IPv4/IPv6 dual-stack

IPv4/IPv6 dual-stack networking enables the allocation of both IPv4 and IPv6 addresses to Pods and Services.

IPv4/IPv6 dual-stack networking is enabled by default for your Kubernetes cluster starting in 1.21, allowing the simultaneous assignment of both IPv4 and IPv6 addresses.

Supported Features

IPv4/IPv6 dual-stack on your Kubernetes cluster provides the following features:

• Dual-stack Pod networking (a single IPv4 and IPv6 address assignment per Pod)
• IPv4 and IPv6 enabled Services
• Pod off-cluster egress routing (eg. the Internet) via both IPv4 and IPv6 interfaces

Prerequisites

The following prerequisites are needed in order to utilize IPv4/IPv6 dual-stack Kubernetes clusters:

• Kubernetes 1.20 or later

  For information about using dual-stack services with earlier Kubernetes versions, refer to the documentation for that version of Kubernetes.

• Provider support for dual-stack networking (Cloud provider or otherwise must be able to provide Kubernetes nodes with routable IPv4/IPv6 network interfaces)

• A network plugin that supports dual-stack networking.

Configure IPv4/IPv6 dual-stack

To configure IPv4/IPv6 dual-stack, set dual-stack cluster network assignments:

• kube-apiserver:
  • --service-cluster-ip-range=<IPv4 CIDR>,<IPv6 CIDR>
• kube-controller-manager:
  • --cluster-cidr=<IPv4 CIDR>,<IPv6 CIDR>
  • --service-cluster-ip-range=<IPv4 CIDR>,<IPv6 CIDR>
  • --node-cidr-mask-size-ipv4|--node-cidr-mask-size-ipv6 defaults to /24 for IPv4 and /64 for IPv6
• kube-proxy:
  • --cluster-cidr=<IPv4 CIDR>,<IPv6 CIDR>
• kubelet:
  • --node-ip=<IPv4 IP>,<IPv6 IP>
    • This option is required for bare metal dual-stack nodes (nodes that do not define a cloud provider with the --cloud-provider flag). If you are using a cloud provider and choose to override the node IPs chosen by the cloud provider, set the --node-ip option.
    • (The legacy built-in cloud providers do not support dual-stack --node-ip.)

Services

You can create Services which can use IPv4, IPv6, or both.

The address family of a Service defaults to the address family of the first service cluster IP range (configured via the --service-cluster-ip-range flag to the kube-apiserver).

When you define a Service you can optionally configure it as dual stack. To specify the behavior you want, you set the .spec.ipFamilyPolicy field to one of the following values:

• SingleStack: Single-stack service. The control plane allocates a cluster IP for the Service, using the first configured service cluster IP range.
• PreferDualStack: Allocates both IPv4 and IPv6 cluster IPs for the Service when dual-stack is enabled. If dual-stack is not enabled or supported, it falls back to single-stack behavior.
• RequireDualStack: Allocates Service .spec.clusterIPs from both IPv4 and IPv6 address ranges when dual-stack is enabled. If dual-stack is not enabled or supported, the Service API object creation fails.
  • Selects the .spec.clusterIP from the list of .spec.clusterIPs based on the address family of the first element in the .spec.ipFamilies array.

If you would like to define which IP family to use for single stack or define the order of IP families for dual-stack, you can choose the address families by setting an optional field, .spec.ipFamilies, on the Service.

You can set .spec.ipFamilies to any of the following array values:

• ["IPv4"]
• ["IPv6"]
• ["IPv4","IPv6"] (dual stack)
• ["IPv6","IPv4"] (dual stack)

The first family you list is used for the legacy .spec.clusterIP field.

Dual-stack Service configuration scenarios

These examples demonstrate the behavior of various dual-stack Service configuration scenarios.

Dual-stack options on new Services

1. This Service specification does not explicitly define .spec.ipFamilyPolicy. When you create this Service, Kubernetes assigns a cluster IP for the Service from the first configured service-cluster-ip-range and sets the .spec.ipFamilyPolicy to SingleStack. (Services without selectors and headless Services with selectors will behave in this same way.)

   service/networking/dual-stack-default-svc.yaml

   apiVersion: v1
   kind: Service
   metadata:
     name: my-service
     labels:
       app.kubernetes.io/name: MyApp
   spec:
     selector:
       app.kubernetes.io/name: MyApp
     ports:
       - protocol: TCP
         port: 80
   

2. This Service specification explicitly defines PreferDualStack in .spec.ipFamilyPolicy. When you create this Service on a dual-stack cluster, Kubernetes assigns both IPv4 and IPv6 addresses for the service. The control plane updates the .spec for the Service to record the IP address assignments. The field .spec.clusterIPs is the primary field, and contains both assigned IP addresses; .spec.clusterIP is a secondary field with its value calculated from .spec.clusterIPs.

   • For the .spec.clusterIP field, the control plane records the IP address that is from the same address family as the first service cluster IP range.
   • On a single-stack cluster, the .spec.clusterIPs and .spec.clusterIP fields both only list one address.
   • On a cluster with dual-stack enabled, specifying RequireDualStack in .spec.ipFamilyPolicy behaves the same as PreferDualStack.
   service/networking/dual-stack-preferred-svc.yaml

   apiVersion: v1
   kind: Service
   metadata:
     name: my-service
     labels:
       app.kubernetes.io/name: MyApp
   spec:
     ipFamilyPolicy: PreferDualStack
     selector:
       app.kubernetes.io/name: MyApp
     ports:
       - protocol: TCP
         port: 80
   

3. This Service specification explicitly defines IPv6 and IPv4 in .spec.ipFamilies as well as defining PreferDualStack in .spec.ipFamilyPolicy. When Kubernetes assigns an IPv6 and IPv4 address in .spec.clusterIPs, .spec.clusterIP is set to the IPv6 address because that is the first element in the .spec.clusterIPs array, overriding the default.

   service/networking/dual-stack-preferred-ipfamilies-svc.yaml

   apiVersion: v1
   kind: Service
   metadata:
     name: my-service
     labels:
       app.kubernetes.io/name: MyApp
   spec:
     ipFamilyPolicy: PreferDualStack
     ipFamilies:
     - IPv6
     - IPv4
     selector:
       app.kubernetes.io/name: MyApp
     ports:
       - protocol: TCP
         port: 80
   

Dual-stack defaults on existing Services

These examples demonstrate the default behavior when dual-stack is newly enabled on a cluster where Services already exist. (Upgrading an existing cluster to 1.21 or beyond will enable dual-stack.)

1. When dual-stack is enabled on a cluster, existing Services (whether IPv4 or IPv6) are configured by the control plane to set .spec.ipFamilyPolicy to SingleStack and set .spec.ipFamilies to the address family of the existing Service. The existing Service cluster IP will be stored in .spec.clusterIPs.

   service/networking/dual-stack-default-svc.yaml

   apiVersion: v1
   kind: Service
   metadata:
     name: my-service
     labels:
       app.kubernetes.io/name: MyApp
   spec:
     selector:
       app.kubernetes.io/name: MyApp
     ports:
       - protocol: TCP
         port: 80
   

   You can validate this behavior by using kubectl to inspect an existing service.

   kubectl get svc my-service -o yaml
   

   apiVersion: v1
   kind: Service
   metadata:
     labels:
       app.kubernetes.io/name: MyApp
     name: my-service
   spec:
     clusterIP: 10.0.197.123
     clusterIPs:
     - 10.0.197.123
     ipFamilies:
     - IPv4
     ipFamilyPolicy: SingleStack
     ports:
     - port: 80
       protocol: TCP
       targetPort: 80
     selector:
       app.kubernetes.io/name: MyApp
     type: ClusterIP
   status:
     loadBalancer: {}
   

2. When dual-stack is enabled on a cluster, existing headless Services with selectors are configured by the control plane to set .spec.ipFamilyPolicy to SingleStack and set .spec.ipFamilies to the address family of the first service cluster IP range (configured via the --service-cluster-ip-range flag to the kube-apiserver) even though .spec.clusterIP is set to None.

   service/networking/dual-stack-default-svc.yaml

   apiVersion: v1
   kind: Service
   metadata:
     name: my-service
     labels:
       app.kubernetes.io/name: MyApp
   spec:
     selector:
       app.kubernetes.io/name: MyApp
     ports:
       - protocol: TCP
         port: 80
   

   You can validate this behavior by using kubectl to inspect an existing headless service with selectors.

   kubectl get svc my-service -o yaml
   

   apiVersion: v1
   kind: Service
   metadata:
     labels:
       app.kubernetes.io/name: MyApp
     name: my-service
   spec:
     clusterIP: None
     clusterIPs:
     - None
     ipFamilies:
     - IPv4
     ipFamilyPolicy: SingleStack
     ports:
     - port: 80
       protocol: TCP
       targetPort: 80
     selector:
       app.kubernetes.io/name: MyApp
   

Switching Services between single-stack and dual-stack

Services can be changed from single-stack to dual-stack and from dual-stack to single-stack.

1. To change a Service from single-stack to dual-stack, change .spec.ipFamilyPolicy from SingleStack to PreferDualStack or RequireDualStack as desired. When you change this Service from single-stack to dual-stack, Kubernetes assigns the missing address family so that the Service now has IPv4 and IPv6 addresses.

   Edit the Service specification updating the .spec.ipFamilyPolicy from SingleStack to PreferDualStack.

   Before:

   spec:
     ipFamilyPolicy: SingleStack
   

   After:

   spec:
     ipFamilyPolicy: PreferDualStack
   

2. To change a Service from dual-stack to single-stack, change .spec.ipFamilyPolicy from PreferDualStack or RequireDualStack to SingleStack. When you change this Service from dual-stack to single-stack, Kubernetes retains only the first element in the .spec.clusterIPs array, and sets .spec.clusterIP to that IP address and sets .spec.ipFamilies to the address family of .spec.clusterIPs.

Headless Services without selector

For Headless Services without selectors and without .spec.ipFamilyPolicy explicitly set, the .spec.ipFamilyPolicy field defaults to RequireDualStack.

Service type LoadBalancer

To provision a dual-stack load balancer for your Service:

• Set the .spec.type field to LoadBalancer
• Set .spec.ipFamilyPolicy field to PreferDualStack or RequireDualStack

Egress traffic

If you want to enable egress traffic in order to reach off-cluster destinations (eg. the public Internet) from a Pod that uses non-publicly routable IPv6 addresses, you need to enable the Pod to use a publicly routed IPv6 address via a mechanism such as transparent proxying or IP masquerading. The ip-masq-agent project supports IP masquerading on dual-stack clusters.

Windows support

Kubernetes on Windows does not support single-stack "IPv6-only" networking. However, dual-stack IPv4/IPv6 networking for pods and nodes with single-family services is supported.

You can use IPv4/IPv6 dual-stack networking with l2bridge networks.

You can read more about the different network modes for Windows within the Networking on Windows topic.

What's next

• Validate IPv4/IPv6 dual-stack networking
• Enable dual-stack networking using kubeadm