10-5 QoS Policy Propagation via BGP

• Packets can be classified through the use of a BGP community list, an autonomous system (AS) path list, or a standard IP access list.

• Traffic coming in to a network can be prioritized according to BGP attributes.

• QoS policies can be distributed to remote BGP peers in a network.

NOTE

CEF must be enabled on the router. BGP should also be configured in advance. See Section 7-6 for more information about BGP configuration.

Configuration

1. Define a method for policy propagation.

   1. Define a community list:

       (global)  ip community-list   community-list-number  {  permit   deny  }  community-number  

      Permit the community numbers that you want to classify.

   2. Define an AS path list:

       (global)  ip as-path access-list   path-list-number  {  permit   deny  }  as-reg-expression  

      Permit the matching AS paths that you want to classify.

   3. Define an access list:

       (global)  access-list   acc-list-number  {  permit   deny  }  source  

      Use a standard IP access list to permit the source addresses you want to classify.

2. Use a route map to match and set the IP Precedence.

   1. Define the route map:

       (global)  route-map   route-map-name  [  permit   deny  ] [  sequence  ] 

   2. Specify a list type for matching:

       (route-map)  match community-list   community-list-number  [  exact  ] 

      -OR-

       (route-map)  match as-path   path-list-number  

      -OR-

       (route-map)  match ip address   acc-list-number  

      The route map can match against a list you configured in Step 1: a community list, a BGP AS path list, or a standard IP access list.

3. Set the IP Precedence:

    (route-map)  set ip precedence  [  number   name  ] 

   The IP Precedence number or name can be given, to be set on matching packets.

4. Configure BGP to use the route map:

    (global)  router bgp   as-number  (bgp)  table-map   route-map-name  

5. Enable IP Precedence propagation on an interface:

    (interface)  bgp-policy ip-prec-map  

   Packets are classified by using the IP Precedence values.

QoS Policy Propagation via BGP Example

A router is configured with BGP in AS 22. IP Precedence flash is assigned to traffic with a source network of 128.77.69.0, and critical is assigned to routes with an AS path going through AS 101. All other traffic receives a Precedence value of routine.

  access-list 10 permit 128.77.69.0   ip as-path access-list 1 permit _101_   route-map mypolicies permit 10   match ip address 10   set ip precedence flash   route-map mypolicies permit 20   match as-path 1   set ip precedence critical   route-map mypolicies permit 30   set ip precedence routine   router bgp 22   neighbor 17.7.1.45 remote-as 50   table-map precedence-map   interface serial 0/1   bgp policy ip-prec-map