DNS Records and Record Types: Some Commonly Used, and Some You Might Not Know About
Note: The audio version doesn't include code or commands. Those parts of the post can be seen in the text version. Without DNS and domain names, our experience of browsing the web would be quite different. As users, we would have to actually memorize the IP addresses of websites we want to visit, which doesn’t seem like a pleasant user experience at all. DNS is the system that associates domain names with IP addresses, so whenever we type in “securitytrails.com”, DNS uses a series of protocols to connect us with the authoritative DNS server of the domain name and serves us the content we intended to visit. DNS is one of the most popular internet services, and at the same time, is vulnerable to DNS-based attacks. Understanding DNS is an important step to prevent DNS attacks. DNS servers contain one critical component: the DNS zone file. This file contains a variety of DNS records, each of which contains specific instructions for other servers to follow in order to connect to different services on the domain, such as the web server to visit a website or a mail server. Most domain owners and users are familiar with "standard" DNS record types such as the A record, Cname, MX and TXT records, as they are responsible for the everyday actions of online users. But beyond those more commonly used is an amazingly large list of DNS record types many users haven't heard of. Let's refresh our knowledge about the most common DNS record types, and go over a list of all other, lesser-known ones in use today. What are DNS records? As mentioned, DNS records are essentially the instructions found on authoritative DNS servers and stored in their zone file. All domains need to have the few necessary records that allow a user access to a website, but there are many different DNS records involved. These include mail records, website records and informational records, among others. If you're interested in learning more about the inner workings of DNS, check out our DNS root servers post. Each DNS record has different components: the domain name; time to live (TTL), i.e. the time in seconds in which the client can store the record in cache before the information must be requested again from the DNS server; class, which is set to IN (internet) for common DNS records that involve hostnames, servers or IP addresses; the record type; and the type data, which is the information according to which the domain can be resolved. All of these components of the DNS record are structured in the DNS record syntax, which typically follows the format: Thus, a DNS record for the website.com web server will then look like this: Record types are of high interest, as they indicate the format of the data in the record and instruct on its intended use—for example, the MX record that contains the location of the mail server. Most common DNS record types Since the early days of DNS, the internet has morphed and advanced in such a way that DNS record types have constantly changed right along with it. Many have become obsolete, only to be replaced with newer types. Some of the most common DNS record types are: A record A records are among the simplest and most fundamental DNS record types. The "A" stands for "address" and when you want to visit a website, send an email or, really, do anything on the internet, the domain you enter needs to be connected with the associated IP address. A records indicate the IP address for the given domain. An example of an A record would look like: For example, if you enter "securitytrails.com" the A record will point you to the 151.101.2.132 IP address, essentially connecting your device with our website. Most websites have a single A record, but you can use multiple A records for the same domain to provide redundancy, or use a number of domain names that each have an A record pointing to the same IP address. Something important to know about A records is that they only contain IPv4 addresses. AAAA record What A records are to IPv4 addresses...