- [Instructor] Everything a networking device does
can be broken into various planes
or areas of control.
The data plane is responsible for all
of the various parts of forwarding a message.
That covers reception, processing, and forwarding.
It's for this reason that the data plane is often referred
to as the forwarding plane.
Functions here include encrypting traffic,
network address translation,
filtering traffic with ACLs,
encapsulating and decapsulating as packets move up
and down the OSI model,
and adding or removing 802.1Q headers.
The control plane is where the decision-making happens.
This will be systems like routing protocols,
STP, IPv4 ARP, IPv6 neighbor discovery,
and switches learning MAC addresses.
In essence, its methods used to control the flow of data,
or how the device knows where to forward traffic.
Last, the management plane is everything associated
with management of the device.
This could be protocols like Telnet or SSH
that an engineer uses to make configuration changes.
This could also be interfaces
that automation products will use to connect in
and make adjustments.
In the vast majority of networks today,
the control plane is configured
in a distributed architecture.
The idea is that each device makes
its own forwarding decision based
on information it has at hand.
While routing protocols like OSPF share information
that help routers make better decisions,
ultimately they decide on their own.
There's also the concept of controller-based
or software-defined networking environments.
This is a centralized piece of software
that will replace the control plane
on the devices in the networking environment.
The individual devices will use the intelligence
of the centralized software plane
to decide how packets should be forwarded in the network.
It's for this reason
it's called a centralized control plane.
When the controller needs to reach out
to a piece of network equipment,
it does so via what's called the southbound interface.
The SBI is often an application programming interface
which is just a method for one program to talk to another.
An SBI could be something as simple as SSH, SNMP,
or OpenFlow or Cisco's OpFlex.
A northbound interface allows connections
from other applications that want to interact
with the controller to connect in.
The controller can gather information
about the network topology, lists of devices,
device capabilities,
even device interfaces and their states.
Although the nomenclature discussed may seem pretty foreign,
you will be surprised how frequently it comes up
in SDN and in controller-based discussions.