DNS Glossary Print

An A record (short for "address record") is a type of DNS record that maps a hostname to an IP address. It is used to translate a domain name to an IP address that computers can understand.

For example, when you type "www.example.com" into a web browser, the browser first sends a request to a DNS server to resolve the domain name to an IP address. If there is an A record for "www.example.com", the DNS server will return the corresponding IP address, and the browser will then send a request to the web server at that IP address to retrieve the webpage.

A records are used to connect a domain name to a specific IP address, and they are the most basic type of DNS record. They are commonly used to map the root domain (e.g., "example.com") to an IP address, as well as subdomains (e.g., "www.example.com" or "mail.example.com").

An AAAA record (also known as a "quad-A" record) is a type of DNS record that maps a hostname to an IPv6 address. It is used to translate a domain name to an IPv6 address that computers can understand.

Like A records, AAAA records are used to connect a domain name to an IP address, but they are specifically used with IPv6 addresses. IPv6 is the successor to IPv4, which is the current version of the Internet Protocol that is most widely used. IPv6 has a larger address space than IPv4 and provides many other benefits, including better security and improved support for mobile devices.

To use AAAA records, a domain must be configured to use IPv6 and the hosting server must have an IPv6 address. When a client sends a request to a domain that has an AAAA record, the DNS server will return the corresponding IPv6 address, and the client will then send a request to the server at that address.

A CNAME record (short for "canonical name" record) is a type of DNS record that maps a hostname to another hostname, rather than to an IP address. It is used to create aliases for a domain name, so that multiple hostnames can point to the same IP address.

For example, let's say you have a website that is hosted at the IP address 192.0.2.1, and you want to make it accessible using both "www.example.com" and "blog.example.com". You could create a CNAME record for "blog.example.com" that points to "www.example.com", and then both hostnames would resolve to the same IP address.

CNAME records are often used to redirect traffic from one domain name to another, or to create shorter or more memorable hostnames that point to a longer or more complex domain name. They are also useful for creating multiple subdomains that point to the same website or service.

An MX record (short for "mail exchange" record) is a type of DNS record that is used to specify the servers that are responsible for handling email for a domain. It is used to route email messages to the correct mail servers based on the domain name.

MX records are defined in the domain's DNS zone file and are used by Simple Mail Transfer Protocol (SMTP) servers to deliver email to the correct server for a given domain. Each MX record specifies a preference value, which determines the order in which the servers should be tied, and a hostname, which specifies the server that is responsible for handling email for the domain.

For example, let's say you have a domain "example.com" and you want to receive email at the address "info@example.com". To set up your MX record, you would need to specify the hostname of the server that is responsible for handling email for your domain, as well as the preference value for that server. If you have multiple servers that can handle email for your domain, you can specify multiple MX records with different preference values.

An NS record (short for "name server" record) is a type of DNS record that is used to specify the servers that are responsible for a particular domain. It is used to delegate control of a subdomain to a different set of name servers.

Every domain has a set of name servers that are responsible for storing the DNS records for that domain. These name servers are specified in the domain's NS records, which are stored in the parent domain's DNS zone file. When a client sends a request for a domain, the DNS server checks the NS records to determine which name servers are responsible for that domain, and then sends the request to those servers to retrieve the requested information.

For example, let's say you have a domain "example.com" and you want to delegate control of the subdomain "blog.example.com" to a different set of name servers. To do this, you would create NS records in the "example.com" DNS zone file that specify the name servers for "blog.example.com". When a client sends a request for "blog.example.com", the DNS server will check the NS records for "example.com" and send the request to the specified name servers for "blog.example.com".

A PTR record (short for "pointer" record) is a type of DNS record that maps an IP address to a hostname. It is used to perform a reverse DNS lookup, which is the process of converting an IP address to a domain name.

PTR records are stored in the reverse DNS zone for a given IP address block, and they are used to associate a hostname with an IP address. When a client sends a request to a server using an IP address, the server can perform a reverse DNS lookup to determine the hostname associated with that IP address.

For example, let's say you have a server with the IP address 192.0.2.1, and you want to associate the hostname "example.com" with that IP address. To do this, you would create a PTR record in the reverse DNS zone for 192.0.2.0/24 that maps 192.0.2.1 to "example.com". When a client sends a request to 192.0.2.1, the server can perform a reverse DNS lookup to determine that the hostname for that IP address is "example.com".

An SOA record (short for "start of authority" record) is a type of DNS record that is used to specify the primary name server for a domain, as well as other important information about the domain's DNS configuration. It is the first record in a DNS zone file and defines the global parameters for the zone.

Every domain has a single SOA record, which is stored in the DNS zone file for that domain. The SOA record includes the following information:

• The primary name server for the domain
• The email address of the domain administrator
• The serial number of the zone file
• The refresh interval, which determines how often secondary name servers check for updates to the zone file
• The retry interval, which determines how long secondary name servers should wait before retrying a failed zone transfer
• The expire interval, which determines how long secondary name servers should continue to use their copy of the zone file if they are unable to contact the primary name server
• The minimum TTL, which determines the minimum time that DNS clients should cache DNS records from the zone

An SRV record (short for "service" record) is a type of DNS record that is used to specify the location of a specific service on a network. It is used to identify the hostname and port number for a service, such as a server for a specific application or protocol.

SRV records are used to allow clients to locate services dynamically, rather than having to specify a specific hostname or IP address. This is especially useful when services are hosted on multiple servers or when the hostname or IP address of a service changes frequently.

For example, let's say you have a messaging service that uses the XMPP protocol and you want to allow users to connect to the service using the hostname "chat.example.com". To do this, you would create an SRV record for the service that specifies the hostname and port number for the service, as well as the priority and weight for the server. When a client sends a request for the service, the DNS server will return the SRV record, which will tell the client the hostname and port number to use to connect to the service.

A TXT record (short for "text" record) is a type of DNS record that is used to associate text data with a hostname or domain name. It is often used to store information about a domain, such as the domain's owner or the servers that are responsible for the domain.

TXT records can be used for a variety of purposes, including:

• Storing SPF (Sender Policy Framework) records, which are used to prevent email spoofing
• Storing DMARC (Domain-based Message Authentication, Reporting, and Conformance) records, which are used to protect against email phishing and spam
• Storing Sender ID records, which are used to verify the authenticity of an email sender
• Storing information about the domain owner or administrator
• Storing other miscellaneous information about the domain

TXT records can contain any type of text data, as long as it fits within the maximum length of a DNS packet, which is usually around 255 characters.