Dual-stack support with kubeadm

    Your Kubernetes cluster includes dual-stack networking, which means that cluster networking lets you use either address family. In a cluster, the control plane can assign both an IPv4 address and an IPv6 address to a single or a Service.

    You need to have installed the kubeadm tool, following the steps from .

    For each server that you want to use as a node, make sure it allows IPv6 forwarding. On Linux, you can set this by running run sysctl -w net.ipv6.conf.all.forwarding=1 as the root user on each server.

    You need to have an IPv4 and and IPv6 address range to use. Cluster operators typically use private address ranges for IPv4. For IPv6, a cluster operator typically chooses a global unicast address block from within 2000::/3, using a range that is assigned to the operator. You don’t have to route the cluster’s IP address ranges to the public internet.

    The size of the IP address allocations should be suitable for the number of Pods and Services that you are planning to run.

    To create a dual-stack cluster with kubeadm init you can pass command line arguments similar to the following example:

    To make things clearer, here is an example kubeadm configuration file kubeadm-config.yaml for the primary dual-stack control plane node.

    1. ---
    2. apiVersion: kubeadm.k8s.io/v1beta3
    3. kind: ClusterConfiguration
    4. networking:
    5.   podSubnet: 10.244.0.0/16,2001:db8:42:0::/56
    6.   serviceSubnet: 10.96.0.0/16,2001:db8:42:1::/112
    7. apiVersion: kubeadm.k8s.io/v1beta3
    8. kind: InitConfiguration
    10.   advertiseAddress: "10.100.0.1"
    11.   bindPort: 6443
    12. nodeRegistration:
    13.   kubeletExtraArgs:
    14.     node-ip: 10.100.0.2,fd00:1:2:3::2

    advertiseAddress in InitConfiguration specifies the IP address that the API Server will advertise it is listening on. The value of advertiseAddress equals the --apiserver-advertise-address flag of kubeadm init

    Run kubeadm to initiate the dual-stack control plane node:

    The kube-controller-manager flags --node-cidr-mask-size-ipv4|--node-cidr-mask-size-ipv6 are set with default values. See .

    Before joining a node, make sure that the node has IPv6 routable network interface and allows IPv6 forwarding.

    Here is an example kubeadm kubeadm-config.yaml for joining a worker node to the cluster.

    1. apiVersion: kubeadm.k8s.io/v1beta3
    2. kind: JoinConfiguration
    3. discovery:
    4.     apiServerEndpoint: 10.100.0.1:6443
    5.     token: "clvldh.vjjwg16ucnhp94qr"
    6.     caCertHashes:
    7.     - "sha256:a4863cde706cfc580a439f842cc65d5ef112b7b2be31628513a9881cf0d9fe0e"
    8.     # change auth info above to match the actual token and CA certificate hash for your cluster
    9. nodeRegistration:
    10.   kubeletExtraArgs:
    11.     node-ip: 10.100.0.3,fd00:1:2:3::3

    Also, here is an example kubeadm configuration file kubeadm-config.yaml for joining another control plane node to the cluster.

    advertiseAddress in JoinConfiguration.controlPlane specifies the IP address that the API Server will advertise it is listening on. The value of advertiseAddress equals the --apiserver-advertise-address flag of kubeadm join.

    1. kubeadm join --config=kubeadm-config.yaml

    Note: Dual-stack support doesn’t mean that you need to use dual-stack addressing. You can deploy a single-stack cluster that has the dual-stack networking feature enabled.

    What’s next

    • networking
    • Read about Dual-stack cluster networking