DNS Records Introduction: A Beginners Guide
DNS (Domain Name System) entries can quickly be updated with some propagation time, which is the length of time needed to update records across the Internet. Here are some explanations below to help you understand DNS records' basics and how it usually works in real-world scenarios.
An A record (Address Record, also known as a host record, points to an IP address's domain name or subdomain.
Usually, the domain owners assign IP addresses to a specific function such as their domain, subdomain, email, etc., allowing them to connect it from a specific server.
A CNAME (Canonical Name) record points the subdomain to another domain or another subdomain.
- www.example.com to example.com
- imap.example.com to mail.example.com
- docs.example.com to ghs.google.com.
An MX Entry (Mail Exchanger) directs email to a particular mail server(s) that has a priority in which of them will be used if the other one fails to receive the email.
A TXT (Text) record was originally intended for human-readable text. These records are dynamic and can be used for several purposes. TXT records are commonly used for Google Verification.
- SPF, Sender Policy Framework, records, those records are used by many email systems to help identify if the email is coming from a trusted source, helping filter out spam or messages pretending to be from your domain (called spoofing). More information on SPF records can be found at http://www.openspf.net/
- Another one is for DomainKeys, which is also used to verify that email came from a trusted source. More information on DomainKeys can be found at http://www.dkim.org/.
The TXT Value is what the record 'points to,' but these records aren't used to direct any traffic. Instead, they're used to provide needed information to outside sources.
An SRV (Service) record points one domain to another domain name using a specific destination port. SRV records allow specific services, such as VOIP or IM to be directed to a separate location.
- Enabling your domain to use Google's xmpp server is a good example to showcase. Google's help article states that the SRV record should be in this format:
_xmpp-server._tcp.gmail.com. IN SRV 5 0 5269 xmpp-server.l.google.com.
Under "Add DNS Record," you will need to enter the settings this way:
- Service: _xmpp-server
- Protocol: _tcp
- Host: chat (If you want to use the chat subdomain. Replace this with the subdomain that you want to use, or @ for the root domain.)
- TTL: 14400
- Type: SRV
- Priority: 5
- Weight: 0
- Port: 5269
- Points To: xmpp-server.l.google.com
The AAAA record is similar to the A record, but it allows you to point the domain to an Ipv6 address. More information on IPv6 can be found at http://ipv6.com/.
- Zone File - This is where all the DNS records are stored for a domain.
- Host Record / Hostname - This is the domain or subdomain you wish to use. The @ symbol is used to indicate the root domain itself. In our example, the Host Record 'ftp' would be for the subdomain ftp.google.com and '@' would be google.com itself.
- Points to - This is the destination server that the domain or subdomain is sending the traffic to.
- TTL - The 'time to live' value indicates the amount of time the record is cached by a DNS Server, such as your Internet service provider. The default (and lowest accepted) value is 14400 seconds (4 hours). You do not normally need to modify this value.
- Action - This allows you to modify or remove existing records.
- Weight - This is similar to priority, as it controls the order in which multiple records are used. Records are grouped with other records that have the same Priority value. As with MX Entries, lower numbers are used before higher numbers.
- Port - This is used by the server or computer to process traffic to specific services, ensuring that all traffic comes through the door that it's expected.
- Target - This is the destination the record is sending traffic to.