Choosing a network type - Amazon ElastiCache

Choosing a network type

ElastiCache supports the Internet Protocol versions 4 and 6 (IPv4 and IPv6), allowing you to configure your cluster to accept:

  • only IPv4 connections,

  • only IPv6 connections,

  • both IPv4 and IPv6 connections (dual-stack)

IPv6 is supported for workloads using Memcached engine version 1.6.6 onward on all instances built on the Nitro system. There are no additional charges for accessing ElastiCache over IPv6.


Migration of clusters created prior to the availability of IPV6 / dual-stack is not supported. Switching between network types on newly created clusters is also not supported.

Configuring subnets for network type

If you create a cluster in an Amazon VPC, you must specify a subnet group. ElastiCache uses that subnet group to choose a subnet and IP addresses within that subnet to associate with your nodes. ElastiCache clusters require a dual-stack subnet with both IPv4 and IPv6 addresses assigned to them to operate in dual-stack mode and an IPv6-only subnet to operate as IPv6-only.

Using dual-stack

When you create a cache cluster and choose dual-stack as the network type, you then need to designate an IP discovery type – either IPv4 or IPv6. ElastiCache will default the network type and IP discovery to IPv6, but that can be changed. If you use Auto Discovery, only the IP addresses of your chosen IP type are returned returned to the Memcached client. For more information, see Automatically identify nodes in your cluster.

To maintain backwards compatibility with all existing clients, IP discovery is introduced, which allows you to select the IP type (i.e., IPv4 or IPv6) to advertise in the discovery protocol. While this limits auto discovery to only one IP type, dual-stack is still beneficial thanks to Auto Discovery, as it enables migrations (or rollbacks) from an IPv4 to an IPv6 Discovery IP type with no downtime.

TLS enabled dual stack ElastiCache clusters

When TLS is enabled for ElastiCache clusters the cluster discovery functions config get cluster return hostnames instead of IPs. The hostnames are then used instead of IPs to connect to the ElastiCache cluster and perform a TLS handshake. This means that clients won’t be affected by the IP Discovery parameter. For TLS enabled clusters the IP Discovery parameter has no effect on the preferred IP protocol. Instead, the IP protocol used will be determined by which IP protocol the client prefers when resolving DNS hostnames.

For examples on how to configure an IP protocol preference when resolving DNS hostnames, see TLS enabled dual stack ElastiCache clusters.

Using the AWS Management Console

When creating a cache cluster using the AWS Management Console, under Connectivity, choose a network type, either IPv4, IPv6 or Dual stack. If you choose dual stack, you then must select a Discovery IP type, either IPv6 or IPv4.

For more information, see Creating a Memcached cluster (console).

Using the CLI

When creating a cache cluster using the CLI, you use the create-cache-cluster command and specify the NetworkType and IPDiscovery parameters:

For Linux, macOS, or Unix:

aws elasticache create-cache-cluster \ --cache-cluster-id "cluster-test" \ --engine memcached \ --cache-node-type cache.m5.large \ --num-cache-nodes 1 \ --network-type dual_stack \ --ip-discovery ipv4

For Windows:

aws elasticache create-cache-cluster ^ --cache-cluster-id "cluster-test" ^ --engine memcached ^ --cache-node-type cache.m5.large ^ --num-cache-nodes 1 ^ --network-type dual_stack ^ --ip-discovery ipv4