I'm adding this link to provide context for the question: NSA hacking routers https://www.wired.com/2013/09/nsa-router-hacking/
The state of SDN is pretty advanced, and a lot of it is open sourced (openflow, openvswitch). Lots of big enterprises still use Juniper and Cisco routers, and probably will for a long time, but as newer startups start to favor open source solutions, the open source SDN ecosystem should continue to grow.