Glen Turner (vk5tu) wrote,
Glen Turner
vk5tu

SDN: Week 1: History of SDN

Why separate control plane?

  • rapid innovation, not tied to hardware vendor

  • network-wide view

  • flexibility to introduce new services

Control plane: FORCES

  • Control Elements set forwarding table for Forwarding Elements using the FORCES interface

  • Minus: Requires standardisation, deployment, etc. But these are the exact problems.

Control plane: Routing Control Platform

  • Hijack BGP as the device to modify the forwarding plane

  • Each AS runs a RCP and communicates routes to forwarding plane using BGP.

  • Plus: Easy transition, doesn't require a new set of protocols

  • Minus: constrained by what an existing protocol can do

Custom hardware: Ethane

  • "Domain controller" computes forwarding tables for each switch

  • Needed custom switches. Ethane implemented these for OpenWRT, NetFPGA, Linux.

  • Minus: Requires custom switches which support Ethane protocol

What we want:

  • Existing protocols

  • Not custom hardware


Answer: OpenFlow

  • Take capabilities of existing hardware

  • Open those so a standard control protocol can set their behaviour

  • "Controller" communicates with switches to set forwarding table entries.

  • Most switches already implement flow tables, so only thing which is necessary for deployment is to persuade vendors to provide interface to the flow tables.


What have we learned:

  • Control and data planes should be decoupled, as coupling makes it too difficult to introduce new protocols.

  • Control plane protocols which require alterations to the hardware can't get traction.

  • Existing protocols can't express the full range of behaviour desired by network operators.

  • Open hardware allows decoupling of control.

Tags: coursera-feamster-sdn
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