Q:

Default CRI implementation and default CNI implementation in K8S

Recently I am looking at the knowledge of CRI and CNI.
What are the default CRI implementation and default CNI implementation in K8S?

A:

Regarding the CRI the most common are:

Docker
CRI-O
Containerd

The most 'default' one being Docker.

Regarding the CNI:

Network plugins in Kubernetes come in a few flavors:

CNI plugins: adhere to the appc/CNI specification, designed for interoperability
Kubenet plugin: implements basic cbr0 using the bridge and host-local CNI plugins

Currently Calico is the only CNI plugin that the kubeadm project performs e2e tests against. You can find more info about installing a Pod network here.
Please let me know if that helped. 

