ALIAS Record¶

Why should you use an ALIAS record over a CNAME record?¶

ALIAS records are used to overcome a limitation of the CNAME record. From the RFC2181:

10.1. CNAME resource records

The DNS CNAME (”canonical name”) record exists to provide the canonical name associated with an alias name. There may be only one such canonical name for any one alias.

Which means you can’t have another record along with a CNAME record. For example, this would be an invalid configuration:

www.mydomain.example 300 IN CNAME mydomain.example
www.mydomain.example 300 IN TXT "some text"

However you can’t just remove all records from your apex domain when you want to use the CNAME record. This would break another RFC from the Zone authority section:

The authoritative servers for a zone are enumerated in the NS records for the origin of the zone, which, along with a Start of Authority (SOA) record are the mandatory records in every zone.

You have a mandatory NS and SOA record on your apex domain, so if using a CNAME too there is an invalid configuration. This is where the ALIAS record comes in, to help work around this problem.

If you want to use a domain name that been provided by a CDN / DDoS provider on your apex domain, SafeDNS allows you to set the ALIAS record and we will return the address records. For example:

example.org 300 IN ALIAS example.com

In that example, when you look up mydomain.example, we will return the A and (if configured) the AAAA records of mydomain.example.

CLI

ans safedns record create mydomain.example --content "mydomain.example.cdn.example.net" --name "mydomain.example" --type "ALIAS"