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Application Layer – Domain Name System (Dns Internet Working Overview)? The 20 Detailed Answer

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An application layer protocol defines how the application processes running on different systems, pass the messages to each other. DNS stands for Domain Name System. DNS is a directory service that provides a mapping between the name of a host on the network and its numerical address.The domain name system (DNS) is a naming database in which internet domain names are located and translated into Internet Protocol (IP) addresses. The domain name system maps the name people use to locate a website to the IP address that a computer uses to locate that website.DNS is a distributed database implemented in a hierarchy of name servers. It is an application layer protocol for message exchange between clients and servers.

How a DNS Server (Domain Name System) works.

How a DNS Server (Domain Name System) works.
How a DNS Server (Domain Name System) works.

Images related to the topicHow a DNS Server (Domain Name System) works.

How A Dns Server (Domain Name System) Works.
How A Dns Server (Domain Name System) Works.

Spoiler: This post is long but fun! We have seen the different layers present in the TCP/IP reference model and the different types of addressing methods implemented in all network transport models. Now that we have enough of the basics, it’s time to explore what each layer really does. So let’s start with the application layer first. The application layer proves services to end users, and most of the interesting applications rese in this particular layer. The other layers that exist below this layer mainly help to facilitate the user to use the various applications that exist in this layer. The three most important services that the application layer proves for the normal operation of various applications are: Network security. Domain Name Service (DNS). Network management. So, in this article, we mainly focus on the application layer domain name system. Before we go any further, let’s take a look at some common error messages we usually see when browsing the web. After reading this post, hopefully you can find a solution to your problem (root cause).

Domain Name System


Domain Name System

We’ve seen client-server network configuration. Therefore, the Domain Name System is also one of the supporting programs for client-server networking. It handles Internet addressing and naming. Users of email programs can know the recipient’s email address, but the IP protocol (of the TCP/IP model) requires an IP address. DNS client programs send requests to domain name servers to map email addresses to corresponding IP addresses. It is also important to understand that every remote device (host on the network) has an alias. To entify an entity, the TCP/IP protocol uses an IP address, which uniquely entifies a host (any remote device) connection to the Internet. However, people prefer to use names rather than numerical addresses (for simplicity). So we need a system that can map names to addresses or addresses to names. This entity is called DNS (Domain Name System). End users do not use this service directly, there is an application that does this mapping (aliases and IP addresses).

So how does Domain Name System(DNS)  really works ?

There should initially be an application that maps aliases to their IP addresses (which are then used by the TCP/IP protocol). For this mapping, the application calls a library procedure called a parser. Aliases are passed as arguments to the parser. The resolver then sends a UDP packet to the local DNS server, which looks up the name and returns the corresponding IP address to the resolver. The resolver then sends this address to the caller. The program can then establish a TCP connection with the target or send UDP packets. The alias

Name Space in DNS

assigned to each remote host on the network should be carefully chosen from the namespace. In other words, each name must be unique so that it can be associated with each unique IP address. The namespace that maps each address to a unique name can be organized in two ways: Flat. Structured.

Flat Name Space 

Each address has a name. It has no structure, just a string. The main disadvantage of a quorum namespace is that it cannot be used in a large system like the Internet, as it must be centrally controlled to avo ambiguity and duplication.

Hierarchical Name Space In DNS !!

Each name consists of many parts (in short, there is a well-defined structure to ensure uniqueness). The first part can correspond to the organization type, the second part can define the company name, the third part is the department name, etc. The part that defines the type of institution is assigned by the central institution. The decision of further name design can be left to the company itself. An institute can add any prefix or suffix to its name to define its host or resource. The central authority can only control part of the name, not the full name.

Domain Name Space

Basically, the Internet has been dived into many top-level domains. Each domain consists of many hosts. In order to have hierarchical namespaces, domain namespaces are designed. In this design, names are basically defined in an inverted tree structure with the root at the top. This tree can only have 128 levels, ie. H. Level 0 (root) to level 127. There are two types of top-level domains, generic and country.

Generic domains

Generic domains can be of different types such as com (commercial), edu (educational), gov (government), int (international organizations), mil (military), net (network provers), and org (nonprofit organizations) ). The country field usually contains an entry for each country. Also, each domain is named by following the upward path. A fully qualified domain name is a sequence of labels separated by periods (.), for example: Fully qualified domain names always end with a null tag, which means the last character is a period, since an empty string is nothing. This is called hierarchical naming. Each node in the


tree has a label, which can be specified with 63 characters. We have a hard time remembering the order of numbers (IP addresses), and that’s where domain names come in. Now let’s take some examples: , , are some domain names. Here, the com and uk portions of these domain names are referred to as top-level domains. There are many other top-level domains, including com, edu, gov, mil, net, org, int, and two-letter combinations that are unique to each country. Therefore, each “com” top-level domain must be unique. The leftmost word, www or encarta, is the hostname. It specifies the name of a specific computer (with a specific IP address) in the domain. Therefore, each domain can contain millions of hostnames, as long as they are all unique. Note: Domain names are not case sensitive; H. edu and EDU are the same. Component names can be up to 63 characters long. To create a new domain, we need to get permission from the domain we want it to contain. The

What is a Domain?  

domain is usually a subtree of the domain namespace. The name of each domain is the domain name of the top node of the subtree. A domain can be further dived into subdomains.

Distribution of Name Space

must store the information contained in each namespace. However, having only one computer storing such a large amount of information is very inefficient and unreliable. The failure of a single computer can render data inaccessible.

Hierarchy of Name Servers

A simple solution to these problems is to distribute information across multiple computers called DNS servers. One way to achieve this is to dive the entire space into many domains based on the first level. Nameservers contain DNS databases, ie. H. Different names and their corresponding IP addresses. In other words, we leave the root alone and create as many domains (subtrees) as there are first-level nodes. Since domains created in this way can be very large, DNS allows the domain to be further subdived into smaller domains (subdomains). First-level domains are further subdived into smaller sub-domains called second-level domains. The hierarchy of servers is the same as the hierarchy of names. Zone: We need to define the zone each server has permissions to. This restricted area to which a specific server has access is called a zone. The server creates a database called a zone file and stores all the information for each node under the domain. However, when a server dives its domain into subdomains and delegates some of its authority to other servers, domain and zone refer to different things. The information for the nodes in the subdomain is still stored in the lower level servers, and the origin server keeps some kind of reference to those lower level servers. Root Server: This designated zone consists of the entire DNS tree. It only keeps references to those servers. There are multiple root servers, each covering the entire namespace. Servers are distributed all over the world. DNS defines two types of servers, primary and secondary. Master server: This type of server stores files in its zone. He has the right to create, update and delete any zone file and save it to the local disk. Secondary server: This server transfers complete information about the zone from another server (which can be primary or secondary). The transmitted information is then stored in disk storage. It does not have permission to create and update zone files.

What Is DNS in the Internet ?

Now we will understand how DNS is implemented on the Internet. On the Internet, the domain name space (tree) is dived into three distinct areas: general domains, country domains, and reverse domains. 1. Generic Domain The first level of the Generic Domain section allows 14 possible values. Generic domains define registered hosts according to their generic behavior. For example we have edu for education etc. museums museum and other non-profit organization names personal name (indivual) network support center org non-profit organization pro personal professional organization second country domain This domain uses a two letter country abbreviation such as B. United States for the United States. The second label in this area gives the organization or country name. 3. Inverse domain This is used to map addresses to names. This happens, for example, when the server receives a request from a client to complete a task. Although the server has a file containing a list of authorized clients, only the IP addresses of the clients (extracted from the received IP packets) are listed. The server then asks its resolver to send a query to the DNS server to match the address with the name to see if the client is on the authorized list. This is the exact opposite of the name-to-address mapping process discussed earlier.

Name Address Resolution:

The process of mapping names to addresses and vice versa is called name-address resolution. What is a resolver in DNS? DNS applications are based on a client-server model. To map a name to an address in DNS (and vice versa), a DNS client called resolver needs to be invoked. The resolver then sends a map request to the nearest DNS server and accesses its memory. If the server for this request has no information, it will either forward the resolver to another server or ask another server to prove the required information. So the parser finally gets the map from the source, then checks for errors, and if found healthy, delivers the map to the requesting process (host). Mapping names to addresses: First, the resolver passes the host name to the server and requests the corresponding IP address. The server then checks the generic or country domain for the desired address. If the local DNS server doesn’t have an answer, it points the resolver to another server. Country domains use the same method.

Mapping addresses to names:

Now the client sends the server the IP address and requests its name. This type of query is called a PTR (pointer) query. To answer this type of query, DNS uses reverse domains. However, in the request, the IP address is reversed, and the two labels in-addr and arpa are appended to create a domain that can be used in the reverse domain part. For example, if the resolver receives the IP address, the resolver first reverses the address, then adds two labels, before sending. The domain name sent is “”. Received and resolved by local DNS. Recursive Resolution Clients (resolvers) can simply request recursive responses from name servers. This means that the parser expects the server to prove the final answer. If the server is authoritative for the domain name, it checks its database and responds. If the server is not an authorization server, it will send the request to another server (usually the parent server) and wait for its response. If the parent is authoritative, it responds, otherwise it sends the request to another server. Iterative resolution In this case, if the server has authority on the name, it sends a response. But if it doesn’t have an answer, it sends the client the IP address containing the server that requested the answer. If the newly addressed server solves the problem, the request is responded to with the IP address, otherwise the IP address of the new server is returned to the client. Now the client has to repeat the request to the third server. This process is called iterative solution.

DNS Message Format

DNS has the following two types of messages, then they both have the same query format. answer or answer. Both query and response messages have the same header format, with some fields of the query message set to empty. The header is 12 bytes long, and the client uses the entifier subfield to match the response to the request.

What is Caching in DNS ?

Whenever the server receives a request for a name not in its domain, it searches its database for the server IP address. Reducing this search time will improve efficiency. DNS handles this using a mechanism called caching. When a server requests a map from another server and then receives a response, it must store that information in its cache before sending it to the client. If the same or another client requests the same image again, they can check their cache and fix the problem in less time. In my next article, we’ll see the next interesting application in the application layer soon. So stay tuned. report this ad

What is the DNS Domain Name System and how is working?

The domain name system (DNS) is a naming database in which internet domain names are located and translated into Internet Protocol (IP) addresses. The domain name system maps the name people use to locate a website to the IP address that a computer uses to locate that website.

What is DNS in application layer?

DNS is a distributed database implemented in a hierarchy of name servers. It is an application layer protocol for message exchange between clients and servers.

What is DNS and how it works step by step?

The Internet’s DNS system works much like a phone book by managing the mapping between names and numbers. DNS servers translate requests for names into IP addresses, controlling which server an end user will reach when they type a domain name into their web browser. These requests are called queries.

Does DNS run at application layer?

The Domain Name System (DNS) is an application layer system that provides mapping between domain names and the associated IP addresses. DNS is described in detail elsewhere [123, 124]. DNS is widely used in the Internet, as practically all Web addresses and email addresses contain domain names.

What is DNS in Internet?

The Domain Name System (DNS) turns domain names into IP addresses, which browsers use to load internet pages. Every device connected to the internet has its own IP address, which is used by other devices to locate the device.

What is DNS explain with example?

(Domain Name System) The Internet’s system for converting alphabetic names into numeric IP addresses. For example, when a Web address (URL) is typed into a browser, DNS servers return the IP address of the Web server associated with that name.

How do domain names work?

Domain names are just like a contact in your phone. Rather than typing a complicated set of numbers (the IP address) into your browser, you type in a domain name. That domain name is human-friendly and much easier to remember than an IP address. All domain names are connected to a unique IP address.

Why do we need the Domain Name System DNS?

Question: Why do we need DNS (Domain Name Server)?

It allows you to use internet more easily by allowing you to specify a meaningful name on your web browser instead of using IP address.

How many types of DNS are there?

There are three main kinds of DNS Servers — primary servers, secondary servers, and caching servers.

What are the 3 types of DNS queries?

There are three types of queries in the DNS system:
  • Recursive Query. …
  • Iterative Query. …
  • Non-Recursive Query. …
  • DNS Resolver. …
  • DNS Root Server. …
  • Authoritative DNS Server.

What is DNS in Active Directory?

Active Directory Domain Services (AD DS) uses Domain Name System (DNS) name resolution services to make it possible for clients to locate domain controllers and for the domain controllers that host the directory service to communicate with each other.

How do DNS queries work?

In general, the DNS query process occurs in two parts:
  1. A name query begins at a client computer and is passed to a resolver, the DNS Client service, for resolution.
  2. When the query cannot be resolved locally, DNS servers can be queried as needed to resolve the name.

Is DNS a layer 3 or 4?

In OSI stack terms, DNS runs in parallel to HTTP in the Application Layer (layer 7).

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