CNAME record explained

CNAME record

The CNAME record is one of the first DNS records that you will read about when you are starting with DNS management. It has a very important task to do, showing the true domain name for the subdomains, making it really an essential DNS record. It saves time and makes it easier to manage the DNS.

CNAME explained completely

There are two parts in the CNAME’s name. C stands for canonical, and it wants to show which is the true domain name for the one that you are trying to resolve. The NAME is obvious. It stands for name, as in hostname.

The purpose of the CNAME record is to point one hostname to another. You can point different subdomains to the domain name. That way, you don’t need to add any other records for the subdomain because it will automatically redirect to the domain name.

If you have just a single DNS record for each subdomain, you will have far fewer DNS records, and the administration of your domain will be a lot easier.

CNAME records can be used to point:

www.domain.com to domain.com

blog.domain.com to domain.com

mail.domain.com to domain.com

newyork.domain.com to domain.com

Because of the way the CNAME record works, if the host (subdomain) already has other DNS records like A, MX, etc., you can’t create a CNAME record. And if you first create a CNAME record in the zone, you can’t create any other type of record in that zone.

Inside a CNAME record, you will see:

Host – the name of the subdomain that you want to point to the main domain name.

Type – CNAME.

Points to – the domain name. All of the CNAME records will point to this one.

TTL – time to live for that DNS record.

How to lookup a CNAME record?

If you are on Windows, the easiest and the safest way to check a CNAME record is to use the nslookup command. Go to the cmd (Command Prompt). Type “nslookup”, and press Enter. Now type “set type=cname”, and press Enter. The last pass is to write down the hostname, which you want to check. See this example, “mail.bing.com” and you will see the canonical name “star-bing-com.a-0001.a-msedge.net”.

If you are using Linux, go for the dig command. Open the Terminal and type “dig cname mail.bing.com,” and you will see the same “star-bing-com.a-0001.a-msedge.net” plus additional information. Dig command has very rich answers.

CNAME vs ALIAS

There is a newer type of DNS record called ALIAS that also points one hostname to another. It can do almost all that the CNAME can, but it can coexist with other records and can be added to the apex zone.

CNAME vs A record

The CNAME and the A records are very different. CNAME point one hostname to another while the A record points the domain name to an IP address. Also, if you want to resolve a domain, and first you get a CNAME, then you will need the A record too. So, the CNAME will take 2 queries instead of 1.

If you are interested in DNS records, check our article about the DNS CAA record!

Reverse DNS and PTR record – everything you need to know

Reverse DNS

Reverse DNS is a key component of the configuration of your mail server. 

Not having Reverse DNS can mean not sending emails! Without well-configured Reverse DNS zone and PTR records, the rest of the email servers can’t check your domain’s IP address and discard your messages or throw them into the spam box.

Everything you need to know about Reverse DNS

A Reverse DNS is a service that provides Reverse DNS zones for your domain. The Reverse DNS zones serve to host PTR records that can be used for verification purposes, to check the IP addresses and if they lead to the correct hostnames.

The mail servers of other companies that want to send you emails need to make sure that the IP address that they are seen truly belongs to your domain. Otherwise, they can send the emails to another place, and criminals might use the information.

It is used for different services, too, for the same purpose to verify that a particular IP address belongs to the domain name.

The Reverse DNS can be used to point IPv4 or IPv6 addresses to hostnames. You can add both PTR records with IPv4 and IPv6 addresses inside the same Reverse DNS zone.

Why does the Reverse DNS matter?

The Reverse DNS matters because without it, your emails might not arrive at their destination. The mail servers of the receivers will check your PTR records, among other DNS records, and if they don’t find them, they might not trust your domain and discard the emails you are sending them.

Everything you need to know about the PTR record

The PTR record is the DNS type of record that you use for Reverse DNS and links IP addresses (it can work both with IPv4 and IPv6 addresses) to the domain name. When the receiving mail servers whats to check the origin of an email, they will perform a DNS Reverse lookup, and they will search for PTR records. The PTR records will guarantee that the IP truly belongs to the domain name.

How to perform Reverse lookup and PTR lookup?

You can perform a Reverse lookup using the nslookup command. The nslookup command is available on all popular computer OSes.

For Windows users, use the Command Prompt, and for macOS or Linux users, go for the Terminal application. There you will need to type the following nslookup command:

nslookup -type=ptr 91.198.174.194

We will specify the type of DNS record that we want, and for the Reverse lookup, we need the PTR record.

We are using the IPv4 address 91.198.174.194, but you can change it with whatever you like, so you can verify your domain or somebody else domain.

The result will be the name of the host. We can compare if this name is related to the domain we were expecting.

Conclusion

Now you know that Reverse DNS is and how it uses PTR DNS records to point IP addresses to domain names. Start using them for your domain and reduce the bouncing rate of your sent emails. It is not hard. It is just a matter of knowledge.

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