kubernetes CNI (container networking interface)
You can go through following blogs to understand what is CNI and why it is used:
https://thenewstack.io/kubernetes-and-cni-whats-next-making-it-easier-to-write-networking-plugins/
Following link has some good information about different type of CNI plugins available and when to use what:
https://chrislovecnm.com/kubernetes/cni/choosing-a-cni-provider/
Hope this helps.