DNS stands for “Domain Name System”, which is a massive directory distributed across the world. In other words, DNS serves the purpose of the phonebook for the internet. It functions so instantaneously and seamlessly that we don’t realize how much we use it every day.
We can understand DNS through a basic analogy. In a phonebook, we usually type a name whose number we need to check, we need not memorize the person’s contact number. The same service is provided by a DNS. Every device connected across the internet has a unique IP address. This IP address is used by the machines to interact with each other. Domain names are human-readable names that we enter into a web browser to access a website. Domain names are analogous to the names in the phonebook, while the IP address is the corresponding contact number. Computers interact through IP addresses which are complex strings of alphanumeric characters. Basically, DNS translates domain names to corresponding IP addresses to identify the different computers across the world. There can be more than one IP address associated with a domain name.
Around thirty years back, when the internet was introduced, people needed to memorize the IP address of the website that they wanted to visit. Computers being digital machines were able to communicate only through numbers. As the internet age began, the number of websites started to grow from hundreds to tens of thousands. The increasing number of IP addresses made it difficult for people to memorize. Paul Mockapetris in early 1980s introduced a system that was able to automatically map the domain names to its corresponding IP addresses. This led to the birth of the DNS which serves as a backbone of Internet till today.
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There are mainly 2 types of queries:
The basic function of a DNS is to convert the user-friendly domain name into a corresponding computer-friendly IP address. Let’s look at the various steps:
To understand this even better, we must have a precise knowledge of domain name and IP address. An Internet Protocol address (IP address) is a unique numeric address that is accredited to every single device that uses an Internet Protocol-based network. Basically, with the help of an IP address, devices recognise each other on a network. A simple example of an IP address is 126.96.36.199.
A domain name is an understandable way of identifying entities on a network; any particular website can be accessed by a domain name. For example, Microsoft is the domain for the website microsoft.com.
Every domain name has one or more than one IP addresses assigned to it. DNS matches the domain name with the IP address accredited to it and fetches the right webpage for the user. For a user, it is more convenient to remember a domain name than an IP address but the computer understands only in binary numbers hence the DNS transcripts the domain into IP addresses with the help of DNS servers.
A DNS server is a vast storehouse of domain names and their relevant IP addresses and helps to retrieve the IP addresses from the domain name or the hostname. We can deduce that the DNS server is the major element that incorporates the DNS protocol and serves the Web Hosts and clients on an IP based network. It bridges the gap between the humans and the computers.
There are two basic types of DNS servers: Primary and Secondary servers.
A primary server is responsible for the administration of the domain and it gets its information directly from the local files. It hosts the controlling zone file whereas Secondary servers get their information from a primary server in communication known as a zone transfer and contain read-only copies of the zone file.
The Domain Name System is organised in a hierarchy with different managing areas also known as zones and root servers are at the top of this hierarchy. Thirteen root servers are used to query the different root server networks. These are arranged in alphabetical order from A to M, the first 13 letters of the alphabet.
A DNS query without any caching is solved by the help of mainly four servers which are recursive resolvers, root nameservers, TLD nameservers, and authoritative nameservers. The query from the client is received by the DNS resolver which then looks up the IP address. The resolver then itself starts enacting as a client and then asks the rest three servers to fetch the correct IP address.
First, the root server converts the domain into IP address and responds the resolver with the Top Level Domain servers that stores all the details of the domain servers. Now the TLD responds to the resolver with the IP address of the domain’s authoritative nameserver. The authoritative nameserver responds with the IP address of the origin server on the query of the recursor.
Finally the resolver sends the origin server IP address to the client and in turn, the client can directly resolve its query with the origin server.
Cached data can also be used to resolve DNS queries apart from the above process used by the recursor. Once an IP address is obtained for the website, it can be saved as a cache for about 24 hours so that meanwhile any other user requests for the same IP address, it can be directly retrieved from the cache thus avoiding all the hassle. But after 24 hours, the resolver has to create a new cache.
DNS server could fail due to varied reasons such as:
Earlier DNS server outage had a significant impact on the business but today due to server monitoring TLD nameservers, root DNS servers and backup recursive, it has become more efficient in resolving the issues. Though most of the outage and failure may be solved, one must have a DNS failover implemented so that if there are any DNS server outage, one can very easily be transferred to another DNS server without the knowledge of the end-user.
These are the few precautions that can help you mitigate the effects of an attack. Some of these are:
Internet Corporation for Assigned Names and Numbers (ICANN), the organization in charge of the DNS system invented DNS Security Extensions to secure and ease up the interaction between the various levels of servers during lookup. DNSSEC devised a system where each level of DNS server digitally sign its requests, which makes it certain that the requests sent in by end-users aren’t appropriated by attackers. Moreover, DNSSec can verify whether a domain name exists and if it doesn’t then it protects the client and the servers from the infiltrated domain.
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