In any PfR environment there will always be a single device that manages all aspects of PfR operations. The Msater Controller or MC will monitor outbound traffic flows and apply policies to optimize routing for specific subnets and exit links. While the MC is making all of the routing decisions in the network, its important to understand that this device does not have to be in-line with the traffic flows it’s controlling. It just needs to be reachable by other participating slave routers. The MC can support up to 20 managed exit interfaces.
The MC and border router can be run on a single device, this is used primarily in SOHO environments where there are a limited number of routing devices needed.
The MC in branch office networks resides coreside on one of the multiple border routers.
The MC can also be standalone, sitting in a datacenter for the customer, border routers will communicate to it over a private VPN to exchange traffic data and routing decisions.