Reprinted from :

I think it's very suitable for SDN An entry-level conceptual understanding of , For the time being copy once , After further research , Then slowly add your own things .

1. What is the SDN

1) Why a new network architecture is needed , such as SDN?

In the traditional architecture , Switches and routers have to be operating 6000 A distributed protocol is used to implement the intelligence of the whole network . That means , Even if only one network element adds a new protocol , It also requires all other network elements to make corresponding structural changes . in fact , It often takes years to add a new protocol to the network , To finally complete the process from standardization to actual deployment .

SDN Make the network programmable , This makes the network more flexible in meeting the needs of users .

2)SDN What's the architecture of ?

SDN Separate the control function from the network switching equipment , Move it into a logically independent control environment ------ In network control system . The system can run on a common server , Any user can , Direct control function programming . Control functions are no longer limited to routers . The control system provides a set of API, The user can go through API Monitor the control system 、 management 、 maintain .

Supplement the basic concepts :

(1) Control plane : It's the element in the data network that makes forwarding decisions , Such as routing protocol , The routing strategy and the software and hardware resources for running these protocols on the network equipment .

The decision includes forwarding to that path , Whether to enable multiple paths to forward the same data stream, etc .

(2) The data plane is part of the forwarding decision for the specified control plane , Including data encapsulation and de encapsulation technology , Tell and forward chip of network protocol, etc .

2. SDN The benefits of

1) SDN Speed up the introduction of new business . Network operators can deploy related functions through controllable software , Instead of waiting for a device provider to add a solution to a proprietary device as before ;

2)SDN It reduces the operation cost of the network . Eliminates application and network specific details ---- such as , Port and IP relation , No need to spend time and money to configure network devices ;

3)SDN Help with network virtualization . For a long time, manual configuration through the command line interface , It's been blocking the Internet from moving towards virtualization .

4) SDN Let the Internet and all IT The system is more business oriented . Add software modules to add SDN function .

5) Simplify network deployment .

3. openflow stay SDN What's the role of ?

openflow yes SDN One of the three key elements of .

SDN The first key element of this is the separation of forwarding and control , This makes it easier for network switches to forward , Efficient ; meanwhile , Control becomes a relatively centralized logic function in network operating system .

The second key is openflow agreement , It sends forwarding to the switch , The switch forwards the message accordingly . This is totally different from the traditional network . In the traditional network , Switches and routers need to decide the forwarding path of messages by themselves , The cost of taking photos increases , Performance degradation .

The third key element is consistency , System wide network operating system programmable interface , It enables networks to be truly programmable or software defined networks .

openflow Agreements are not necessary , There are other ways , Just transfer the flow meter information to the switch .

4. Network devices work in stream based mode

In order to ensure the efficiency of forwarding data , Most network devices are based on stream forwarding . With brand new FTP For example :

(1) FTP When the first data table of the service arrives at the switch, the routing protocol or layer 2 routing protocol calculates the out port of the packet , And store the results in the TCAM( Ternary content addressable memory , That is to say, it records where you can go from there ).

(2) When the data plane of the switch receives a packet , It sends the address information of the packet ( That is to say “ Where are from ” Information ) And TCAM comparison , If you can find all the table entries , According to the query results ( That is to say “ Where are you going? ” Information ) Forward .

Be careful : In the whole process , The switch control plane only needs to calculate the routing of the first packet of each flow ( What the switch control plane does ), And write the results to TCAM, Subsequent decisions are made by looking up TCAM. The advantage is that the forwarding efficiency is greatly improved .

5. SDN Controller Working mode of

SDN It's based on flow Work ,SDN Controller The main work is to set up and manage the maintenance switch flow table. So what's the difference from traditional work ?SDN There are two working modes :

(1) Active mode :

SDN Controller take Flow table The information is sent to the switch where the data plane is located at one time , If the packet received by the data plane can't find the corresponding Flow table Just throw away . Of course SDN Controller Update the data plane actively flow table Content .

The advantage of this mode is that the data plane has almost no waiting time for the controller to process packets , Greatly reduce the forwarding delay . The disadvantage is that the data plane Flow table There is a high demand for the capacity of .

(2) Passive mode :

When a new packet is received in the data plane , The control plane will be related to flowtable The information is distributed .

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