CODEWITHSUNDEEP
sdnopenflow
Filip Kowalski
Filip Kowalski

Reputation: 154

Difference between instructions and actions in OpenFlow

In OpenFlow protocol we have a flow table (or multiple flow tables). Each flow table in the switich contains a set of flow entries. Each flow entry contains header fields, counters and a set of instructions or actions to be applied. Instrucions are like "add this action to action set" (write-actions instruction) or "clear action set" (clear-actions instruction), and actions are like "output to port X" (output action) or "drop this packet" (drop action). But how does work ? what exactly is in the flow entry, an action or an instruction ? or maybe both are ? what exactly is an action set ? could someone give me a little exmaple that uses these terms ?

Upvotes: 3

Views: 2335

Answers (1)

Felipe Volpato
Felipe Volpato

Reputation: 401

"Actions can discard, modify, queue, or forward the packet. In version 1.0 of the OpenFlow protocol the Action set is modified directly by the Actions list in the FlowMod message; however, in 1.1.0 and subsequent versions the the protocol, the Action set is modified by the Instruction structure carried in the FlowMod. An Instruction may carry an Actions list to update the Action set, or be applied immediately to the packet bypassing the Action set".

ref. (http://flowgrammable.org/sdn/openflow/actions/#ofp_1_4)

In other words, when a packet matches a particular OpenFlow flow, the switch running OpenFlow v1.0 applies a set of actions to the packet. Now, with the new OpenFlow version, instead of applying a set of actions, the switch applies a flow instruction to a matching packet.

According to OpenFlow specification 1.5.1 (https://www.opennetworking.org/images/stories/downloads/sdn-resources/onf-specifications/openflow/openflow-switch-v1.5.1.pdf), the instruction set associated with a flow entry contains a maximum of one instruction of each type, following the order: Apply-Actions, Clear-Actions, Write-Actions, Write-Metadata, Stat-Trigger or Goto-Table.

Upvotes: 1

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