IP Address Forward and Reverse DNS Lookup

URLs and IP addresses are two sides of the same coin

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In networking, IP address lookup refers to the process of translating between IP addresses and internet domain names. Forward IP address lookup converts an internet name to an IP address. Reverse IP address lookup converts the IP address number to the name. For the vast majority of computer users, this process occurs behind the scenes.

What Is an IP Address?

An internet protocol address (IP address) is a unique number assigned to a computing device such as a computer, smartphone, and tablet to identify it on a network.

IPv4 addresses are 32-bit numbers, which can provide about 4 billion possible numbers. The newest version of the IP protocol (IPv6) offers an almost limitless number of unique addresses. For example, an IPv4 address looks like; an IPv6 address looks like 2001:4860:4860::8844.

Why IP Address Lookup Exists

An IP address is a lengthy string of numbers that is difficult for any computer user to remember, and it is susceptible to typographical errors. Instead, computer users enter URLs to go to websites. The URLs are easier to remember and type correctly. Behind the scenes, however, URLs must be translated to their corresponding lengthy numerical IP addresses to load the requested websites.

Typically, a user types a URL (commonly called a website address) into a web browser on a computer or mobile device. The URL goes to the router or modem, which performs a forward domain name server (DNS) lookup using a routing table. The resulting IP address identifies the website the user wants to view. The process is invisible to the user, who sees only the website corresponding to the URL typed in the address bar.

Most users rarely need to be concerned with reverse IP lookups. They are used mostly for network troubleshooting, often to find out the domain name of an IP address that is causing a problem.

Lookup Services

Several internet services support both forward and reverse IP lookup for public addresses. On the internet, these services rely on the Domain Name System and are known as DNS lookup and reverse DNS lookup services.

MX Toolbox DNS lookup

In a school or corporate local area network, private IP address lookups are also possible. These networks use internal name servers that perform functions comparable to those of DNS servers on the internet. In addition to DNS, the Windows Internet Naming Service is another technology that can be used to build IP lookup services on private networks.

Other Naming Methods

Years ago, before the advent of dynamic IP addressing, many small-business networks lacked name servers; they managed private IP lookups through host files. Host files contained simple lists of static IP addresses and associated computer names. This IP lookup mechanism is still used on some Unix computer networks. It can also be used on home networks that lack routers and with static IP addressing in place.

Dynamic Host Configuration Protocol (DHCP) automatically manages IP addresses within a network. DHCP-based networks rely on the DHCP server to maintain host files. In many homes and small businesses, the router is the DHCP server. A DHCP server recognizes a range of IP addresses, not a single IP address. As a result, the IP address may differ the next time a user enters a URL. Using a range of IP addresses allows more people to view the website simultaneously.

Utility programs provided with a computer's network operating system allow IP address lookups on both private LANs and the internet. In Windows, for example, the nslookup command (entered in a Command Prompt window) supports lookups via name servers and host files.

Screenshot of the 'nslookup lifewire.com' command in the Windows 10 Command Prompt
'nslookup lifewire.com' in Command Prompt.

The command is the same for macOS and is entered in a Terminal window.

nslookup in macOS

Public nslookup sites on the internet include Kloth.net, Network-Tools.com, and CentralOps.net.

Kloth.net DNS lookup