DNS Lookups

Every computer is assigned its own IP address in the Internet. The IP address is like an ID code or a bank account number. It follows this format: 12.3.456.789. Every time a user visits a certain website, the DNS (Domain Name System) acts as the directory of all the corresponding IP addresses of domain names. When users enter a link to a website (e.g. www.ilovedebating.com), they usually type in the domain names because it’s easier to recall them than the IP addresses. The DNS server returns the IP address corresponding to the domain name.

Since thhe Internet is a huge and indefinite arena, a single DNS server cannot be expected to record all domain names and addresses accurately. Moreover, domains are sometimes moved to other machines resulting to a change of IP addresses. To address this problem, the DNS comes up with a hierarchy of machines or units, giving a higher ranking those that don’t change IP addresses often.

To resolve a domain problem, the following process should be done:

1. Type a website link in the address bar and press enter/return.

2. Right after pressing return, the browser will send a request to the DNS server in the network settings and ask for the corresponding IP address for the website link. The settings for these are usually configured automatically.

3. The ISP DNS server will now tap its look-ups cache and check how it can respond to the request. If it knows the answer to the question, the DNS is finished with the look-up. If it doesn’t, it carries on to Step 4.

4. If the ISP DNS server is unable to find a corresponding web address in its look-ups cache, it will re-check the domains it is responsible for and attempt to find matches. If it is able to do so, it sends the answer back. If it still cannot find a result, it moves on to Step 5.

5. A query will now be sent to the root of the DNS servers. These “roots” are found at the topmost part of the hierarchy. These roots contain the top-level domains such as .com, .edu, .net, and .gov. The root server will check the zone and will run a search for the website. After this, it delivers the NS record back to the DNS server. The IP addresses usually contain the NS record, so the browser can now return with the result of the request.

For country-specific domains such as .ph (for Philippines) or .uk (for United Kingdom), the root servers at the country level are the ones to coordinate with the ISP DNS. The result is acquired only through an extra look-up in the ISP DNS. It is only when the IP addresses are not found within the hierarchical system that the country-level root servers are tapped.

A DNS server should not be confused with a caching DNS server. The latter performs the look-ups by itself while the former only forwards the requests.