Even though the control plane isn’t effective at forwarding, can it still used to route?
Under special circumstances Yes! such as control plane policing(QoS). A better example and my favourite is PBR. Let’s dive into a CCIE EL topic- PBR(Policy Based Routing)
All forwarding is done by data plane however, under some circumstances, the control plane can use its mechanism to determine the egress interface of a packet.
From the above diagram using OSPF all traffic will take the shortest path. Everything will be forwarded to data plane FIB. All traffic will from R1 will flow towards R2. Simply because of bandwidth is shortest to R2(gigabit links)
The server admin, want a dedicated traffic path to server behind R4. At the moment The server admin’s traffic will flow with all other traffic through R2, Simply because a router has one routing table in the CP. In this situation we can set PBR policy map to manipulate the control plane and send all server admins traffic through R3 even though it’s not the shortest path!
Subsequently by manipulating the control plane it will look like below
Stay tuned for the Lab on Policy Based Routing in part 2!
Until then ….see you on the other side
Network Automator 