How to find the authoritative name-server for a domain name

You can use the following regular expressions separately or by combining them in a joint OR expression.

ValidIpAddressRegex = "^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$";

ValidHostnameRegex = "^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])$";

ValidIpAddressRegex matches valid IP addresses and ValidHostnameRegex valid host names. Depending on the language you use \ could have to be escaped with \.

ValidHostnameRegex is valid as per RFC 1123. Originally, RFC 952 specified that hostname segments could not start with a digit.

http://en.wikipedia.org/wiki/Hostname

The original specification of hostnames in RFC 952, mandated that labels could not start with a digit or with a hyphen, and must not end with a hyphen. However, a subsequent specification (RFC 1123) permitted hostname labels to start with digits.

Valid952HostnameRegex = "^(([a-zA-Z]|[a-zA-Z][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z]|[A-Za-z][A-Za-z0-9\-]*[A-Za-z0-9])$";

The reason this question still often arises is because, as you mentioned, somewhere somehow someone presumed as important wrote that the RFC states domain names without subdomain in front of them are not valid. If you read the RFC carefully, however, you'll find that this is not exactly what it says. In fact, RFC 1912 states:

Don't go overboard with CNAMEs. Use them when renaming hosts, but plan to get rid of them (and inform your users).

Some DNS hosts provide a way to get CNAME-like functionality at the zone apex (the root domain level, for the naked domain name) using a custom record type. Such records include, for example:

• ALIAS at DNSimple
• ANAME at DNS Made Easy
• ANAME at easyDNS
• CNAME at CloudFlare

For each provider, the setup is similar: point the ALIAS or ANAME entry for your apex domain to example.domain.com, just as you would with a CNAME record. Depending on the DNS provider, an empty or @ Name value identifies the zone apex.

ALIAS or ANAME or @ example.domain.com.

If your DNS provider does not support such a record-type, and you are unable to switch to one that does, you will need to use subdomain redirection, which is not that hard, depending on the protocol or server software that needs to do it.

I strongly disagree with the statement that it's done only by "amateur admins" or such ideas. It's a simple "What does the name and its service need to do?" deal, and then to adapt your DNS config to serve those wishes; If your main services are web and e-mail, I don' t see any VALID reason why dropping the CNAMEs for-good would be problematic. After all, who would prefer @subdomain.domain.org over @domain.org ? Who needs "www" if you're already set with the protocol itself? It's illogical to assume that use of a root-domainname would be invalid.