CNAME vs. Alias Records

Do you know when to use CNAME vs. Alias DNS records? DNS records are essential instructions that tell DNS servers how to resolve DNS query requests from web browsers. As a website owner, you must configure these records properly so users can load your site. Common types include A records and AAAA records, among others.

However, some DNS records are similar, and you can easily confuse them without the right knowledge. Two such records are the CNAME and Alias DNS records. In this blog post, we discuss the vital differences between them and when to use them. Let’s jump in!

The CNAME Record

The CNAME record can only point a domain name (such as www.yourdomain.com) to another domain name (like www.anotherdomain.com). 

However, this configuration incurs a performance penalty since an additional DNS lookup is needed to get the IP address by pulling the target’s A record.(www.anotherdomain.com). Notably, the time to perform a successful DNS resolution increases if the sites haven’t been queried by your recursive DNS server before. 

CNAME records are helpful where you want users to be directed to www.anotherdomain.com when they enter www.yourdomain.com into their browser.

The Alias Record

Like the CNAME record, you can configure an Alias record in your DNS settings to point one domain name to another domain name. 

Although CNAME and Alias records both achieve the same result, there are a few noteworthy distinctions, so what are they?

The Differences Between Alias and CNAME Records

The differences between CNAME and Alias DNS records have more to do with how they resolve queries for the target DNS record (for example, www.anotherdomain.com) and certain restrictions or advantages. Let’s take a closer look.

Resolving Domain Names

CNAME records differ from Alias records in resolving domain names to reach their destination. 

Let’s say you configure a CNAME record pointing www.yourdomain.com to www.anotherdomain.com

If someone enters www.yourdomain.com into their browser, the DNS server returns a response for www.anotherdomain.com. Their web browser then executes another DNS lookup for www.anotherdomain.com to get the IP address. 

However, the process is different for Alias records. Instead of returning a response for www.anotherdomain.com, the authoritative DNS server performs the second resolution and returns only the IP address or A record. 

CNAME vs. Alias Records Restrictions

Below are some CNAME records restrictions that aren’t present in Alias records. 

CNAME Records Can’t Coexist with other DNS Records

When you configure a CNAME record for a domain like blog.www.mywebsite.com, you can’t create any other records. Establishing another DNS record alongside a CNAME record can result in conflict, leading to erroneous results. However, this isn’t the case for Alias records, as they can coexist with other types of DNS records, such as NS records, TXT records, and SOA records in the DNS.

CNAME Records Can’t Exist in the Root Domain

You can’t configure a CNAME record in the zone apex, so it’s impossible to use a CNAME record to point a root domain to another destination. But Alias records don’t have this restriction because, like A records, they return IP addresses.  

But Alias Records Lose Geo-Targeting Data

Alias records may resolve a domain quicker and coexist with other DNS records but they have one drawback: They lose geo-targeting data. 

When a target domain name (like www.anotherdomain.com) issues queries for another domain (like www.yourdomain.com), the former’s authoritative server is responsible.

For example, if you’re in California and www.anotherdomain.com’s authoritative server is in Utah, then wwww.yourdomain.com will think you’re in Utah too, resolving a query for that geolocation. This could lead to possible misrouting.

While CNAME records are standard DNS records, Alias records are often custom DNS records.

Summary

In this post, we’ve walked you through what CNAME and Alias records are used for. We also  pointed out some significant differences.. Now, you can differentiate between both records and when you need to use them.

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