Guide for beginners
A system of DNS records works on internet and in computer networks for translating the domain names to IP addresses and provides a easier communication and navigation on internet. It is often compared to a telephone list, for it adds a (domain) name to an IP address.
Thanks to the DNS, the user is not required to remember the IP address of the website, only the domain name. System of DNS manages the navigation. When the website name is entered, the web browser will check on which DNS server the records for that particular website are and on the DNS server it searches for the IP address that is connected to the website. DNS records consist of several types of records – each has its own role.
What type of DNS exists?
DNS record system is designed for internet and computer networks to translate domain names to IP addresses and thus simplify communication on the internet. It is often described as phone book for it connects IP addresses to domain names just like phone book connects phone numbers to personal names.
Thanks to DNS the user need not to remember IP address of the website, only its name. DNS system will make sure to navigate the user to the correct website. Internet brouwser will gather the data about DNS server where website’s records are located and on this server will acquire the IP address for the domain. There are multiple DNS records on the domain. Here are the most used types of records:
A records
The DNS record A record serves to designate specific IP address from which the content of the domain (or subdomain) is loaded. You can set a different IP address for each different subdomain, as much as you need. IP address has to be set in IPv4 format (e.g. 37.9.168.19). For IPv6 address you need to use AAAA record.
How is A record represented
@ 600 IN A 37.9.175.13
Example
Domain mydomain.tld has an A record with IP address 37.9.175.13. That means that after entering mydomain.tld to a web browser, domain will display content on the server with filled IP address.
MX records
The MX records (mail exchange) serves to specify which server should manage your e-mails. You can set up multiple MX records for one domain and your e-mails will be managed by specific server depending on its priority. Value of MX record is inserted as a text (e.g. mailing1.mydomain.com) and not as an IP.
How is MX record represented
@ 600 IN MX 10 mailin1.mydomain.tld. @ 600 IN MX 100 mailin2.mydomain.tld.
Example
For mydomain.tld there is MX record with value “ASPMX.L.GOOGLE.COM”. In this case all e-mails sent to mailbox@mydomain.tld will be directed to the Google mail server.
NS records
NS records, also called nameservers, determines where are your DNS records located. Editing of NS records is administered at the national registry (WHOIS) of the domain, who knows, where to send all inquiries about your domain. NS records are superior to all other DNS records.
How are NS records represented
@ 86400 IN NS ns1.websupport.cz. @ 86400 IN NS ns2.websupport.cz. @ 86400 IN NS ns3.websupport.eu.
Example
Your domain mydomain.tld does not have NS records by the central registry (e.g.CZ-NIC for CZ domains). That means all searches of your domain will be stopped at the central registry and won’t be processed. If you set your NS records to ns1.websupport.cz, ns2.websupport.cz, ns3.websupport.eu, all searches will locate DNS at Active24 and the website will display your content properly.
CNAME records
The CNAME record (Canonical Name record) is designed to forward any subdomain to a different subdomain or domain. It means that subdomain is forwarded to specific domain and not the IP address. Its convenient since there is no change required if the IP of the destination address is changed.
How is the CNAME record represented
shop 600 IN CNAME www.myshoptet.com.
Subdomain shop.mydomain.tld is to be directed to www.myshoptet.com by CNAME record. That means that after domain shop.mydomain.tld is searched by web browser, content on the Shoptet service will be displayed.
AAAA records
The AAAA records are alternative to A records. They are used if your server you want to display your content from is using IPv6 IP address.
How is the AAAA record represented
* 600 IN AAAA 2A03: 2880: 2110: df07: face: b00c: 0:1.
Example
You want to direct your subdomain blog.mydomain.tld to a server with IP address 2A03: 2880: 2110: df07: face: b00c: 0: 1 (IPv6 facebook). Since it is not regular IP address IPv4 used in A records, you can simply use AAAA record.
TXT records
The TXT records add some text information to DNS records of the domain. They are often used for domain verification purposes or to add additional information in regards to connecting your domain with external services.
How is the TXT record represented
mydomain.tld 600 IN TXT "google-site-verification= rXOxyZounnZasA8Z7oaD3c14JdjS9aKSWvsR1EbUSIQ"
Example
If you want to use Google Apps on your domain, you will be asked to verify domain ownership. One of the options is to add a specific record to the DNS records. This record will be added as TXT record.
SPF records
The SPF record (Sender Policy Framework) is a type of TXT record which contains information about which SMTP servers (IP addresses) are allowed to send e-mails from your domain. Main purpose of this record is to limit falsification of the e-mail sender and thus prevent SPAM.
How is the SPF record represented
v=spf1 a mx include:_spf.websupport.cz ?all
This record represents that the mail server smtp.websupport.cz is authorised SMTP server for your domain. If you send a message to smpt.web4u.cz this server will check the message via SPF records. If the server you send from and the server in the SPF record match, the message will be processed.
SRV record
The SRV record is designed to designate server addresses for specific services. Its speciality is to divide load to multiple addresses based on weight and priority.
How is the SRV record represented
_xmpp-client._tcp.mojadomen.sk 1800 SRV 5 0 5222 talk.l.google.com
Example
If you want to use chat included in the Google Apps service on your domain, you will be asked to add specific DNS record to you domain DNS e.g. “_xmpp-client._tcp.mojadomen.sk 1800 SRV 5 0 5222 talk.l.google.com”. You will use SRV record for that.
CAA záznamy
The CAA records (Certification Authority Authorisation) is used to determine certificate authority that can issue SSL certificates for specific domain. CAA record may be set for a domain as a whole or for specific subdomains.
How is the CAA record represented
@ 600 IN CAA 128 issue "letsencrypt.org"
SSHFP records
The DNS SSHFP record (Secure Shell fingerprint record) contains fingerprint of the public keys used for SSH connection. They are used especially along domains with allowed DNSSEC. SSHFP record checks during the SSH client connection attempt if the public keys are matching to the keys on the server and if it is secure to connect the client to the server.
How is the SSHFP record presented
host.example.com. 1800 SSHFP 2 1 123456789abcdef67890123456789abcdef67890
TLSA records
The TLS Authentication record (TLSA) is used to associate a TLS server certificate or public key with the domain name where the record is found. With a TLSA record, you can store the fingerprint of a TLS/SSL certificate in the DNS of your domain.
TLSA records can only be trusted if DNSSEC is enabled on your domain so the DNS response is verified.
How the TLSA record is presented
_100._tcp.www.domain.tld. IN TLSA 3 1 1 1fff7351cdb3957d2d3edd0f7d48bb6246f25361006c1f83379b85c6f3071adc
LOC records
The LOC record is used for information about geographical location of the domain. The records consists of Latitude Longitude in degrees (d1) [0..90], (d2) [0..180], minutes (m1, m2) [0..59] and seconds (s1,s2) [0..59.999] and Altitude information (alt) [-100000,00..42849672,95] as well as host/subnet physical size and location accuracy in meters (siz, hp, vp) [0..90000000,00]
How is the LOC record presented
LOC record statdns.net. IN LOC 52 22 23.000 N 4 53 32.000 E -2.00m 0.00m 10000m 10m
CERT records
The CERT record stores the certificate and Certificate revocation list (CRL) for cryptographic keys. DNS records consists of type of certificate [0..65535], key tag [0..65535], used algorythm [0-65535], certificate or CRL in Base 64 formate.
DNS Check
We can check how the DNS records are set on the domain in multiple ways.
DNS checker
For example on this site you can find the means to display the most used DNS records. Simply enter the name of the domain (or subdomain) and select which record you wan to check.
Command line
What DNS records are set on the domain can be check via terminal supporting host command. For example to see what DNS A record is on domain active24.cz, use the command:
host -t a active24.cz active24.cz has address 37.9.169.171 active24.cz has address 37.9.169.172 active24.cz has address 37.9.169.173
We can also check other DNS records, e.g. DNS MX records:
host -t mx active24.cz active24.cz mail is handled by 10 mx10.active24.cz. active24.cz mail is handled by 100 mx20.active24.cz.