DNS Concepts: Difference between revisions
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Revision as of 18:04, 8 February 2019
Internal
Zone
A zone, also referred to as hosted zone, is a container for zone records, which include information about how you want to route traffic for a domain and all of its subdomains. A hosted zone has the same name as the corresponding domain.
Zone File
A zone file organizes the zone records for domain names and sub-domains in a DNS server. Every domain name and sub-domain has its own zone file, and each zone file contains zone records.
Domains and Sub-Domains
Sub-domains are extensions of a domain name. For example, for the "novaordis.com" domain name, "internal.novaordis.com" is a sub-domain. Although domain names might have sub-domains, the zone files for sub-domains are not considered sub-zones. All zone files are separate entities and do not have a hierarchical structure.
With godaddy.com you one can add up to 90 sub-domains per domain name. Multiple levels of sub-domains can also be added. Each sub-domain can be up to 25 characters long.
Sub-domains that point to IP addresses can be simply added as A records.
Wildcard Sub-Domain
A wildcard DNS record is a record in a DNS zone that will match requests for non-existent domain names. A wildcard DNS record is specified by using a "*" as the leftmost label (part) of a domain name, e.g. *.example.com.
Wildcard sub-domain procedures:
Zone Records
The most common records contained in a zone file are start of authority (SOA), nameserver, mail exchanger, host, and CNAME. These are described below.
Start of Authority (SOA)
Required for every zone file, the SOA record contains caching information, the zone administrator’s email address, and the master name server for the zone. The SOA also contains a number incremented with each update. As this number updates, it triggers the DNS to reload the zone data.
A (Host)
A records (also known as host records) simply point a domain name or sub domain to an IP address. Uses the A record to map an IP address to a host name. This is the most common type of record on the Internet.
"@" represents the entire domain. "@" for "novaordis.com" represents ... "novaordis.com". Entering "@" for the host name is the same as entering your domain name.
To create a wildcard A record, enter an asterisk ("*") for the host name. The wildcard makes the server respond with the IP address specified instead of an error, if the sub-domain queried does not exist within your zone file.
CNAME (Alias)
A CNAME is an alias for a host. Using CNAMEs, you can have more than one DNS name for a host. CNAME records point back to the A record, which is referred to as the "canonical name" of the CNAME. When you change the IP address in your A record, all CNAME records for that domain name automatically follow the new IP address.
MX (Mail Exchanger)
The MX record provides the mail server information for that zone to deliver email to the correct location.
TXT (Text)
This is an informational record. Use it for additional information about a host or for technical information to servers.
SRV (Service)
SRV records are resource records used to identify computers hosting specific services.
AAAA (IPv6 Host)
AAAA records store a 128-bit Internet Protocol version 6 (IPv6) address that does not fit the standard A record format. For example, 2007:0db6:85a3:0000:0000:6a2e:0371:7234 is a valid 128-bit/IPv6 address.
NS (Nameserver)
The NS record contains the name server information for the zone.
Reverse DNS
Reverse DNS (rDNS) is name resolution that looks up an IP addresses to obtain a domain name, performing the opposite function of the DNS server, which turns domain names into IP addresses.
Host Name and the Domain Name
Research the proper way of naming a machine (relative to domain name) when it has one IP address internally and another IP address externally. Now I am using a short name "not500". Also see