DNS (Domain Name System), is the service
which translates between Internet names and Internet addresses.
Internet names are the names which we use to refer to hosts on the Internet, such as www.debianhelp.co.uk.
Internet addresses are the numbers which routers use to move traffic across the Internet, such as 211.1.13.115 and
What are DNS Records ?
DNS records or Zone files are used for mapping URLs to an IPs. Located on servers called the DNS servers, these records are typically the connection of your website with the outside world. Requests for your website are forwarded to your DNS servers and then get pointed to the WebServers that serve the website or to Email servers that handle the incoming email.
Different Types of DNS Records With Syntax and Examples
Internet names are the names which we use to refer to hosts on the Internet, such as www.debianhelp.co.uk.
Internet addresses are the numbers which routers use to move traffic across the Internet, such as 211.1.13.115 and
What are DNS Records ?
DNS records or Zone files are used for mapping URLs to an IPs. Located on servers called the DNS servers, these records are typically the connection of your website with the outside world. Requests for your website are forwarded to your DNS servers and then get pointed to the WebServers that serve the website or to Email servers that handle the incoming email.
Different Types of DNS Records With Syntax and Examples
Types of DNS Records
A
AAAA
CNAME
MX
PTR
NS
SOA
SRV
TXT
NAPTR
AAAA
CNAME
MX
PTR
NS
SOA
SRV
TXT
NAPTR
The above DNS records are
mostly used in all DNS Configurations. Now we will see each one with examples.
A Record
An A record or address record.
Address Record, assigns an IP address to a domain or subdomain name. When the domain name system was designed it was recommended that no two A records refer to the same IP address.
A Record
An A record or address record.
Address Record, assigns an IP address to a domain or subdomain name. When the domain name system was designed it was recommended that no two A records refer to the same IP address.
Suppose you have the somedomain.tld domain and want to assign
10.10.0.1 IP address to your web server, then you should create an A record
with "www.somedomain.tld" as Fully Qualified Domain Name and
"10.10.0.1" in the value field.
From now on, all the requests for www.somedomain.tld will be sent to a server with that IP.
Basically is useful to use an A record when you have subdomains residing on various systems.
Usefultip: you might use a "*.somedomain.tld" A record to allow WHATEVER.somedomain.tld to be resolved to your IP, though a wildcard CNAME record is often better than a wildcard A record.
From now on, all the requests for www.somedomain.tld will be sent to a server with that IP.
Basically is useful to use an A record when you have subdomains residing on various systems.
Usefultip: you might use a "*.somedomain.tld" A record to allow WHATEVER.somedomain.tld to be resolved to your IP, though a wildcard CNAME record is often better than a wildcard A record.
Example of A Record with Syntax
example.com. IN A 69.9.64.11
Where
IN indicates Internet
A indicates the Address record.
The above example indicate that the IP Address for the domain example.com is 69.9.64.11
AAAA Record
An AAAA record or IPv6 address record maps a hostname to a 128-bit IPv6 address.
The regular DNS Address resource record is defined for a 32-bit IPv4 address, so a new one was created to allow a domain name to be associated with a 128-bit IPv6 address. The four “A”s (“AAAA”) are a mnemonic to indicate that the IPv6 address is four times the size of the IPv4 address. The AAAA record is structured in very much the same way as the A record in both binary and master file formats; it is just much larger. The DNS resource record Type value for AAAA is 28.
Example of AAAA Record with Syntax
The AAAA record is to help transition and coexistence between IPv4 and IPv6 networks.An IPv4 nameserver can provide IPv6 addresses:
linux aaaa 3ffe:1900:4545:2:02d0:09ff:fef7:6d2c
CNAME Record
A CNAME record or canonical name record makes one domain name an alias of another. The aliased domain gets all the subdomains and DNS records of the original.
You should use a CNAME record whenever you want associate a new subdomain to an already existing A record; i.e. you can make "www.somedomain.tld" to "somedomain.tld", which should already have been assigned an IP with an A record.
This allows you to have as many subdomains as you wish without having to specify the IP for every record. Use a CNAME if you have more services pointing to the same IP. This way you will have to update only one record in the convenience of a change of IP address.
Example of a CNAME record: "stuff.everybox.com CNAME www.everybox.com" where 'www.everybox.com' is an A record listing an IP address, and 'stuff.everybox.com' points to 'www.everybox.com'. It will NOT allow you to foward a domain to a specific web page. Use a webhop for that. Port numbers can be changed with webhops, as well; CNAMEs cannot change the HTTP default of 80 to any other port number.
Do not use CNAME defined hostnames in MX records. For example, this is not recommended
Example Of CNAME With syntax
mail.example.com IN CNAME mail.example.net
where
IN indicates Internet
CNAME indicates CNAME record.
MX Record
An MX record or mail exchange record maps a domain name to a list of mail exchange servers for that domain.
Example with MX Record Syntax - Single mail servers
mydomain.com. 14400 IN MX 0 mydomain.com.
The MX record shows that all emails @ mydomain.com should be routed to the mail server at mydomain.com. The DNS record shows that mydomain.com is located at 26.34.9.14. This means that email meant for test@mydomain.com will be routed to the email server at 26.34.9.14. This finishes the task of the MX record. The email server on that server then takes over, collects the email and then proceeds to distribute it to the user ``test''.
It is important that there be a dot(``.'') after the domain name in the MX record. If the dot is absent, it routes to ``mydomain.com.mydomain.com''. The number 0, indicates Preference number. Mail is always routed to the server which has the lowest Preferance number. If there is only one mail server, it is safe to mark it 0.
Using Multiple mail servers
If you want to use multiple mail servers you have to use MX record preferences.The MX record preference values indicate which mail server to use and in which order to try them when they fail or don't respond. A larger preference number is less preferred. Thus, a mail exchanger with a preference of zero (0) is always preferred over all other mail exchangers. Setting preference values to equal numbers makes mail servers equally preferred.
Example with MX Record Syntax - Multiple mail servers
mydomain.com. 14400 IN MX 0 mydomain.com.
mydomain.com. 14400 IN MX 30 server2.mydomain.com
You can have unlimited MX entries for Fallback or backup purpose.If all the MX records are equal Preference numbers, the client simply attempts all equal Preference servers in random order, and then goes to MX record with the next highest Preference number.
PTR Record
A PTR record or pointer record maps an IPv4 address to the canonical name for that host. Setting up a PTR record for a hostname in the in-addr.arpa domain that corresponds to an IP address implements reverse DNS lookup for that address. For example www.name.net has the IP address 122.0.3.16, but a PTR record maps 16.3.0.122.in-addr.arpa.
Example of PTR Record with syntax
16.3.0.122.in-addr.arpa. IN PTR name.net
Here as you see the IP Address is reversed and added with in-addr.arpa and this has come to the left side while the actual domain name has gone to right side of IN PTR.
This is mostly used as a security and an anti-spam measure wherein most of the web servers or the email servers do a reverse DNS lookup to check if the host is actually coming from where it claims to come from. It is always advisable to have a proper reverse DNS record (PTR) is been setup for your servers especially when you are running a mail / smtp server.
NS Record
An NS record or name server record maps a domain name to a list of DNS servers authoritative for that domain. Delegations depend on NS records.
NS Record Name Server Record which indicates the Authoritative Name Servers for a particular Domain. The NS records of the Authoritative Name Server for any given Domain will be listed on the Parent Server. These are called as the Delegation Records as these records on the Parent Server indicates the delegation of the domain to the Authoritative servers.
The NS record will also be listed in the Zone records of the Authoritative Name Server itself. These records are called as the Authoritative Records.
The NS records found on the Parent Server should match the NS records on the Authoritative Server as well. However, you can have NS records listed on the Authoritative server that is not listed in the Parent Server. This arrangement is normally used to configure Stealth Name Servers.
mydomain.com. 14400 IN MX 0 mydomain.com.
The MX record shows that all emails @ mydomain.com should be routed to the mail server at mydomain.com. The DNS record shows that mydomain.com is located at 26.34.9.14. This means that email meant for test@mydomain.com will be routed to the email server at 26.34.9.14. This finishes the task of the MX record. The email server on that server then takes over, collects the email and then proceeds to distribute it to the user ``test''.
It is important that there be a dot(``.'') after the domain name in the MX record. If the dot is absent, it routes to ``mydomain.com.mydomain.com''. The number 0, indicates Preference number. Mail is always routed to the server which has the lowest Preferance number. If there is only one mail server, it is safe to mark it 0.
Using Multiple mail servers
If you want to use multiple mail servers you have to use MX record preferences.The MX record preference values indicate which mail server to use and in which order to try them when they fail or don't respond. A larger preference number is less preferred. Thus, a mail exchanger with a preference of zero (0) is always preferred over all other mail exchangers. Setting preference values to equal numbers makes mail servers equally preferred.
Example with MX Record Syntax - Multiple mail servers
mydomain.com. 14400 IN MX 0 mydomain.com.
mydomain.com. 14400 IN MX 30 server2.mydomain.com
You can have unlimited MX entries for Fallback or backup purpose.If all the MX records are equal Preference numbers, the client simply attempts all equal Preference servers in random order, and then goes to MX record with the next highest Preference number.
PTR Record
A PTR record or pointer record maps an IPv4 address to the canonical name for that host. Setting up a PTR record for a hostname in the in-addr.arpa domain that corresponds to an IP address implements reverse DNS lookup for that address. For example www.name.net has the IP address 122.0.3.16, but a PTR record maps 16.3.0.122.in-addr.arpa.
Example of PTR Record with syntax
16.3.0.122.in-addr.arpa. IN PTR name.net
Here as you see the IP Address is reversed and added with in-addr.arpa and this has come to the left side while the actual domain name has gone to right side of IN PTR.
This is mostly used as a security and an anti-spam measure wherein most of the web servers or the email servers do a reverse DNS lookup to check if the host is actually coming from where it claims to come from. It is always advisable to have a proper reverse DNS record (PTR) is been setup for your servers especially when you are running a mail / smtp server.
NS Record
An NS record or name server record maps a domain name to a list of DNS servers authoritative for that domain. Delegations depend on NS records.
NS Record Name Server Record which indicates the Authoritative Name Servers for a particular Domain. The NS records of the Authoritative Name Server for any given Domain will be listed on the Parent Server. These are called as the Delegation Records as these records on the Parent Server indicates the delegation of the domain to the Authoritative servers.
The NS record will also be listed in the Zone records of the Authoritative Name Server itself. These records are called as the Authoritative Records.
The NS records found on the Parent Server should match the NS records on the Authoritative Server as well. However, you can have NS records listed on the Authoritative server that is not listed in the Parent Server. This arrangement is normally used to configure Stealth Name Servers.
Example of NS Record With syntax
example.com. IN NS ns1.live.secure.com.
where
IN indicates the Internet
NS indicates the type of record which Name Server record
The above indicates that the ns1.live.secure.com is the authoritative server for the domain example.com
Domain Name,
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Regards,
Er Ratnesh Porwal
Software Engineer
www.AeroSoftCorp.com
www.AeroSoft.in
www.AeroSoft.co.in
www.AeroSoftseo.com
On Line Assistence :
Gtalk : ratnesh.aerosoft@gmail.com
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Rediff Bol ratnesh.AeroSoft@rediffmail.
Er Ratnesh Porwal
Software Engineer
www.AeroSoftCorp.com
www.AeroSoft.in
www.AeroSoft.co.in
www.AeroSoftseo.com
On Line Assistence :
Gtalk : ratnesh.aerosoft@gmail.com
Y! Messenger : ratnesh.AeroSoft@yahoo.com
Rediff Bol ratnesh.AeroSoft@rediffmail.
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