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Setting up a DNS server
There are two ways to configure DNS. You can use your ISP's DNS server or you set up your own DNS server. In the first case you don't have to register the name server (your ISP already did) with a domain registrar, in the latter case you will have to appoint a NS1 and NS2 name server, f.e. ns1.etechsupport.net, and ns2.etechsupport.net (a primary and a secondary name server).
In both cases, you will have to provide your domain registrar with at least two name server addresses to link to your domain. You will also have to add these DNS addresses to your TCP/IP stack on your server. If your ISP provides the DNS server you need to forward him any domain names which will reside on your server. Your ISP will then add the necessary MX records and A records to the DNS server.
If you want to receive e-mail from the Internet, you will need to have a Mail Exchange (MX) record for your domain in your ISPs or your own DNS database. An MX record has 3 parts: your domain name, the name of the machine that will accept mail for the domain, and a preference value. The preference value lets you build in a priority level, f.e. etech.net mail.etech.net 0. You can set multiple MX records, and the mail server will attempt the one with the lowest preference value first, and if it fails try the next, and so forth.
A records associate IP addresses with computer names. For example, an A record links the name 'yourdomain.com' to the IP address of your Web server.
DNS allows machines to have a true (canonical name), as well as an unlimited number of aliases. The CNAME record takes care of aliases. CNAME records can be useful when you want a subdomain to point to a computer outside of your domain.