The traditional switches handle both Data path and Control path on its own Data path is usually related with Fast packet forwarding, whereas, Control path is associated with high level routing. OpenFlow separates a switch's data path and control path activities.
As OpenFlow makes control function independent of the hardware, it can have more attention on packet forwarding. The data-path functionality still resides on the switch, but a controller, typically a standard server, handles high-level routing decisions. By removing the control processing load from the switches, OpenFlow lets the switches focus on moving traffic as fast as possible.
OpenFlow introduces an open protocol to program the routing table in various switches and routers. A network manager can split traffic into Research traffic and Production traffic. Researchers can manipulate their own flows by controlling the routes their packets should obey and the processing they obtain. In this way, researchers can test newly designed routing protocols, addressing schemes, security models and even substitutes for IP. On the same network slice, the production traffic is segregated and processed in regular way.
An OpenFlow Switch
Most modern Ethernet switches include flow tables that describe how to move a packet efficiently from sender to destination. Each vendor's flow table is different, but researchers identified a set of functions such as- quality of service and traffic reporting, common to most high- end switches. OpenFlow standardizes this common set of features. An OpenFlow switch consists of three key parts-
- A Flow Table, which includes an action associated with each flow entry, to guide the switch how the flow is to be processed.
- A Secure Channel, that links the switch to a remote control process (called the controller), permitting commands and packet to be forwarded between a controller and the switch.
- The OpenFlow Protocol, which introduces an open and standard way for a remote controlling process (running on controller) to exchange information with a switch.
|Network of OpenFlow Enabled Switches|
A dedicated OpenFlow Switch is a dumb datapath constituent that dispatches packets between ports, as determined by a remote control process running on the controller. Each flow-entry defined by the remote control process, has a simple action related with it; the three primary ones (that all conventional OpenFlow switches must maintain) are:
- Forward a specific flow's packets to the specified port (or ports). This lets packets to be transmitted through the network. In most of the switches, this is anticipated to take place at net bit-rate.
- Encapsulate and forward a specific flow's packets to a controller. Packet is handed over to Secure Channel, where it is encapsulated and dispatched to a controller. Typically used for the very first packet in a new flow, in order that a controller can determine if the flow should be attached to the Flow Table. In some experiments, it can be used to redirect all packets to the remote controller for processing.
- Reject/Drop particular flow's packets. Useful in security related purposes, to restrain denial of service attacks, or to reduce bogus broadcast discovery traffic from end-hosts.
- As the data path and control path activities are divided, by allocating control path to centralized controller, performance of the network is found to be improved to much extent.
- It lets administrators deploy new features in existing network architecture.
- Centralized controller offers its administrators a unified viws of the entire netowork, which in turns enables better security and management in the network
- "OpenFlow will allow networks to evolve and improve more quickly than they can today.” - Mr. Urs Hoelzle, ONF.
- “OpenFlow will fit where you need less security”- Bill Seifert, chief technology officer of Avaya.
- “Yes, it could change the dynamics of networking but most users want switches and routers that just work. If OpenFlow can get to this level of functionality, simplify network architectures, and streamline network operations, it may [succeed].”- Jon Oltsik, an analyst for Enterprise Strategy Group.