The data plane includes the protocols and features that a
network device implements to forward traffic to its
destination as quickly as possible. Cisco Express
Forwarding (CEF) is a proprietary switching mechanism
that is part of the data plane. It was developed
specifically to increase the speed with which data traffic
is forwarded through network devices. You can read
more about the control and data planes in Chapter 17,
“Networking Components.”
Historically, the control plane and data plane were part
of the network device architecture, and they worked
together to determine the path that the data traffic
should take through the network and how to move this
traffic as fast as possible from its source to its
destination. As mentioned previously, software-defined
networking (SDN) suggests a different approach.
SDN separates the functionality of the control plane and
data plane in different devices, and several benefits
result. First, the cost of the resulting network should be
lower as not all network devices have to implement
expensive software and hardware features to
accommodate both a control plane and data plane. The
expensive intelligence from the control plane is
constrained to a few devices that become the brains of
the network, and the data plane is built with cheaper
devices that implement only fast forwarding. Second, the
convergence of this new network, which is the amount of
time it takes for all devices to agree on a consistent view
of the network, should be much lower than in the case of
the non-SDN architectures of the past. In networks of
similar sizes, the ones built with network devices that
implement both the control plane and the data plane in
their architecture take much longer to exchange all the
information needed to forward data traffic than do the
networks that implement separate control and data
plane functionality in their architecture. Depending on
the size of a network, this could mean waiting for