Juniper_QPPB

Using destination-class to achieve the QoS Policy Propagation via BGP (QPPB) on M-series routers

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SUMMARY:

In QoS design, BGP community might be used to represent service class; this is called QoS Policy Propagation via BGP (QPPB) by other vendors.   For JUNOS on M-series, the destination-class (DCU) does the similar function of QPPB.

SOLUTION:

JUNOS has two different features to achieve the QPPB on M-series.  

• • classification-override which can only change traffic forwarding class based on BGP community

  • destination-class. (DCU).  The DCU is using normal JUNOS firewall to do action on the matched traffic.  Besides the forwarding class changing, DCU can change the loss-priority (PLP) and do policing.

Configuration example:

The remote router is sending a prefix with community 100:1000 which indicates low priority traffic's destination.  The below configuration will forward the traffic designated to this prefix into queue 1 and mark the loss-priority to be high.

• 1. On the local router, define a policy to match the prefix with community 100:1000 and tag them to be "dcu-1". Then apply the policy to forwarding table. 

  2. routing-options {

  3.     forwarding-table {

  4.         export set-destination-class;

  5.     }

  6. }

  7. policy-options {

  8.     policy-statement set-destination-class {

  9.         term 1 {

  10.             from community low-priority-traffic;

  11.             then destination-class dcu-1;

  12.         }

  13.         term 2 {

  14.             then accept;

  15.         }

  16.     }

  17.     community low-priority-traffic members 100:1000;

  18. }

  19. Define CoS configuration.

  20. class-of-service {

  21.     forwarding-classes {

  22.         queue 0 best-effort;

  23.         queue 1 low-priority;

  24.         queue 3 network-control;

  25.     }

  26.     interfaces {

  27.         so-0/1/0 {

  28.             scheduler-map juniper;

  29.         }

  30.     }

  31.     scheduler-maps {

  32.         juniper {

  33.             forwarding-class best-effort scheduler 95-95-high;

  34.             forwarding-class low-priority scheduler 0-0-low;

  35.             forwarding-class network-control scheduler 5-5-stright-high;

  36.         }

  37.     }

  38.     schedulers {

  39.         5-5-stright-high {

  40.             buffer-size percent 5;

  41.             priority strict-high;

  42.         }

  43.         0-0-low {

  44.             buffer-size percent 0;

  45.             priority low;

  46.         }

  47.         95-95-high {

  48.             transmit-rate percent 95;

  49.             buffer-size percent 95;

  50.             priority high;

  51.         }

  52.     }

  53. }

  54. Define the firewall filter to match traffic tagged with destination class dcu-1 and an action with forwarding-class and loss-priority changing. Then apply the filter to the interface's outbound direction.

  55. interfaces {

  56.     so-0/1/0 {

  57.         unit 0 {

  58.             family inet {

  59.                 filter {

  60.                     output differentiate-forwarding-class;

  61.                 }

  62.                 address 1.1.1.1/30;

  63.             }

  64.         }

  65.     }

  66. }

  67. firewall {

  68.     filter differentiate-forwarding-class {

  69.         term low-priority-traffic {

  70.             from {

  71.                 destination-class dcu-1;

  72.             }

  73.             then {

  74.                 loss-priority high;

  75.                 forwarding-class low-priority;

  76.             }

  77.         }

  78.         term others {

  79.             then accept;

  80.         }

  81.     }

  82. }