Inserting Records Into The DNS Database
You know how records are retrieved from the DNS database. However, you would like to know how records get into the database in the first place. Let’s see how this is done in the context of a specific example.
Suppose you have just created an exciting new startup company called Network Utopia. The first thing you’ll surely want to do is register the domain name networkutopia.com at a registrar. A registrar is a commercial entity that verifies the uniqueness of the domain name, enters the domain name into the DNS database (you’ll see below), and collects a small fee from you for its services. Prior to 1999, a single registrar Network Solutions, had a monopoly on domain registration for com, net and org domains. But now there are many registrars competing for customers, and the Internet Corporation for Assigned Names and Numbers (ICANN) accredits the various registrars. A complete list of accredited registrars is available at http://www.internic.net.
When you register the domain name networkutopia.com with some registrar, you also need to provide the registrar with the names and IP addresses of your primary and secondary authoritative DNS servers. Suppose the names and IP addresses are dns1.networkutopia.com, dns2.networkutopia.com, 22.214.171.124, and 126.96.36.199.For each of these two authoritative DNS servers, the registrar would then make sure that a Types NS and a Type A record are entered into the TLD com servers. Specifically, for the primary authoritative server for networkutopia.com, the registrar would insert the following two resource records into the DNS system:
(networkutopia.com, dns1.networkutopia.com, NS)
(dns1.networkutopia.com, 188.8.131.52, A)
You’ll also have to make sure that the Type A resource record for your Web server www.networkutopia.com and the Type MX resource record for your mail server mail.networkutopia.com are entered into your authoritative DNS servers. (Until recently, the contents of each DNS servers were configured statically, for example, from a configuration file created by a system manager.
More recently, an UPDATE option has been added to the DNS protocol to allow data to be dynamically added or deleted from the database vis DNS messages.[RFC 2136] and [RFC 3007] specify the dynamic updates.
Once all these steps are completed, people will be able to visit your web site and send e-mail to the employees at your company. Let’s conclude our discussion of DNS by verifying that this statement is true. This verification also helps to solidify what we have learned about DNS. Suppose Alice in Australia wants to view the web pages www.networkutopia.com. As discussed earlier, her host will first send a DNS query to her local DNS server. The local DNS server will then contact a TLD com server. (The local DNS server will also have to contact a root DNS server if the address of a TLD com server is not cached). This TLD server contains the Type NS and Type A resource records listed above, because the registrar had these resource records inserted into all the TLD com servers. The TLD com server sends a reply to Alice’s local DNS server, with the reply containing the two resource records. The local DNS server then sends a DNS query to 184.108.40.206, asking for the Type A record corresponding to www.networkutopia.com. This record provides the IP address of the desired Web server, say, 220.127.116.11. which the local DNS server passes back to Alice’s host. Alice’s browser can now initiate a TCP connection to the host 18.104.22.168 and send an HTTP request over the connection.