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What does dualstack prefix mean in AWS ELB

When I add an ELB as an Alias ​​Target to AWS Route 53, it automatically adds the dualstack prefix to my ELB DNS. What does this mean?

When I try to dig , both return the same endpoints.

Note. This is an internal load balancer

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The dualstack DNS name returns both IPv6 and IPv4 records for load balancing EC2-Classic (with Internet access, no VPC).

See ELB documentation for Internet traffic balancers :

EC2-VPC

VPC load balancers only support IPv4 addresses. [...]

EC2-Classic

EC2-Classic load balancers support IPv4 and IPv6 addresses. [...]

The base public DNS name only returns IPv4 records. The public DNS name with the ipv6 prefix returns only IPv6 records. The common DNS name with the dualstack prefix returns IPv4 and IPv6 records. We recommend that you enable IPv6 support using the DNS name with the dualstack prefix to ensure that clients can access the load balancer using IPv4 or IPv6.

Although the Route53 console always adds dualstack. to the DNS name when selecting an Alias ​​target for a set of resource records A (IPv4) or AAAA (IPv6) (as indicated in and, in addition, the dualstack.* always correctly returns an IPv4 A record, only DNS names for ELFA EC2 -Classic (either the dualstack.* or ipv6.* dualstack.* ) currently returns IPv6 AAAA entries or serves as a valid alias for the AAAA entry.

You can confirm the use of dig :

 dig dualstack.[endpoint] A dualstack.[endpoint] AAAA +short

Only EL2-Classic ELB will return both IPv4 and IPv6 addresses for this command, the rest will only return IPv4 address.

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Source: https://habr.com/ru/post/1014036/

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