    • Overhead accounting

    • Percentage policer at the parent level

  • Conditional EXP marking is only supported for Layer3 VPN when BVI is the AC interface or the packets have destination MAC address as BVI interface.

    Conditional EXP marking is not supported for EVPN (Layer2 traffic – non-BVI destination MAC traffic).

  • Inheriting a policy map must be from either from a BVI interface or main interface.

    The policy map on a bridge domain sub-interface is inherited by the main interface and BVI interface. If the policy is applied on both the interfaces, then the policy is inherited on the last applied interface. This configuration is not supported and should be avoided to undesired or unknown behavior.

  • A policy on a BVI interface should be applied after the BVI is added to the bridge domain as a routed interface. If the policy is applied before, then the policy has no effect.

  • The show QoS interface command is not supported for the BVI interface.

Classification and Marking

The following features are supported:

  • Classification

  • Policing (level 1 and level 2)

  • Ingress marking

Table 1. Classification and Marking

Classification

Marking

Direction

Comment

Qos-group

No

Yes

Ingress

Used for Egress marking policy

Discard-class

No

Yes

Ingress

Used for VOQ selection and Egress queuing policy

Precedence

Yes

Yes

Ingress

DSCP

Yes

Yes

Ingress

Vlan

No

No

CoS

Yes

No

Ingress

Only for Layer2 flows (bridge member).

Dei

Yes

No

Ingress

Only for Layer2 flows (bridge member).

EXP

No

Yes

Ingress

Configuring QoS on BVI 


Router# show running-config interface bvI 1

interface BVI1
 service-policy input bvi-ingress
 ipv4 address 1.1.1.1 255.255.255.0
!

Router# show running-config policy-map bvi-ingress 

policy-map bvi-ingress
 class prec1
  set traffic-class 1
  set mpls experimental imposition 3
  police rate 100 mbps 
  ! 
 ! 
 class dscp_af22
  set traffic-class 2
  set mpls experimental imposition 4
  police rate 200 mbps 
  ! 
 ! 
 class class-default
 ! 
 end-policy-map
! 

Router# show qos interface bvI 1 input 

NOTE:- Configured values are displayed within parentheses
Interface BVI1 ifh 0x800464c  -- input policy
NPU Id:                        0
Total number of classes:       3
Interface Bandwidth:           104857600 kbps
Policy Name:                   bvi-ingress
SPI Id:                        0x0
Accounting Type:               Layer1 (Include Layer 1 encapsulation and above)
------------------------------------------------------------------------------
Level1 Class                             =   prec1
New traffic class                        =   1
New imposition exp                       =   3

Policer Bucket ID                        =   0x6
Policer Stats Handle                     =   0x0
Policer committed rate                   =   99844 kbps (100 mbits/sec)
Policer conform burst                    =   124672 bytes (default)

Level1 Class                             =   dscp_af22
New traffic class                        =   2
New imposition exp                       =   4

Policer Bucket ID                        =   0x5
Policer Stats Handle                     =   0x0
Policer committed rate                   =   199688 kbps (200 mbits/sec)
Policer conform burst                    =   249472 bytes (default)

Level1 Class                             =   class-default

Default Policer Bucket ID                =   0x4
Default Policer Stats Handle             =   0x0
Policer not configured for this class

Verifying QoS on BVI

Use the show policy-map interface input command to collect statistics from all linecards. 

Router# show policy-map interface bvI 1 input                   

BVI1 input: bvi-ingress

Class prec1
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :                   0/0                    0
    Transmitted         :                   0/0                    0
    Total Dropped       :                   0/0                    0
Class dscp_af22
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :                   0/0                    0
    Transmitted         :                   0/0                    0
    Total Dropped       :                   0/0                    0
Class class-default
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :                   0/0                    0
    Transmitted         :                   0/0                    0
    Total Dropped       :                   0/0                    0