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Some DNS basics
Once you have your domain registered, you will need to specify two or more name servers that is the authoritative servers for your domain name. Your authoritative DNS servers will hold information about your domain (known as zones). Some of these will be information like the IP address of your web server and mail server.
Your authoritative DNS servers for your zone (your domain) is either provide by your registrar or your web hosting company. It holds DNS name to IP address records and vice versa (e.g. www.netdummy.net è 203.117.178.18) and respond when it is queried for the information.
Unless you are hosting the DNS servers in your own local network, you should not have to worry too much about technicalities of setting it up correctly. Most web hosting companies and registrar that holds your DNS information will provide a web interface for you easily add and remove records for your domain on their DNS servers.
In a simplified scenario, when a query is made in regards to a domain, for example if you type a URL www.netdummy.net, your browser will request the IP address of www.netdummy.net through your ISP’s DNS servers which in turn will check it own cache for the IP address for www.netdummy.net. If that information is not available, it will then query the various root servers for location of the authoritative DNS servers for netdummy.net.
Once the IP address of the DNS server is obtained, it will then send another queries to the DNS server of netdummy.net for the IP address of www for zone netdummy.net. When all these information are obtained, your browser will connect to port 80 of the destination IP address that is resolved.
For emails, it will be a similar scenario except that the DNS will request the MX records for your Internet domain. You can have more than one MX record and it is prioritize based on a numeric value. A MX record with a value of 10 will be given higher priority over a value of 11, 20 or more.
As your mail client is only responsible for delivering the mails to your ISP’s server, it is your ISP’s mail server will do the resolving of IP address for mails for a particular domain in the background.
Again, once it is resolved, they will connect to port 25 of the destination IP address and attempt to deliver the mails. If the connection fails for any particular reason, your ISP’s server will attempt to connect to the next MX record’s address for delivery. This will continue until the number tries are exhausted or no further record could be processed.
You can test it by starting a command prompt (Click Start, Run, type CMD) and at the prompt type ‘telnet yourdomain.com 25'. You should get a server response and a prompt. Type quit, and then exit by typing exit at dos prompt once tested OK.
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