What is the SDN?
SDN is an acronym for software defined network, the software-defined network.
Why SDN? What is SDN able to do the traditional networks can not do?
Switch on the SDN is essentially nothing but the traditional switch chip packaging about it, what forwarding behavior is not supported by the traditional switch? (Forwarding plane)
traditional switches with network management software or command line to manage, SDN switch is simply replaced by controller controller to manage it, what is the essential difference? (Control plane)
In fact, SDN and traditional networks are essentially different, traditional network forwarding behavior is controlled by the protocol, reflecting the wishes of the administrator, but:
1. individually controlled by the device is pure distributed control;
2. the control plane with the forwarding plane in the same equipment;
3. administrators can not directly control the forwarding behavior, can only configure the network protocol, the protocol itself to influence the forwards;
4. impact of network protocol for forwarding behavior is fixed, such as routing agreement can only rely on the destination IP address forwarding, MPLS protocol can only rely on label forwarding packets and can only be modified fixed pattern, such as changing the Mac address, vlantag, TTL, DSCP, powerless to change anything else.
SDN requires centralized control, (even if there is distributed, that is a centralized re-release), forwarding and control separation requirements. So that administrators can directly manipulate the forwarding behavior of the device, without going through a variety of network protocols, but directly to control the forwarding behavior by the application.
Note that here say the use of network protocols, not to say SDN eliminate the network protocol, but these protocols run on the controller.
Above control forwarding behavior it is very straightforward, without any agreement effects, such as by not forwarding destination IP address, destination IP address but would like to see added to the source IP addresses and forwards when directly modify the destination IP addresses of packets and so on.
Summary, plainly, traditional network equipment, although there are plenty of software involved, but not the administrator to write, and can not reflect the will of their own, but fixed equipment manufacturers, naturally, not protocol (software) define a network; and SDN software is entirely designed for administrators, forwarding behavior in any network planning software, the administrator to fully define the entire network through the software, so-called software defined network.
SDN software to reach what is?
In fact, a variety of applications application, such as video surveillance management software, which relies on a graphical interface software to control the device, provision of data to be sent to the server, take that path; another example firewall software control, by graphical operating interface control device, in line with what conditions the packet can be released, sent to the monitoring server-depth analysis.
These are not forced to operate the software only works, it can be pre-configured policies dynamically according to the network administrator to configure the device. For example, to a certain time, so that the timing device to enable a feature; as well as more complex applications, such as automatic deployment of network virtualization software, automated flow test traffic engineering, route planning software.
These software have a common characteristic: not dependent on any routing exchange protocol, but the user's own custom designed, can be used to achieve automatic control, fully reflect the will of the user.
SDN is not a specific technology, but a framework for network design concept, SDN framework network, a control plane and forwarding plane must be isolated, the forwarding plane this angle, is to protocol-independent, and is software that can fully reflect the will of the administrator, the administrator software used to control the forwarding behavior, drive the entire network traffic.
Some SDN subtext:
the hardware forwarding plane configuration of standardized interfaces, if you want to achieve with the software controlling the forwarding behavior, you should try not to rely on specific hardware, or software can not be universal.
Centralized control, since it is a software-defined network, the network devices are in need of a unified control software.
Standardized hardware forwarding plane, not configuration interface, but the internal logic to achieve, otherwise it will create differences in different standards organizations and companies in behavior.
Summary: SDN characteristic properties:
1. The separation of control plane and forwarding plane
2. Open programmable interface
3. The centralized control network
4. The network traffic control automation applications
first two SDN core properties, provided that they meet the two point, can be considered SDN architecture.
Note that this does not include standardized hardware programming interface, but have to open technology, and hardware programming interface standard has been a good direction to pursue openflow the deliberate, requires not only programming interface standardization, also called internal hardware forwarding behavior should be standardized. This is the difference between traditional standards organization ONF equipment manufacturers and OpenFlow lies.
SDN what not?
SDN is the SDN, nor any other technology.
Is not equal to SDN OpenFlow, is not equal to the network virtualization network virtualization, virtual network function is not equal to NFV, network function virtualization, the cloud is not equal to or more large data and data center network.
SDN does not necessarily mean using OpenFlow, the network virtualization / cloud computing / big data / data center network does not necessarily need to use SDN.
SDN is not network protocol, not a network management tool, just the idea kind of network architecture, planning the various parts of the network component (software and hardware, forwarding and control planes) and the interaction between each other.
