ELB’s don’t have an IP address. You resolve them using a DNS name. For naked domain names like (bbc.co.uk) a IPv4 address is needed. Amazon resolves this by using Alias Records.
Alias Records allow you to resolve naked domain names (Zone Apex record) to an ELB DNS record.
Understand the difference between cName and Alias Record.
When you add an alternate domain name to a distribution, you need to create a CNAME record in your DNS configuration to route DNS queries for the domain name to your CloudFront distribution. However, you can’t create a CNAME record for the top node of a DNS namespace, also known as the zone apex; the DNS protocol doesn’t allow it. For example, if you register the DNS name example.com, the zone apex isexample.com. You can’t create a CNAME record for example.com, but you can create CNAME records forwww.example.com, newproduct.example.com, and so on.
If you’re using Amazon Route 53 as your DNS service, you can create an alias resource record set, which has two advantages over CNAME records. You can create an alias resource record set for a domain name at the zone apex (example.com). In addition, with an alias resource record set, you don’t pay for Amazon Route 53 queries.
Another important difference between cNames and Alias Records – when making requests to Route53 for a DNS record – you will be charged if using cNames, but you will not be charged if using Alias Records.
So in the exam – for scenarios that compare cName and Alias Records – Alias Records are generally the correct option.