Domain Name Server (DNS)

GCSE Internet Technologies (14-16 years)

  • An editable PowerPoint lesson presentation
  • Editable revision handouts
  • A glossary which covers the key terminologies of the module
  • Topic mindmaps for visualising the key concepts
  • Printable flashcards to help students engage active recall and confidence-based repetition
  • A quiz with accompanying answer key to test knowledge and understanding of the module

A-Level Internet technologies (16-18 years)

  • An editable PowerPoint lesson presentation
  • Editable revision handouts
  • A glossary which covers the key terminologies of the module
  • Topic mindmaps for visualising the key concepts
  • Printable flashcards to help students engage active recall and confidence-based repetition
  • A quiz with accompanying answer key to test knowledge and understanding of the module

Domain Name Server (DNS)

The DNS is a fundamental term of the internet. Mostly all the internet users are getting benefits from this application daily, but not each user is familiar with this terminology. DNS is a kind of digital directory that holds the names of and matches those names with numbers. Here we consider the internet protocol (IP) as numbers. IP’s are used as addresses for communication of devices connected with the internet. Devices connected to the internet that include smartphones, laptops, personal computers, and tablets have unique IP addresses. Therefore, it is a decentralized system used for matching the website names (URLs) and numerical addresses (IP) on the web of a specific website for which the client is requesting.

Domain Name Server (DNS) Image 1
Figure 1: DNS Significance

DNS History

In the initial stages of the internet, there were just a few devices, and the network was too small; therefore, correspondence among the people was only fluent and more effortless. Each computer was assigned with a specific IP address, but the system could not work for a long time. Over time, the number of devices became greater for connection with the network. Therefore, a standardized design was required for such a huge problem. The one solution was to directly enter the web page’s IP address where it resides in the server, but it was not easy to remember or record numerical data for each web page. It was more comfortable for the people to retain the domain name as the identity of the business. In the late 1970s, Elizabeth Feinler assigned the names and addresses and developed a master list of all the devices connected with the internet in a text file. The approach was not as much strength as the users and devices connected to the internet were proliferating. Paul Mockapetris proposed multiple suggestions to overcome this problem in 1983. He ignored the system of Feinler and maintained a new system that is known as DNS. The proposed methodology is changed now, as Mockapetris; the root level is still according to his perspective as 40 years have passed.

DNS Working

DNS, the whole working directory is not available at a single place somewhere on the internet. At the beginning of 2019, about 342 million registered domain names are impossible to maintain at one place as it holds a large amount of data indeed. As the internet network is spread worldwide, the same as the directory of domain names is distributed.

The domain name is a sort of interface that is easy to remember and map for humans like (www.kaggle.com), and the integrated IP address is (35.244.233.98). We can compare this term to a phone directory in the older age where all the phone numbers were listed. DNS performs functionality in the application layer protocol.

Domain Name Server (DNS) Image 2
Figure 2: DNS Functionality

Whenever a client types the URL in the browser bar, the query is first checked into the local cache. If the client’s address is not available in the cache, the browser will request the DNS server regarding kaggle.com IP address in the local area network (LAN). The server then shares the IP address with the browser to ask the Kaggle web host for data access. The web host then returns the required elements to maintain the home page in the local browser.

DNS Terminology

1. Domain Names:

A domain name is a string of easily readable words and understandable by the human-like Kaggle.com, Amazon.com, etc. Clients enter the domain name in the browser at the place of the URL field. The Internet Corporation manages the domain names for Assigned Names & Numbers (ICANN).

2. Top Level Domain (TLD):

The last portion of the URL is the top-level domain (TLD), including .com, .net, .org, etc. For the sake of an example (https://www.kaggle.com), here “.com” is TLD. TLDs for country codes are separate, which shows a specific location of the website. For instance (www.gov.uk) here, this website represents the data related to the United Kingdom. The Undermentioned are a few more examples of TLDs.

  • .com represents commercial or business websites.
  • .gov represents government agencies’ websites.
  • .edu represents the education institutes websites.
  • .org represents the (non-profit) organizational websites.
  • .mil represents military websites.
  • .net represents networking organization websites.
  • .eu represents the European Union websites
Domain Name Server (DNS) Image 3
Figure 3: Top Level Domain (TLD)

3. Second Level Domain:

The portion of the URL before TLD is known as the second-level domain. We can make this concept by an example, i.e. (www.kaggle.com) here, “Kaggle” is the second-level domain.

4. Sub Domain:

The subdomain in a URL is used to represent a specific area regarding which that website is.

Domain Name Server (DNS) Image 4
Figure 4: DNS Hierarchy

5. Name Server:

Just like a phone directory, the “name server” is a gathering of domain names that are being matched with the IP addresses.

DNS Record Types

1. A Record:

A Record is short of Address Record that maps the IP addresses with their domain names.

2. CNAME:

CNAME is short for Canonical Name Record that defines one place as an alias to another (routing all traffic to the Alias to the destination; the canonical address).

3. Alias:

Alas is the same as the CNAME record that is used to integrate one address to another. However, Alias is used for the coexistence of the same name with other records.

4. MX Record:

MX Record is the abbreviation for Mail Exchange Record, where records redirect the email domain to the servers used for hosting the domain of user accounts. MX Record is applied for evaluating the priority of the email servers for a domain.

DNS Types

Servers have two different types, where queries are submitted by the browser whenever a client requests to open a specific website in the browser. Both the forms of servers are listed and described below.

  1. Recursive DNS Servers
  2. Authoritative DNS Servers

Both the servers hold the canonical information to synthesize the IP address with the URL’s domain name.

Domain Name Server (DNS) Image 5
Figure 5: DNS Framework

1. Recursive DNS Server Working:

In the DNS lookup method, recursive servers are the workhorses. To appeal with the correct IP for the querying user, they always have to create multiple DNS lookups. Usually, these servers are operated by an ISP (Internet Service Provider) or specialized DNS resolution providers. E.g., Google retains its own public recursive DNS servers

2. Authoritative DNS Servers Working:

If someone holds a domain name, he may require using an Authoritative DNS server at any stage to link the domain name to an IP address. This is only performed on the DNS Authoritative list.

In a hierarchical system, authoritative DNS servers are installed. It all begins with servers with the dot root tag. These authoritative name servers, such as Top-Level Domains (TLD), know where to locate the next level that is fixed in the hierarchy. At the peak of the conceptual DNS, the tree is the root server. They precisely know the authoritative servers’ IP addresses are the ones managing Top Level Domains (TLD) DNS queries such as “.com”. Authoritative servers have direct access to the root name servers, whereas Recursive servers often have already processed or preserved the knowledge.

DNS Resolver

The first stop in the DNS lookup is the DNS resolver. DNS resolver is liable for communicating with the client who made the original request. The resolver begins the question sequence that eventually leads to converting a URL into the IP address needed.

Domain Name Server (DNS) Image 6
Figure 6: DNS Resolver

The difference between a recursive DNS question and a recursive DNS resolver is significant. The question refers to the request made to a DNS resolver, which allows the query to be resolved. The machine that accepts a recursive query and processes the answer by creating the required requests is a DNS recursive resolver.

DNS and IP Address:

More than one IP address will refer to each domain. Some websites contain multiple IP addresses that match a single domain name. For instance, the www.google.com server your computer reaches is likely to be entirely different from the server someone in another region would run by typing in their browser the same site name.

Another explanation for the dispersed existence of the directory is the length of time it might take while you were searching for a site to get an answer if there was just one place for the directory, shared with the millions, potentially billions of people who were all looking for data at the same moment. To use the phone book, that is one long line.

Efficiency by DNS:

In a hierarchy that helps keep stuff going fast and efficiently, DNS is structured. The initial search for the IP address is rendered to a recursive resolver. The recursive resolver understands which other DNS servers it has to query for its IP address to fix a site’s name (networkworld.com). This quest leads to a root server that knows all the top-level domain stuff, such as .com, .net, .org, and all the domains of those countries, such as .cn (China) and .uk (United Kingdom). Root servers are spread worldwide, but the device typically leads you geographically to the nearest one.

If the request hits the right root node, it heads to the top-level domain name server (TLD) that holds the second-level domain information, the terms used before you visit .com, .org, .net. The request is then submitted to the Domain Name Server, which contains the site and its IP address records. If the IP address is discovered, it is given back to the user, who will now access the website using it. All this takes milliseconds.

Since DNS has been operating for the past 30-plus years, most individuals take it for granted. While designing the device, the defense was still not noticed, but hackers took full advantage of this, generating a range of assaults.

Reflection Attacks:

With a massive volume of messages from DNS resolver servers, DNS reflection attacks will overwhelm clients. Attackers use the phishing IP address of the target to request huge. The client experiences a torrent of unrequested DNS data as the resolvers respond, which overwhelms their computers.

DNS Caching:

DNS information is exchanged across several servers to get around this problem. Yet data is often cached locally on client machines for places visited currently. Users probably use Google.com multiple times a day. Rather than your device querying the IP address of google.com from the DNS name server any time, the knowledge is retained on your device so that it doesn’t have to contact a DNS server to determine the IP address of the name. Moreover, caching can take place on the routers used to link clients to the internet and the ISP user servers. The number of requests that make it to DNS name servers is far less than it might sound, with too much caching.

Domain Name Server (DNS) Image 7
Figure 7: DNS Caching, Poisoning

Cache Poisoning:

Poisoning the DNS cache will divert visitors to harmful Web pages. Hackers attempt to inject fake address documents into the DNS, so the DNS reacts with the IP address of a separate domain, one managed by the intruder, when a possible target demands an address agreement for one of the poisoned pages. Victims will be fooled into surrendering passwords or ransomware updates while they are on these fake pages.

Resource Exhaustion:

The DNS networks of ISPs may be obstructed by DNS resource exhaustion assaults, preventing ISP consumers from accessing internet pages; this may be achieved by assailants declaring a domain name and employing the name server individual as the authoritative server of the domain. So, if a recursive resolver is unable to include the IP address associated with the domain name, the victim’s name server may be requested. Hackers create vast amounts of requests for their domain and launch into non-existent subsites, culminating in a flood of requests for the resolution being shot on the target’s name server, flooding it.

DNSSec:

DNSSec is a short form of DNS Security Extension, employed for secure communication in numerous layers of servers that come in DNS lookups. ICANN, the company responsible for the DNS scheme, devised it, familiar with weaknesses in communication among various levels of DNS.

Domain Name Server (DNS) Image 8
Figure 8: Comparison of with and without DNS-Sec

By making each level of DNS server digitally sign the requests, DNSSec will resolve this, ensuring that attackers do not command the requests received by end-users; this establishes a confidence chain. The request’s credibility is checked at – point of the search. 

DNS over HTTPS:

DNS is on the threshold of one of the most significant changes in its existence. Google Chrome and Mozilla Firefox are the most prevalent web browsers and hold the lion’s share in the world of browsers. Both the agencies are moving their steps towards DNS over HTTPS, where encrypted DNS is requested in HTTPS protocol.

Not through debate, it is a pass. Paul Vixie, who performed most of the initial studies on the DNS protocol earlier in the 1980s, considers the change a protection “disaster”: corporate IT, for example, would have a much stricter time controlling or guiding DoH traffic that crosses their network. Nonetheless, Chrome is universal, and DoH will shortly be turned on by default, but we’ll see what the future brings.

DNS Advantages:

  1. Typically, DNS is a unique system that assists the whole world to browse the internet. Therefore, it is mandatory to keep the DNS servers maintained as the internet is an integral part of our community.
  2. There is no need to remember each IP address for browsing the websites. DNS servers give a nifty solution for the conversion of domain names to addresses of the web. Imagine how it feels nasty to record or memorize each address for opening a web page.
  3. DNS provides enhanced security for the connected systems with the internet. Servers designed for security measures ensure that no malware can attack someone’s device. However, in larger organizations where data is in large amounts, special measures are required to secure tons of sensitive data from unauthorized hands.
  4. DNS servers provide a fast internet speed. Individuals and enterprises using DNS servers avail high-speed connection as a critical benefit.

 DNS Disadvantages:

  1. One of the DNS’s fundamental limitations is that only ICANN, a non-profit entity with origins connected to a single country, will manage the register; this contradicts the idea of net neutrality, and for the past three decades, it has become a commonly propagated point.
  2. Usually, DNS queries do not hold any details regarding the individuals who have initiated them; this is a crucial reason for the explanations for DNS’s success among hackers.
  3. DNS servers work on a slave-master concept; this suggests that if the master portal is disabled or corrupted in some manner, then the web page or archive that was hosted on the server would be impossible to reach. Hackers have also exploited this to their benefit. They have been able to find means of phishing details by attacking the server computer and allowing redirects to other sites.

Summary and Facts:

DNS is a naming system for computers, services, and specific devices that are connected with the internet. This naming technique is a decentralized approach that is hierarchical. DNS correlates the domain names allocated to each of the involved organizations with separate details. It converts more readily stored domain names to the numerical IP addresses required for computing networks and systems with the underlying network protocols to be found and recognized.

What do you mean by Domain Name Service (DNS)?

  • DNS is a kind of digital directory that holds the names of and matches those names with numbers.
  • IP’s are used as addresses for communication of devices connected with the internet.
  • It is a decentralized system used for matching the website names (URLs) and numerical addresses (IP) on the web of a specific website for which the client is requesting.

What do you know about DNS history?

  • In the late 1970s, Elizabeth Feinler assigned the names and addresses and developed a master list of all the devices connected with the internet in the form of a text file.
  • The approach was not as strong as the users and devices connected to the internet were overgrowing.
  • Paul Mockapetris proposed multiple suggestions to overcome this problem in 1983. He ignored the system of Feinler and maintained a new system that is known as DNS.
  • The proposed methodology of Paul Mockapetris is a bit changed now, but the root level is still according to his perspective as about 40 years have gone past.

How does DNS Work?

  • Whenever a client types the URL in the browser bar, the query is first checking into the local cache.
  • If the client’s address is not available in the cache, the browser will send a request to the DNS server regarding kaggle.com IP address in the local area network (LAN).
  • The server then shares the IP address with the browser to request the web host for data access.
  • The web host then returns the required elements to maintain the home page in the local browser.

What are the key terminologies used in the subject of the DNS?

  1. Domain Names
  2. Top-Level Domain (TLD)
  3. Second Level Domain
  4. Sub Domain
  5. Name Server

Name the record types in the DNS?

  1. A Record
  2. CNAME
  3. Alias
  4. MX Record

Name the significant two types used in the DNS subject?

  1. Recursive DNS Servers
  2. Authoritative DNS Servers

Define the critical advantages of DNS?

  1. DNS is a unique system that assists the whole world to browse the internet.
  2. There is no need to remember every IP address for browsing the websites.
  3. DNS provides enhanced security for the connected systems with the internet.
  4. DNS servers provide a fast internet speed.

Enlist the significant disadvantages of DNS?

  1. Only ICANN, a non-profit entity, will manage the register.
  2. Usually, popular hackers as DNS queries do not hold any details regarding the individuals who have initiated them.
  3. DNS servers work on a slave-master concept.

References:

  1. https://www.networkworld.com/article/3268449/what-is-dns-and-how-does-it-work.html
  2. https://www.verisign.com/en_US/website-presence/online/how-dns-works/index.xhtml
  3. https://www.cloudflare.com/learning/dns/what-is-dns/
  4. https://cloudacademy.com/blog/how-dns-works/
  5. https://dnsmadeeasyblog.medium.com/authoritative-vs-recursive-dns-servers-whats-the-difference-d0e5821c7617
  6. https://tutorialspoint.dev/image/DNS_Spoofing.png
  7. https://www.thesslstore.com/blog/wp-content/uploads/2018/10/DNS.jpg
  8. https://1.bp.blogspot.com/-EzzBK53if5I/XVYwgW2jSSI/AAAAAAAAQB4/VaG8_EHKtUUP6mGSVeUvfHbk1nUMJB8jACLcBGAs/s1600/doh_c2.png
  9. https://en.wikipedia.org/wiki/Domain_Name_System
  10. https://www.technology.org/2019/05/02/dns-servers-what-are-they-and-why-are-they-beneficial/
  11. https://tinydns.org/advantages-and-disadvantages/

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