Domain Concepts

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DNS Records

CNAME or "Canonical Name"

(CNAME) Record is used to define an alias hostname. A "CNAME" record takes this format:

alias.domain.name      IN     CNAME   otherhost.domain.name.

This defines alias.domain.name as an alias for the host whose canonical (standard) name is otherhost.domain.name.

"A" Record

An A record gives you the IP address of a domain. That way, users that try to go to www.example.com will get to the right IP address. An A record or "Address Record" maps a hostname to a 32-bit IPv4 address. An "A" Record takes this format (example):

Name             TTL     TYPE    DATA

ftp.domain.com   43200   A       IP Address

 

DNS Zone files are written with a "wildcard" entry, that looks like this:

*.domain.com   IN   A   xxx.xxx.xxx.xxx

 

The x's represent your particular IP address. The star takes "anything" .domain.com and points it to your server's IP address. This way, if someone mistakenly types too many or too few w's, they'll still see your website. This is also useful for setting up subdomains on your server, relieving you of the duty of adding an additional "A" record for the subdomain.

MX Record

Mail Exchange Record: Maps a domain name to a list of mail exchange servers for that domain. A zone can have one or more Mail Exchange (MX) records. These records point to hosts that accept mail messages on behalf of the host. A host can be an 'MX' for itself. MX records need not point to a host in the same zone. An 'MX' record takes this format:

host.domain.name       IN     MX      10 otherhost.domain.name.

 

IN     MX      20 otherhost2.domain.name.

 

The 'MX' preference numbers nn (value 0 to 65535) signify the order in which mailers select 'MX' records when they attempt mail delivery to the host. The lower the 'MX' number, the higher the host is in priority.

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