Domain Name System (DNS)

The Domain Name System (DNS) is the phonebook of the Internet. Domain names like uninets.com are used by people to access information online. In digital communications, only binary numbers are in use either Web browsers communicate with, or packet forms by using source or destination IP. For browsers to load Internet resources, DNS(domain name system) converts domain names to IP addresses.

History Of DNS (Host Files)

Before DNS days there were host files, which reside in a centralized location, and everyone needed to download from there. Almost every operating system uses these hosts file to map hostnames (human-friendly) to numerical Internet Protocol (IP) addresses. Even in today’s world as well you may find them. Although not required to make changes to that it is quite feasible to amend local DNS(domain name system).

It contains lines of text for an IP address field followed by host names; the hash character (#) specifies the comments; blank lines in the file are ignored. Below is the host file path for the Windows system –

Limitations for using such a resource were it is flat in structure and requires manual entries each time.

FQDN is the complete domain name either for a specific computer, or host on the internet. The FQDN consists of two parts: the hostname and the domain name. For example, an FQDN for the uninets mail server might be [email protected] The hostname is info, and the host is located within the domain uninets.com can be one of the hostnames.

DNS uses distributed database system hierarchy to manage its resources.? It is an inverted tree structure, much like directory.

The DNS(domain name system)tree has a single domain at the top of the structure called the root domain. A period or dot (.) is the designation for the root domain. Below the root domain are the top-level domains that divide the DNS hierarchy into segments. This root server is not installed on a single server but on multiple hardware at different locations.

This is distributed model as any authorities can be distributed.

A domain is a label of a DNS tree. On the DNS tree, each node stands in for a domain. Individual businesses or other entities are represented by domains below the top-level domains. To make managing the host machines for an organization’s ease, these domains can be further separated into subdomains.

To make it easier to remember IP addresses, ARPANET developed the idea of TLDs in the 1960s.

Under the direction of the Internet Corporation for Assigned Names and Numbers, each top-level domain has a separate registry that is run by a specified organization (ICANN).

Internet Corporation for Assigned Names and Numbers categories TLD into different types –

1. Generic Top-level Domains (known as gTLD commonly, which are the most popular types of domains, containing three or more characters, and anyone can do the registration. Like .com and .org.)

.com – for commercial sites

.org – for organizations

.net – for networks

.info – for information platforms

.biz – for businesses

1. Sponsored Top-level Domains or sTLD (supervised by private organizations, unlike with gTLDs, the sponsored top-level domain list only includes a small, limited number of options)

.edu – for higher educational institutions

.gov – for United States governmental agencies

.cat – for Catalan linguistic and cultural community

.museum – for museum organizations

.travel – for travel industry businesses

1. Country Code Top-level Domains or ccTLD (There are 312 country code top-level domains established for specific countries and territories, identifying them with a two-letter string. Some of the most well-known ccTLD include)

.us – for the United States

.fr – for France

.it – for Italy

.in – for India

.br – for Brazil

1. Infrastructure Top-Level Domain or ARPA (This special category contains only one TLD: the Address and Routing Parameter Area (ARPA). The. arpa domain extension is managed directly by the IANA)
2. Test Top-Level Domains or TLD (These are reserved for documentation purposes and local testing and cannot be installed into the root zone of the DNS).

The authoritative DNS server is the final holder of the IP for the asked domain. When you write a domain name in your browser, a DNS(domain name system) query is sent to your internet service provider (ISP). The ISP has a recursive server, which might have the needed information cached in its memory. But if the data is outdated, this recursive server needs to find the IP elsewhere. It will try to find it in other recursive servers, but if it cannot, it needs to get the IP address from an authoritative DNS server. Such a server is the name server, which has the original zone records.

These DNS servers are giving responses to queries just for the zones they are configured. This makes them very efficient and fast.

There are two types of authoritative servers: master (primary) and secondary (slave). Each zone must have only one master name server, and it should have at least one secondary name server for backup purposes to minimize dependency on a particular node. The zone data updates and maintenance are reflected in the master’s name server and the changes are then reflected in secondary name servers. Both master and secondary name servers are authoritative for a zone.

Non-Authoritative

Non-authoritative name servers do not contain the original zone files. They may have a cache with previously requested DNS records from all the DNS lookups done previously. If a DNS server responded to a DNS query that does not have the zone file, it is a non-authoritative answer.

to find names from numbers, using a process commonly called reverse name resolution.

DNS Cache

It is a mechanism in place to help reduce the frequency at which a website visitor’s browser must request a complete DNS lookup.

It is a temporary storage of information about previous DNS lookups on a machine’s OS or web browser. Keeping a local copy of a DNS lookup allows your OS or browser to quickly retrieve it and thus a website’s URL can be resolved to its corresponding IP much more efficiently.

During a new DNS(domain name system) lookup, the lookup passes through the resolver, root server, and TLD server. At each step, information is gathered and cached for later use. Therefore, even if the local DNS cache is empty, the resolver may have a cached copy of the required information thus, avoiding the need to go through the complete DNS(domain name system) lookup process.

Checking your DNS cache on Windows – open your command prompt and enter the following command: ip config /display DNS. The method used to flush your DNS cache is ip config/flush DNS

DNS TTL

TTL (time to live) is a setting that tells the DNS resolver how long to cache a query before requesting a new one. The information gathered is then stored in the cache of the recursive or local resolver for the TTL before it reaches back out to collect new, updated details.

For example, if the DNS TTL is set to 1800 seconds (30 mins), the resolver will have to regather the details around a website every 30 minutes. If 100 users visit the site in that period, they will all see the same thing, until the resolvers update their TTL.

We also offer a diverse library of pre-recorded videos for any online training or buy self-paced courses.