Update format and remove unrelated args from dual-stack docs

Signed-off-by: pacoxu <paco.xu@daocloud.io>
Co-authored-by: Tim Bannister <tim@scalefactory.com>

content/en/docs/concepts/services-networking/dual-stack.md

@@ -242,4 +242,5 @@ Ensure your {{< glossary_tooltip text="CNI" term_id="cni" >}} provider supports
 
 
 * [Validate IPv4/IPv6 dual-stack](/docs/tasks/network/validate-dual-stack) networking
-* [Dual-stack support with kubeadm](/docs/setup/production-environment/tools/kubeadm/dual-stack-support/)
+* [Enable dual-stack networking using kubeadm
+](/docs/setup/production-environment/tools/kubeadm/dual-stack-support/)

content/en/docs/setup/production-environment/tools/kubeadm/dual-stack-support.md

@@ -4,44 +4,60 @@ feature:
   title: Dual-stack support with kubeadm
 content_type: task
 weight: 110
+min-kubernetes-server-version: 1.21
 ---
 
 <!-- overview -->
 
 {{< feature-state for_k8s_version="v1.21" state="beta" >}}
 
-IPv4/IPv6 dual-stack enables the allocation of both IPv4 and IPv6 addresses to {{< glossary_tooltip text="Pods" term_id="pod" >}} and {{< glossary_tooltip text="Services" term_id="service" >}}.
+Your Kubernetes cluster can run in [dual-stack](/docs/concepts/services-networking/dual-stack/) networking mode, which means that cluster networking lets you use either address family. In a dual-stack cluster, the control plane can assign both an IPv4 address and an IPv6 address to a single {{< glossary_tooltip text="Pod" term_id="pod" >}} or a {{< glossary_tooltip text="Service" term_id="service" >}}.
 
 <!-- body -->
 
-## Enable dual-stack via kubeadm
+## {{% heading "prerequisites" %}}
 
-Install kubeadm following the steps from the [Installing Kubeadm](/docs/setup/production-environment/tools/kubeadm/install-kubeadm/) documentation.
+You need to have installed the {{< glossary_tooltip text="kubeadm" term_id="kubeadm" >}} tool, following the steps from [Installing kubeadm](/docs/setup/production-environment/tools/kubeadm/install-kubeadm/).
 
-Make sure that nodes allow IPv6 forwarding, if not, run `sudo sysctl -w net.ipv6.conf.all.forwarding=1` on every node in the cluster.
+For each server that you want to use as a {{< glossary_tooltip text="node" term_id="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.
 
 {{< note >}}
-`kubeadm upgrade` will change `IPv6DualStack` to true by default if the feature gate is not set in an old cluster. However, cluster CIDR and service CIDR modifications are not supported.
+If you are upgrading an existing cluster then, by default, the `kubeadm upgrade` command
+changes the [feature gate](/docs/reference/command-line-tools-reference/feature-gates/)
+`IPv6DualStack` to `true` if that is not already enabled.  
+However, `kubeadm` does not support making modifications to the pod IP address range
+(“cluster CIDR”) nor to the cluster's Service address range (“Service CIDR”).
 {{< /note >}}
 
 ### Create a dual-stack cluster
 
-To create a dual-stack cluster with `kubeadm init` you can pass the following flags:
+To create a dual-stack cluster with `kubeadm init` you can pass command line arguments
+similar to the following example:
 
 ```shell
-kubeadm init --pod-network-cidr=10.244.0.0/16,fd00:10:244::/56 --service-cidr=10.96.0.0/16,fd00:10:96::/112
+# 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](https://pkg.go.dev/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1beta2) `kubeadm-config.yaml` for the primary dual-stack control plane node.
 
 ```yaml
+---
 apiVersion: kubeadm.k8s.io/v1beta2
 kind: ClusterConfiguration
 featureGates:
   IPv6DualStack: true
 networking:
-  podSubnet: 10.244.0.0/16,fd00:10:244::/56
-  serviceSubnet: 10.96.0.0/16,fd00:10:96::/112
+  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/v1beta2
 kind: InitConfiguration
@@ -50,13 +66,12 @@ localAPIEndpoint:
   bindPort: 6443
 nodeRegistration:
   kubeletExtraArgs:
-    fail-swap-on: "false"
     node-ip: 10.100.0.2,fd00:1:2:3::2
 ```
 
-`advertiseAddress` in InitConfiguration specifies the IP address the API Server will advertise it's listening on. It equals to the `--apiserver-advertise-address` flag of `kubeadm init`.
+`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.
+Run kubeadm to initiate the dual-stack control plane node:
 
 ```shell
 kubeadm init --config=kubeadm-config.yaml
@@ -65,7 +80,7 @@ kubeadm init --config=kubeadm-config.yaml
 Currently, the kube-controller-manager flags `--node-cidr-mask-size-ipv4|--node-cidr-mask-size-ipv6` are being left with default values. See [enable IPv4/IPv6 dual stack](/docs/concepts/services-networking/dual-stack#enable-ipv4ipv6-dual-stack).
 
 {{< note >}}
-Currently the `--apiserver-advertise-address` flag does not support dual-stack.
+The `--apiserver-advertise-address` flag does not support dual-stack.
 {{< /note >}}
 
 ### Join a node to dual-stack cluster
@@ -80,11 +95,8 @@ kind: JoinConfiguration
 discovery:
   bootstrapToken:
     apiServerEndpoint: 10.100.0.1:6443
-    token: 0c0z4p.dnafh6vnmouus569
-    caCertHashes: ["sha256:fcb3e956a6880c05fc9d09714424b827f57a6fdc8afc44497180905946527adf"]
 nodeRegistration:
   kubeletExtraArgs:
-    fail-swap-on: "false"
     node-ip: 10.100.0.3,fd00:1:2:3::3
 ```
 
@@ -99,16 +111,13 @@ controlPlane:
 discovery:
   bootstrapToken:
     apiServerEndpoint: 10.100.0.1:6443
-    token: 0c0z4p.dnafh6vnmouus569
-    caCertHashes: ["sha256:fcb3e956a6880c05fc9d09714424b827f57a6fdc8afc44497180905946527adf"]
 nodeRegistration:
   kubeletExtraArgs:
-    fail-swap-on: "false"
     node-ip: 10.100.0.4,fd00:1:2:3::4
 
 ```
 
-`advertiseAddress` in JoinConfiguration.controlPlane specifies the IP address the API Server will advertise it's listening on. It equals to the `--apiserver-advertise-address` flag of `kubeadm join`.
+`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`.
 
 ```shell
 kubeadm join --config=kubeadm-config.yaml ...
@@ -117,7 +126,8 @@ kubeadm join --config=kubeadm-config.yaml ...
 ### Create a single-stack cluster
 
 {{< note >}}
-Enabling the dual-stack feature doesn't mean that you need to use dual-stack addresses, i.e., you can have a single-stack cluster with the feature flag enabled.
+Enabling the dual-stack feature 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.
 {{< /note >}}
 
 In 1.21 the `IPv6DualStack` feature is Beta and the feature gate is defaulted to `true`. To disable the feature you must configure the feature gate to `false`. Note that once the feature is GA, the feature gate will be removed.
@@ -141,4 +151,4 @@ networking:
 ## {{% heading "whatsnext" %}}
 
 * [Validate IPv4/IPv6 dual-stack](/docs/tasks/network/validate-dual-stack) networking
-* [Dual-stack enabled](/docs/concepts/services-networking/dual-stack/) cluster
+* Read about [Dual-stack](/docs/concepts/services-networking/dual-stack/) cluster networking