ALIAS records

Use an ALIAS record to create an alias name for another FQDN (fully-qualified domain name). In some ways, ALIAS records are similar to how CNAMEs are typically used, but without the unexpected behavior or limitations that come with CNAMEs.

ALIAS’s and CNAMEs are both frequently used when pointing your domain (or subdomain) to another hosted service, such as website hosting or a load balancer. For example:

; Configured record:
www.your-domain.com  300  ALIAS  some.load-balancer.other-provider.com

In this instance, DNScaster will itself query some.load-balancer.other-provider.com for A and AAAA records and then dynamically create A and/or AAAA records to match:

; Dynamic responses:
www.your-domain.com  300  A     192.0.2.1
www.your-domain.com  300  A     192.0.2.2
www.your-domain.com  300  AAAA  2001:db8::1
www.your-domain.com  300  AAAA  2001:db8::2

ALIAS records are only able to alias A and AAAA records, which is by far the most common case. For the less common case of needing to alias another record type, such as a TXT, use a CNAME instead.

ALIAS vs CNAME comparision ALIAS CNAME
May be used on the apex (base) domain Yes No
May have parallel (sibling) records of another record type Yes No
May have child subdomains Yes No
Client can see both the alias and original names No Yes
Record types that can be aliased A & AAAA only Any type

Comparison to alias records elsewhere

Some providers simply refer to CNAMEs as aliases, but they’re still CNAMEs. In contrast, DNScaster’s ALIAS records are a distinct type and will be dynamically converted to A and AAAA records, which is why they don’t have the limitations of an actual CNAME.

ALIAS records at some providers inherit the upstream TTL. That is, whatever TTL is returned by some.load-balancer.other-provider.com is used as-is. In contrast, DNScaster uses the TTL from the ALIAS record itself, ignoring the upstream TTL. This provides you with full control over the returned TTL, regardless of what the upstream provider does. If the upstream records are dynamic (common with CDN’s), use a lower value for the ALIAS’s TTL.

Technical details

EDNS Client Subnet information, when available, is passed through to the upstream provider during ALIAS resolution.