SOFTWARE DEFINED NETWORKING
Software defined networking is the latest revolution
in networking innovations. All components
of the networking industry, including network
equipment vendors, Internet service providers,
cloud service providers, and users, are working
on or looking forward to various aspects of SDN.
This section provides an overview of SDN.
SDN consists of four innovations:
1. Separation of the control and data planes
2. Centralization of the control plane
3. Programmability of the control plane
4. Standardization of application programming
interfaces (APIs)
Each of these innovations is explained briefly
below.
SEPARATION OF CONTROL AND DATA PLANE
Networking protocols are often arranged in
three planes: data, control, and management.
The data plane consists of all the messages that
are generated by the users. To transport these
messages, the network needs to do some housekeeping
work, such as finding the shortest path
using L3 routing protocols such as Open Shortest
Path First (OSPF) or L2 forwarding protocols
such as Spanning Tree. The messages used
for this purpose are called control messages and
are essential for network operation. In addition,
the network manager may want to keep track of
traffic statistics and the state of various networking
equipment. This is done via network management.
Management, although important, is
different from control in that it is optional and is
often not done for small networks such as home
networks.
One of the key innovations of SDN is that
the control should be separated from the data
plane. The data plane consists of forwarding the
packets using the forwarding tables prepared by
the control plane. The control logic is separated
and implemented in a controller that prepares
the forwarding table. The switches implement
data plane (forwarding) logic that is greatly simplified.
This reduces the complexity and cost of
the switches significantly.