Dual-stack support with kubeadm [page]deterministic

Your Kubernetes cluster includes [dual-stack](/docs/concepts/services-networking/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 [Pod](#gloss:pod) or a [Service](#gloss:service).

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You need to have installed the [kubeadm](#gloss:kubeadm) tool, following the steps from [Installing kubeadm](/docs/setup/production-environment/tools/kubeadm/install-kubeadm/).

For each server that you want to use as a [node](#gloss:node), make sure it allows IPv6 forwarding.

### Enable IPv6 packet forwarding {#prerequisite-ipv6-forwarding}

To check if IPv6 packet forwarding is enabled:

```bash sysctl net.ipv6.conf.all.forwarding ``` If the output is `net.ipv6.conf.all.forwarding = 1` it is already enabled. Otherwise it is not enabled yet.

To manually enable IPv6 packet forwarding:

```bash # sysctl params required by setup, params persist across reboots cat <<EOF | sudo tee -a /etc/sysctl.d/k8s.conf net.ipv6.conf.all.forwarding = 1 EOF

# Apply sysctl params without reboot sudo sysctl --system ```

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.

> Note: If you are upgrading an existing cluster with the `kubeadm upgrade` command, `kubeadm` does not support making modifications to the pod IP address range (“cluster CIDR”) nor to the cluster's Service address range (“Service CIDR”).

### Create a dual-stack cluster

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

```shell # These address ranges are examples kubeadm init --pod-network-cidr=10.244.0.0/16,2001:db8:42:0::/56 --service-cidr=10.96.0.0/16,2001:db8:42:1::/112 ```

To make things clearer, here is an example kubeadm [configuration file](/docs/reference/config-api/kubeadm-config.v1beta4/) `kubeadm-config.yaml` for the primary dual-stack control plane node.

```yaml --- apiVersion: kubeadm.k8s.io/v1beta4 kind: ClusterConfiguration networking: podSubnet: 10.244.0.0/16,2001:db8:42:0::/56 serviceSubnet: 10.96.0.0/16,2001:db8:42:1::/112 --- apiVersion: kubeadm.k8s.io/v1beta4 kind: InitConfiguration localAPIEndpoint: advertiseAddress: "10.100.0.1" bindPort: 6443 nodeRegistration: kubeletExtraArgs: - name: "node-ip" value: "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:

```shell kubeadm init --config=kubeadm-config.yaml ```

The kube-controller-manager flags `--node-cidr-mask-size-ipv4|--node-cidr-mask-size-ipv6` are set with default values. See [configure IPv4/IPv6 dual stack](/docs/concepts/services-networking/dual-stack#configure-ipv4-ipv6-dual-stack).

> Note: The `--apiserver-advertise-address` flag does not support dual-stack.

### Join a node to dual-stack cluster

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

Here is an example kubeadm [configuration file](/docs/reference/config-api/kubeadm-config.v1beta4/) `kubeadm-config.yaml` for joining a worker node to the cluster.

```yaml apiVersion: kubeadm.k8s.io/v1beta4 kind: JoinConfiguration discovery: bootstrapToken: apiServerEndpoint: 10.100.0.1:6443 token: "clvldh.vjjwg16ucnhp94qr" caCertHashes: - "sha256:a4863cde706cfc5 …(trimmed)