OpenFlow Concise Study Notes (original)

One, openflow to solve what problem?

1. First, a brief introduction to what is SDN, the traditional network is the computing route of each node itself, SDN is centralized control of the route. In a data center network, there is only one controller, the following can be connected to multiple switches.   After the controller has calculated the route, the flow table is sent to the switch, and the switch is forwarded according to the flow table. Run on the top is the user's app (equivalent to the computer architecture of the application software), the next layer is the SDN control plane (equivalent to the operating system), to provide interface to the app, and is responsible for centralized computing and control all the routes; the bottom layer is the network device for forwarding, the controller sends the flow table to the switch, the switch To forward. The 2.openflow specifies the protocol for interaction between the controller and the switch.
second, what is the mechanism of OpenFlow? The package processing flow for the 1.openflow switch is as follows:

Each switch has a series of tables, which specifies which message header, and what the corresponding action is, for example:

is an instance of the flow table class, which specifies that the destination IP is a type of 0x800 that is 10.1.1.1 to perform some kind of action.            receives a message that parses the message in the header, matching the flow table according to the header (12 tuples in the packet), and then doing the corresponding operation.   Usually the action list can have forwarding, discard and other actions, if the message matched to the flow table, but the action list is empty, openflow the default drop message;  But if the message does not match the flow table, it will be sent to the controller.        2. Switch-to-controller interaction:    After the switch has established a TCP connection with the controller, the communication can be communicated after the Hello message has been exchanged, such as:    acquisition/ Set configuration information, send/Send message, stream table modification, port status get/Set, error message, etc.  3. How does the controller get the networking of all switches?     via LLD message. After the controller establishes a connection with the switch and learns all the port conditions of the switch, the controller sends a LLD         text to all ports on the switch, which is not recognized after receiving the LLD message from the connected switch and is sent to the controller, The controller knows which port the two switches are connected to.  4. How does the controller install the forwarding item to the switch and correctly forward the data?     Example of HostA and HostB ping with each other:   hosta-swta--SWTB-hostb   hosta to send an ICMP message to HostB, First, you need to send the MAC address of ARP query B.    SWTA receives a sent ARP query, sends the controller through Packet-in, the controller learns the Hosta address, and sends the Hosta ARP query message to all edges        SWT, Edge SWT on     Edge link forwarding a ARP query.    HOSTB receives an ARP query, it also replies to the ARP reply, the same SWTB sends the ARP reply to the controller, and the Controller learns B's Mac.     Controller will notify the switch installation and forwarding in Shortest path, such as receiving a message with a destination address of MACB from Port 1, destined for Port 2.     Switches when the table entry is installed, the ICMP message can be forwarded in accordance with the forwarding post.

Above is I openflow superficial understanding, please master more advice:)

OpenFlow Concise Study Notes (original)