CNI (Container Network Interface)

Khemnath chauhan
3 min readMar 16, 2021

CNI is set of standard that defines how program(plugins) should be developed and how container runtime(docker , rkt) will invoke them so that everyone adhere to single set of standard solve the common networking challenges in container runtime environment.

CNI defines a set of Responsibilities for Container Runtime.

  • Container Runtime must create network namespace.
  • Identify network the container must attach to.
  • Container Runtime to invoke Network plugin(bridge) when container is Added.
  • Container Runtime to invoke Network plugin(bridge) when container is Deleted.
  • JSON format of the Network Configuration.

In plugin side it should Support-

  • Command line arguments- ADD/DEL/CHECK.
  • Parameters — container ids, network namespace etc..
  • Must manage IP address assignment to PODs.
  • Must return result in specific format.

CNI comes with set of supported plugins — BRIDGE , VLAN , IPVLAN , MACVLAN , WINDOWS

There are also third party solutions like — flannel , Calico , weaveworks

All these implements CNI standards.

Kubelet is the process that uses the cni plugin. Some of the configuration path are.

- Check which CNI plugin it’s using:

CNI Plugin.

- Check all the plugin binaries supported:

- CNI plugin configured to be used on this kubernetes cluster?

- What binary executable file will be run by kubelet after a container and its associated namespace are created.

Look at the type field in file /etc/cni/net.d/10-flannel.conflist

Sample shared in above screen.

POD may sometime fail of the Network is not configured properly.

- Deploy weave-net networking solution to the cluster:

Reference: — https://www.weave.works/docs/net/latest/kubernetes/kube-addon/

## Weave Net can be installed onto your CNI-enabled Kubernetes cluster with a single command. Use the below commandkubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"

- Identify the name of the bridge network/interface created by weave on each node.

bridge Interface.

- What is the POD IP address range configured by weave?

IP Address Range.

- What is the default Gateway configured on the PODs scheduled on node03

get into the Image hosted on Node03

Now run the ip r to get the route of the pod. As shown below the default gateway is 10.38.0.0 which is using the interface eth0.

Get Pod route

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