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DNS
The Domain Name System (DNS) is a naming system for computers or other resources connected to a network. It associates various information with domain names.
Software suites for DNS interaction
The following list shows possible DNS software suites that can be used to set up a DNS server.
- Bind is a open source package for setting up DNS
Records
A record
A (address) records map hostnames to an IP. Its basic structure is:
name. A IP
Where name is the domain to map the IP to and A is the constant for
the type of the record.
AAAA record
AAAA records are IPv6 address records that map hostnames to an IPv6 address. Its basic structure is the following.
<name>. AAAA <IPv6>
Where <name> is the domain to map the IPv6 address – in this case <IPv6> – to and AAAA is the
constant for the type of the record.
CNAME record
CNAME (canonical name) records map one domain name to another. Its basic structure is:
name. CNAME value.
Where name is the domain to map the value (another domain) to and CNAME is
the constant for the type of the record.
SRV record
Service (SRV) records define the port and hostname for specified services. Its basic structure is:
_service._proto.name. TTL class SRV priority weight port target
Where _service is the service name, _proto is the used protocoll (TCP/UDP),
name is the domain name to assign to, TTL is the DNS time to live, class
always is IN, SRV is the constant for the type of the record, priority is
the priority of the target host, weight is the relative weight for records
with the same priority, port is the port on that the service can be found and
target is the canonical hostname of the server.
Note that you need to create an A if you bind a service to a name that doesn't
already have one.
MX record
Mail Exchange – often shortened to MX – records specify which mail server is responsible for receiving emails for a domain. Its basic structure is the following.
<name>. MX <priority> <target>.
Where <name> is the domain to receive mail for, <priority> is the preference of the mail server
(lower values are preferred), <target> is the hostname of the mail server and MX is the constant
for the type of the record.
The target of an MX record must resolve to an A or AAAA record.
TXT record
TXT – short for text – records associate arbitrary textual information with a domain. Its basic structure is the following.
<name>. TXT "<text>"
Where <name> is the domain to associate the content – in this case <text> with and TXT is the
constant for the type of the record.
TXT records are commonly used for domain verification as well as technologies such as SPF, DKIM and DMARC.
PTR record
Pointer – often shortened to PTR – records map an IP address back to a hostname. Its basic structure is the following.
<ip>. PTR <hostname>.
Where <ip> is the reverse DNS representation of an IP address, <hostname> is the canonical
hostname and PTR is the constant for the type of the record.
PTR records are part of the reverse DNS namespace and are usually managed by the owner of the IP address rather than the owner of the domain. Therefor, they usually have to be set on the domain management website or (if accessible) directly in the DNS server.