Networks

DNS

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DNS (Domain Name System/Servers) is merely an address book for the Internet, which keeps a list of all available IP addresses. Before DNS, a plain text computer file: “hosts,” was used to map hostnames to IP addresses. The “hosts” file can still be used as an alternative name resolution method; however, using DNS is far easier. Having to remember or look up IP addresses such as 171.34.21.11 would be difficult. With DNS, a user can instead just input the hostname of the website, such as “google.com” and automatically go to the correct IP address. All service records are controlled within DNS for the domain controllers (DC). When a client desires to search a service which is related to Active Directory, it calls the DNS to check the availability of the service. So without DNS, the Active Directory would not work correctly; it won’t let the user promote a DC if they are not interested in installing DNS. This promotion process will install the DNS on the DC when the user is promoting; also, the user will not have to configure anything.
Another advantage of DNS is that it supports parsing of the “hosts” file. The effect of multiple answers in the “hosts” file is also achieved by the presence of the DNS. Fallback from preferred to alternative DNS servers is also managed by the DNS.  Due to these reasons, a user cannot run a system without DNS. Many applications commonly used, use DNS services, such as E-mail, the World Wide Web, and instant messaging services. When it comes to E-mail, servers can require more information than the basic hostname and IP addresses. E-mails can be sent directly to the desired target domain or another E-mail server that is not the final destination. Because of this, DNS is needed to recognize and manage this information. While it takes time to resolve the information DNS manages (called overhead), DNS is handy and necessary for the correct operation of many applications. Thanks to DNS, users can navigate to websites and use applications such as E-mail servers with ease.
Reference:
Brain, Marshall. Crawford, Stephanie. (2001). How Domain Name Servers Work. Retrieved from https://computer.howstuffworks.com/dns1.htm.

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