Wednesday, December 23, 2009

dns @ sign means

SkyHi @ Wednesday, December 23, 2009
The "@" symbol in DNS is not proprietary to CT. In fact there is no room in the functionality of DNS (at the operational level) to allow for proprietary functions.

The "@" symbol in any DNS entry means "Primary" which is the just the domain name at face value (Ex. This is why it is almost 99% of the time used for MX (Mail exchange) record, because you send email to NOT (note: the "@" in the email address itself has nothing to do with the DNS entry for MX it is just a formatting/syntax thing) Thats not to say that you cant do that  ;), but I'll leave that to you experimental types to figure out.

This is contrary to another common symbol the "*" which is a wildcard. Which means anything not defined by another entry. This does NOT include the "Primary".

so.. heres a quick example to help you wrap your head around the concepts;

heres some DNS entries for;
Code: [Select]
Prefix   IN   Type     Value
@        IN    A
www      IN    A
*        IN    A
@        IN    MX

which means...
Code: [Select] = = = = = = fail

A HOST records can ONLY point to IP address since they are final resolvers. Meaning it has to be something a computer will know and computers only know each other on the internat by thier IP address.

CNAME and MX can be an IP address -OR- a FQDN (explained below)

Special types of entries like TXT adn PTR have different restrictions but I will not cover them to stay on topic.

FQDN = Fully Qualified Domain Name
A FQDN is a SUBDomain.DomainName.TLD (TLD is Top Level Domain, its the .com, .net
.org etc.)


I hope this helps you understand DNS a little better. I can go on about DNS but, again, wanted to stay on topic and I tend to sidetrack a lot


DNS related RFC's

As was already pointed out, the '@' symbol really hasn't got anything to with DNS. It's just a shortcut that some DNS control panels let you use to save on typing. Review whatever help system they provide for clues.

In DNS records the '@' that you are seeing is nothing more than a character used to refer to the domain name itself. It has more to do with the system or control panel that you are working in than an actual DNS entry. In simpler terms, you can view this as a place holder in an instance in which there is no character or prefix to be used. If you look at the primary A record, for instance, the '@' is often times used here since there is not a predetermined sub-domain or prefix needed for that entry.