Under normal operating circumstances, which of the following planes sends the least amount of traffic to the route processor of a Cisco router? (Select the best answer.)
- the data plane
- the control plane
- the services plane
- the management plane
Under normal operating circumstances, the data plane sends the least amount of traffic to the route processor of a Cisco router. The data plane is one of the four logical components that collectively define a router? the remaining components are the control plane, the management plane, and the services plane. Traffic from the data plane consists primarily of usergenerated traffic that is forwarded from one interface to another on a router. This type of traffic is also referred to as transit traffic.
Cisco routers can use several different forwarding mechanisms to process transit traffic. The slowest of these Layer 3 switching mechanisms is process switching, which uses the router’s CPU, which is also known as the route processor, to determine the next hop and forwarding interface associated with the destination IP address of a received packet. Once a router has a corresponding entry in its route cache or Cisco Express Forwarding (CEF) table, all subsequent packets matching that entry’s destination can be fastswitched to the appropriate interface without involving the CPU. The fastswitching mechanism can handle significantly higher throughput than the processswitching mechanism because most, if not all, of its functions can be implemented directly by the switching fabric of the router.
By contrast, nearly all traffic from the control plane and management plane is handled by the router processor on a Cisco router. Control plane traffic typically consists of packets that are intended to create or perform network operations on a router, such as packets from dynamic routing protocols or Address Resolution Protocol (ARP) packets, whereas management plane traffic consists of packets used to administer the router, such as Telnet or Secure Shell (SSH) session traffic. These packets cannot be handled by Cisco’s normal fastpath switching mechanisms, because they require special handling by the router’s CPU.
Traffic from the services plane is a special kind of data plane traffic that requires some degree of processing by the router CPU before it can be placed into the fastswitching path. For example, Generic Routing Encapsulation (GRE) encapsulation or Quality of Service (QoS) processing might need to be applied to traffic before it is placed into the fast path. Although not all services plane traffic must be processed by the CPU, considerably more services plane traffic involves the CPU than data plane traffic does.