IPv4/IPv6 dual-stack networking

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Anthos clusters on bare metal supports IPv4/IPv6 dual-stack networking. This means that a cluster can accept traffic from external devices that use either Internet Protocol version 4 (IPv4) or Internet Protocol version 6 (IPv6).

Dual-stack networking assigns both IPv4 and IPv6 addresses to Pods and nodes. A Kubernetes Service can have an IPv4 address, an IPv6 address, or both.

All dual-stack clusters use flat mode for IPv6. By default, a dual-stack cluster uses island mode for IPv4, but you can configure it to use flat mode for IPv4.

To create a dual-stack cluster, your underlying network must be dual-stack enabled. If your underlying network is a single-stack IPv4 or IPv6 network, you cannot start a dual-stack cluster.

Before you begin

If your cluster nodes are running CentOS or RedHat Enterprise Linux, and they have SELinux enabled, then on each node:

  • In /etc/firewalld/firewalld.conf, set IPv6_rpfilter=no.

  • Run systemctl restart firewalld.

Overview of creating a dual-stack cluster

You can enable dual-stack networking when you create a new cluster, but you cannot enable dual-stack networking for an existing cluster.

Follow the instructions in one of the cluster creation documents.

In your configuration file, include manifests for the following:

  • A Namespace resource
  • A Cluster resource
  • One or more NodePool resources
  • One or more ClusterCIDRConfig resources

Fill in the Namespace manifest and the NodePool manifests as you would for a single-stack cluster.

In the Cluster manifest, under clusterNetwork.services.cidrBlocks, specify both an IPv4 CIDR range and an IPv6 CIDR range. This is the enabling criterion for a dual-stack cluster. That is, if you provide Service CIDR ranges for both IPv4 and IPv6, your cluster will have a dual-stack network.

In the Cluster manifest, under clusterNetwork.pods.cidrBlocks, specify an IPv4 CIDR range, but do not specify an IPv6 CIDR range. IPv6 CIDR ranges for Pods are specified in ClusterCIDRConfig manifests.

If you are using bundled load balancing, provide both IPv4 and IPv6 addresses in the loadBalancer.addressPools section of the Cluster manifest.

The ClusterCIDRConfig resources are for specifying IPv4 and IPv6 CIDR ranges for Pods. You can use a single ClusterCIDRConfig resource to specify CIDR ranges that are cluster-wide. That is, the IPv4 Pod addresses for all nodes are taken from a single CIDR range, and the IPv6 Pod addresses for all nodes are taken from a single CIDR range. Or you can use several ClusterCIDRConfig resources to specify CIDR ranges that apply to a particular node pool or a particular node.

Reachability for Pod IP addresses

A dual-stack cluster uses flat mode for IPv6 networking. The example given in this document is for a cluster that uses static flat-mode networking for IPv6. That is, the cluster is not configured to use Border Gateway Protocol (BGP).

For a cluster that uses static flat-mode networking, you must specify node and Pod IP addresses that are all part of the same subnet. This makes it possible for clients outside the cluster, but in the same layer 2 (L2) domain as the cluster nodes, to send packets directly to Pod IP addresses.

For example, suppose your cluster nodes and some other machines are all in the same L2 domain. Here is one way you could specify address ranges:

PurposeRangeNumber of addresses
Entire L2 domainfd12::/1082^20
Podsfd12::1:0/1122^16
Nodesfd12::2:0/1122^16
Other machinesfd12::3:0/1122^16
VIPsfd12::4:0/1122^16

In the preceding example, these are the key points to understand:

  • All node, Pod, and machine addresses are in the large range: fd12::/108.

  • The Pod IP addresses are in a subset of the large range.

  • The node IP addresses are in a different subset of the large range.

  • The IP addresses of other machines are in a different subset of the large range.

  • All the subset ranges are distinct from each other.

In the preceding example, each machine in the L2 domain, including the cluster nodes, must have a forwarding rule for the large range. For example:

inet fd12::/108 scope global eth0

Example: Create a dual-stack cluster

When you create a dual-stack cluster, you have various options. For example, you could have cluster-wide CIDR ranges or you could have CIDR ranges that apply to particular node pools. You could combine an IPv6 flat network with an IPv4 island-mode network. Or both your IPv4 and IPv6 networks could be flat. You could use bundled load balancing or manual load balancing.

This section gives one example of how to create a dual-stack cluster. The cluster in this example has the following characteristics:

  • An IPv4 network in island mode
  • An IPv6 network in flat mode
  • A cluster-wide IPv4 CIDR range for Pods
  • A cluster-wide IPv6 CIDR range for Pods
  • A cluster-wide IPv4 CIDR range for Services
  • A cluster-wide IPv6 CIDR range for Services
  • An IPv4 address pool to be used for Services of type LoadBalancer
  • An IPv6 address pool to be used for Services of type LoadBalancer
  • Bundled load balancing

For additional configuration examples, see Variations on using ClusterCIDRConfig.

Fill in a configuration file

Follow the instructions in one of the cluster creation documents.

In your configuration file, in the Cluster manifest:

  • For clusterNetwork.pods.cidrBlocks, provide a single IPv4 CIDR range.

  • For clusterNetwork.services.cidrBlocks, provide two CIDR ranges: one for IPv4 and one for IPv6.

  • For loadBalancer.addressPools, provide two address ranges: one for IPv4 and one for IPv6. When you create a Service of type LoadBalancer, the external IP addresses for the Service are chosen from these ranges.

Here is an example that shows the relevant portions of a Cluster manifest:

apiVersion: baremetal.cluster.gke.io/v1
kind: Cluster
metadata:
  name: "dual-stack"
  namespace: "cluster-dual-stack"

spec:
  clusterNetwork:
    pods:
      cidrBlocks:
      - "192.168.0.0/16"
    services
      cidrBlocks:
       - "172.16.0.0/20"
       - "fd12::5:0/116"
...
  loadBalancer:
    mode: "bundled"
    ...
    addressPools:
    - name: "pool-1"
      addresses:
       - "10.2.0.212-10.2.0.221"
       - "fd12::4:101-fd12::4:110"

In the same configuration file, include a manifest for a ClusterCIDRConfig.

  • Set ipv4.cidr to the same CIDR range that you provided in the Cluster manifest. This is a requirement if IPv4 is in island mode.

  • Set namespace to the same value that you provided in the Cluster manifest.

  • Set ipv6.cidr to an IPv6 CIDR range for Pods.

  • For each CIDR range, provide a value for perNodeMaskSize to specify how many Pod addresses will be assigned to each node. The number of IPv4 addresses assigned to each node must be the same as the number of IPv6 addresses assigned to each node. You must set your values for perNodeMaskSize accordingly. For example, if you want 2^8 addresses per node, set your perNodeMaskSize values as follows:

    • ipv4.perNodeMaskSize: 24 # (32 - 8 = 24)
    • ipv6.perNodeMaskSize: 120 # (128 - 8 = 120)

Here is an example of a ClusterCIDRConfig manifest:

apiVersion: baremetal.cluster.gke.io/v1alpha1
kind: ClusterCIDRConfig
metadata:
  name: "cluster-wide-ranges"
  namespace: "cluster-dual-stack"  # Must be the same as the Cluster namespace.
spec:
  ipv4:
    cidr: "192.168.0.0/16"  #  For island mode, must be the same as the Cluster CIDR.
    perNodeMaskSize: 24
  ipv6:
    cidr: "fd12::1:0/112"
    perNodeMaskSize: 120

In the preceding example:

  • The IPv4 Pod CIDR range has 2^(32-16) = 2^16 addresses. The per-node mask size is 24, so the number of addresses assigned to each node is 2^(32-24) = 2^8.

  • The IPv6 Pod CIDR range has 2^(128-112) = 2^16 addresses. The per-node mask size is 120, so the number of addresses assigned to each node is 2^(128-120) = 2^8.

Example configuration file

Finish creating the cluster

Finish creating your cluster as described in your cluster creation document.

View cluster nodes and Pods

List the cluster nodes:

kubectl --kubeconfig CLUSTER_KUBECONFIG get nodes --output yaml

Replace CLUSTER_KUBECONFIG with the path of your cluster kubeconfig file.

In the output, you can see the IPv4 and IPv6 addresses of each node. You can also see the IPv4 and IPv6 address ranges for Pods on the node. For example:

- apiVersion: v1
  kind: Node
  ...
  spec:
    podCIDR: 192.168.1.0/24
    podCIDRs:
    - 192.168.1.0/24
    - fd12::1:100/120
    providerID: baremetal://10.2.0.5
  status:
    addresses:
    - address: 10.2.0.5
      type: InternalIP
    - address: fd12::2:5
      type: InternalIP

List the Pods in the cluster:

kubectl --kubeconfig CLUSTER_KUBECONFIG get pods --all-namespaces

Choose one Pod, and list the details. For example:

kubectl --kubeconfig CLUSTER_KUBECONFIG get pod gke-metrics-agent-b9qrv \
  --namespace kube-system \
  -- output yaml

In the output, you can see the IPv4 and IPv6 addresses of the Pod. For example:

apiVersion: v1
kind: Pod
metadata:
  ...
  name: gke-metrics-agent-b9qrv
  namespace: kube-system
...
status:
  ...
  podIPs:
  - ip: 192.168.1.146
  - ip: fd12::1:11a

Variations on using ClusterCIDRConfig

The preceding example used a ClusterCIDRConfig object to specify cluster-wide Pod CIDR ranges. That is, a single IPv4 CIDR range is used for all Pods in the cluster. And a single IPv6 CIDR range is used for all Pods in the cluster.

In certain situations, you might not want to use a single CIDR range for all Pods in a cluster. For example, you might want to specify a separate CIDR range for each node pool, or you might want to specify a separate CIDR range for each node.

For example, the following ClusterCIDRConfig specifies a CIDR range for a node pool named "workers".

apiVersion: baremetal.cluster.gke.io/v1alpha1
kind: ClusterCIDRConfig
metadata:
  name: "worker-pool-ccc"
  namespace: "cluster-dual-stack"
spec:
  ipv4:
    cidr: "192.168.0.0/16"
    perNodeMaskSize: 24
  ipv6:
    cidr: "fd12::1:0/112"
    perNodeMaskSize: 120
  nodeSelector:
    matchLabels:
      baremetal.cluster.gke.io/node-pool: "workers"

The following ClusterCIDRConfig specifies a CIDR range for a single node that has IP address 10.2.0.5:

apiVersion: baremetal.cluster.gke.io/v1alpha1
kind: ClusterCIDRConfig
metadata:
  name: "range-node1"
  namespace: "cluster-dual-stack"
spec:
  ipv4:
    cidr: "192.168.1.0/24"
    perNodeMaskSize: 24
  ipv6:
    cidr: "fd12::1:0/120"
    perNodeMaskSize: 120
  nodeSelector:
    matchLabels:
      baremetal.cluster.gke.io/k8s-ip: "10.2.0.5"

Create a dual-stack Service of type ClusterIP

Here is a manifest for a Deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: "my-deployment"
spec:
  selector:
    matchLabels:
      app: "try-dual-stack"
  replicas: 3
  template:
    metadata:
      labels:
        app: "try-dual-stack"
    spec:
      containers:
      - name: "hello"
        image: "us-docker.pkg.dev/google-samples/containers/gke/hello-app:2.0"

Save the manifest in a file named my-deployment.yaml, and create the Deployment:

kubectl --kubeconfig CLUSTER_KUBECONFIG apply -f my-deployment.yaml

Replace CLUSTER_KUBECONFIG with the path of your cluster kubeconfig file.

Here is a manifest for a Service of type ClusterIP:

apiVersion: v1
kind: Service
metadata:
  name: "my-service"
spec:
  selector:
    app: "try-dual-stack"
  type: "ClusterIP"
  ipFamilyPolicy: "RequireDualStack"
  ipFamilies:
  - "IPv6"
  - "IPv4"
  ports:
  - port: 80
    targetPort: 8080

In the context of this exercise, these are the key points to understand about the preceding Service manifest:

  • The ipFamilyPolicy field is set to RequireDualStack This means both IPv6 and IPv4 ClusterIP addresses are allocated for the Service.

  • The ipFamilies field specifies the IPv6 family first and the IPv4 family second. This means that spec.ClusterIP for the Service will be an IPv6 address chosen from clusterNetwork.services.cidrBlocks in the Cluster manifest.

Save the manifest in a file named my-cip-service.yaml, and create the Service:

kubectl --kubeconfig CLUSTER_KUBECONFIG apply -f my-cip-service.yaml

List details about the Service:

kubectl --kubeconfig CLUSTER_KUBECONFIG get service my-service --output yaml

In the output, you can see the cluster IP addresses for the Service. For example:

apiVersion: v1
kind: Service
metadata:
  name: my-service
  …
spec:
  clusterIP: fd12::5:9af
  clusterIPs:
  - fd12::5:9af
  - 172.16.12.197

On a cluster node, call the Service:

curl IPV4_CLUSTER_IP
curl [IPV6_CLUSTER_IP]

The output displays a "Hello world" message:

Hello, world!
Version: 2.0.0
Hostname: my-deployment-xxx

Create a dual-stack Service of type LoadBalancer

Here is a manifest for a Service of type LoadBalancer:

apiVersion: v1
kind: Service
metadata:
  name: "my-lb-service"
spec:
  selector:
    app: "try-dual-stack"
  type: "LoadBalancer"
  ipFamilyPolicy: "RequireDualStack"
  ipFamilies:
  - "IPv6"
  - "IPv4"
  ports:
  - port: 80
    targetPort: 8080

Save the manifest in a file named my-lb-service.yaml, and create the Service:

kubectl --kubeconfig CLUSTER_KUBECONFIG apply -f my-lb-service.yaml

Recall that in your Cluster manifest, you specified a range of IPv6 addresses and a range of IPv4 addresses to be used for Services of type LoadBalancer:

  loadBalancer:
    mode: "bundled"
    ...
    addressPools:
    - name: "pool-1"
      addresses:
      - "10.2.0.112-10.2.0.221"
      - "fd12::4:101-fd12::4:110"

Your Service will be assigned an external IPv4 address chosen from the IPv4 range and an external IPv6 address chosen from the IPv6 range.

List details for the Service:

kubectl --kubeconfig CLUSTER_KUBECONFIG get service my-lb-service --output yaml

In the output, you can see the external addresses for the Service. For example:

apiVersion: v1
kind: Service
metadata:
  name: my-lb-service
...
status:
  loadBalancer:
    ingress:
    - ip: 10.2.0.213
    - ip: fd12::4:101

Possible values for ipFamilyPolicy

When you create a dual-stack Service, you can set ipFamilyPolicy to one of these values:

  • SingleStack: The controller allocates a cluster IP address for the Service, chosen from the first range specified in the Cluster manifest under clusterNetwork.services.cidrBlocks.

  • PreferDualStack: The controller allocates IPv4 and IPv6 cluster IP addresses for the Service, chosen from the ranges specified in the Cluster manifest under clusterNetwork.services.cidrBlocks. If the cluster is not a dual-stack cluster, the behavior is the same as with SingleStack.

  • RequireDualStack: The controller allocates IPv4 and IPv6 cluster IP addresses for the Service, chosen from the ranges specified in the Cluster manifest under clusterNetwork.services.cidrBlocks. It sets the value of spec.clusterIP based on the first address family specified in the Service manifest under ipFamilies.

More information

For more information about how to create dual-stack Services, see Dual-stack options on new Services.