So this is our second post about a learning Switch and as promised, it covers OpenFlow 1.3. Before we go into the details, this is what you should already know about SDN and OpenFlow:
- General SDN Paradigm, otherwise go and read this
- A common understanding about what OpenFlow is in contrast to SDN
- What a simple learning switch is
What we are discussing in this post is the simple switch implementation that comes out of the LINC – OpenFlow software switch project as well as some basic principals from the latest OpenFlow Protocol (OFP) specification made by the Open Networking Foundation (ONF). One of the most important things you should know about OFP 1.3.x is the so called “table pipe-lining”. In previous versions of OFP there was a FlowTable in an OpenFlow enabled switch and that table stored the logic of how traffic flows through the network. Furthermore, a SDN-Controller jumps into the game when a packet that arrives at the switch doesn’t match any of the entries in the FlowTable. If this happens, we call it a “table-miss” and the switch sends the packet to the SDN-Controller. Now consider the following: In OpenFlow 1.3.x you not only have one FlowTable in an OpenFlow enabled switch, but there are as many FlowTables as the switch supports and the process how this multiple FlowTables are handled by OpenFlow is called the “table pipe-lining”. The inital behaviour isn’t that much different. If the packet arrives at the switch, the packet is always compared to the FlowTableEntries in the first the – table-0.
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