In the early days
of computing the idea of computer networking did not exist computers or
mainframes as they were known were large structures that took up entire floors
of buildings. To transfer any data from these mammoth machines you would need
to use a physical media such as magnetic tapes. As mainframes started to evolve
they needed new ways in which they could move data these new mediums presented
themselves in the form of remote terminal controllers or card readers that operated
as subservient devices known as peripherals directly controlled by the
mainframe. The first network connections that started to emerge at this point
in time were very simple point to point or point to multipoint links. This
limited the communications on a network to a small chain of physically
connected devices where the mainframe controlled what communications were sent.
Over time these
mainframe systems got smaller and more like the computer systems we are all
familiar with so as the technologies evolved a new way to connect all of these
separate systems to share communications without a mainframe arose. This need
for a new method of communication brought about the emergence of the local area
network (LAN) and along with it new technologies arrived such as IEEE 802.3 and
IEEE 802.5.
The LAN was a
shared media network and did not scale well so the solution that was devised to
solve this issue was the emergence of bridged networks. The idea of a bridged
network was to split the shared media network into separate segments to allow
for better aggregation of bandwidth as now not all of the devices would be
transmitting at the same time. The bridged network concept was later replaced
by switches that allowed for many more improvements such as VLAN implementation
and the spanning tree protocol that eliminated loops in a network just to
mention a few.
The final layer of
communication that was added to these networks was routing, many different
routing protocols were developed to allow networks to route traffic outside of
a LAN and across the internet. As switches and routers developed so did the
programmability of this hardware to deliver more secure and faster
communications. If you refer to Fig 01.1 below it illustrates how software
starts to play a role as the hardware becomes more efficient as it evolves over
the years.
Fig 01.1
Before the
emergence of Open Flow the protocol at the heart of SDN researchers were
examining new ways to evolve the networks of the future. The earliest work
recorded at programmable networks did not involve internet routers or switches
but in fact surrounded ATM switches. Fig 01.2 below denotes the earliest
technologies in existence that eventually led to the birth of Open Flow the
protocol and the emergence of SDN.
Project
|
Description
|
Open signaling
|
Separating the
forwarding and control planes in ATM switching (1999)
|
Active
networking
|
Separating
control and programmable switches (late 1990s)
|
DCAN
|
Separating the
forwarding and control planes in ATM switching (1997)
|
IP switching
|
Controlling
layer two switches as a layer three routing fabric (late 1990s)
|
MPLS
|
Separating
control software, establishing semi-static forwarding paths for flows in
traditional routers (late 1990’s)
|
RADIUS, COPS
|
Using admission control
to dynamically provision policy (2010)
|
Orchestration
|
Using SNMP and
CLI to help automate configuration of networking equipment (2008)
|
Virtualization
Manager
|
Using plug-ins
to perform network reconfiguration to support server virtualization (2011)
|
ForCES
|
Separating the
forwarding and control planes (2003)
|
4D
|
Locating control
plane intelligence in a centralized system(2005)
|
Ethane
|
Achieving
complete enterprise and network access and control using separate forwarding
and control planes and utilizing a centralized controller (2007)
|
Fig 01.2
The two
technologies to take note of from Fig 01.2 are Devolved Control of ATM Networks
(DCAN) and Open Signaling. As you can see from the above description DCAN and
Open Signaling both separated the forwarding and control planes in ATM switches
and gave the control to an external device very similar to the controller
function in SDN networks. This technology never fully gained the trust of IT
Administrators and as a result never became a mainstream technology. The rest of the technologies in Fig 01.2 all
played a part in the steps required to get to where we are today with SDN. It wasn’t however until the arrival of Open
Flow that SDN was actually born the year was 2008 and researchers along with
vendors had started to play with the idea of Open Flow. Open Flow was designed
to allow researchers to experiment and innovate with protocols in everyday
network. This concept was to become a defining change how the industry approached
networking. It wasn’t until 2011 that SDN actually started to make an impact on
the networking industry as many big named vendors such as Cisco started to
implement the Open Flow specification into their products. The Open Flow
specification indicates the protocol to be used between the SDN controller and
the switch it also specifies the behavior that is expected from the switch.
If we look at this
specification in more detail we can break it down into a number of bullet
points the basic operation of an Open Flow solution is.
·
The controller populates the
flow table entries on the switches
·
The switch examines incoming
packets when it identifies a matching flow it carries out the action associated
with the flow
·
If the switch cannot find a
matching flow it forwards the packet to the controller and waits for further
instructions on how to deal with the packet
·
The controller will update the
switch with new flow entries as new patterns are identified this allows the
switch to deal with these packets locally.
The best resource for
information on the Open Flow standard is the Open Networking Foundation (ONF) established
in 2011 by Deutsche Telekom, Facebook, Google, Microsoft, Version and Yahoo. One
of the most powerful aspects of Open Flow is the fact that it is open meaning
researchers can contribute to new methods of network management, operation and
control unlike the closed shop model of networking that exists in today’s network’s
and as a result has lead to stifled innovation.
One major advantage
of having an open source platform for networking is security; it is widely known
that open source software tends to be a lot more secure than off the shelf distributions.
This is due to the fact that open source can be peer reviewed by anyone interested
in the field leading to faster discovery and patching of security issues and weakness
before a product is introduced to a working environment. This is the type of innovation
that networking has been lacking but with the introduction of SDN this is all starting
to change.
