DNS lookup is the process of obtaining an IP address when a DNS resolution request is made. It can travel laterally through the DNS system or be forwarded to ascending or root servers. DNS lookups are used for network tools, email tools, web search, and network security.
A Domain Name System (DNS) lookup is the process of obtaining an Internet Protocol (IP) address when a DNS resolution request is made. They can also be the steps taken to resolve an IP address when a reverse DNS lookup is requested. The DNS system is an interconnected network of computer servers arranged in a hierarchy of domains and subdomains. Depending on the nature of DNS resolution and what DNS information is cached by DNS servers, a DNS lookup can travel laterally through the DNS system or be forwarded to ascending or root servers. The response to a resolution request will eventually be returned to the computer or network device that initiated the DNS lookup.
Network devices, including computers, usually have a local file called the hosts file, which will be looked at first when a DNS lookup is initiated. This file is kept in permanent storage and contains static entries of IP addresses associated with machine or domain names. If the searched name or IP address is not found in this file, a network device will contact the local DNS server, statically or dynamically configured in the network adapter configuration file. This is typically a DNS server that belongs to an Internet Service Provider (ISP) or corporate network.
If the local DNS server can resolve the DNS resolution request, it will send a DNS resolution response to the network device that initiated the DNS lookup. Depending on information cached by a local DNS server, it may forward the request. The local DNS server will eventually receive a response, cache the information received, and reply to the DNS lookup initiator with the requested information. A lateral request is usually initiated when the local server knows how to contact the DNS server responsible for a requested domain but doesn’t know how to reach a subdomain or a particular machine within a domain.
When a local DNS server doesn’t have any information, it will send a request up through the DNS hierarchy to a root DNS server. DNS servers ascending in the hierarchy typically behave the same way as local DNS servers. They will respond to or forward requests and store information as needed. If a domain or machine being looked up within a domain does not exist or cannot be contacted, the DNS server responsible for this information will send a reply back stating that the DNS lookup was unable to resolve the resolution request.
DNS lookups are often used with network tools, email tools, during a web search, and for network security. A DNS lookup is an integral part of the concept of ease of use, as it helps ensure that people can easily navigate the Internet by using names for resources instead of unintelligible IP addresses. DNS lookup works in the background, so it also helps ensure ease of use by hiding technical network details.
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