Policy Based Routing

By default, most cisco routers performs CEF. After the de-encapsulation of received packets on incoming interface, router can perform PBR before matching the packet’s destination with the CEF table, or reverse order depends on configuration.

Basic PBR configuration steps
Standard or Extended ACL: access-list 101 permit ip host
Route Map Configuration:
route-map name permit
  match ip address xxx        //standard or extended ACL
  set ip next-hop x.x.x.x / set interface xxxxx            //PBR firstly performed
  set ip default next-hop x.x.x.x / set default interface xxx     //normal routing processing first (default route ignored), then PBR performed.
  set ip precedence xxx / set ip tos xxx      //QoS marking, optional

Apply route map to interface:
interface Fastethernet 0/0
  ip address
  ip policy route-map name
NOTE: By default. PBR does not take effect on local generated packets. To allow PBR take effect on local originated packets, configure the ip local policy route-map name global command.

PBR can dynamically react to the network health level according to the current network performance evaluation of IP SLA tools。