computer science

Nslookup

Nslookup is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Nslookup rather than just read about it. In short: nslookup (from name server lookup) is a network administration command-line tool for querying the Domain Name System (DNS) to obtain the mapping between domain name and IP address, or other DNS records. Overview nslookup is a member of the BIND name server software.

Key takeaways

Nslookup belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Nslookup to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nslookup from memory before moving on to harder problems.

Reference excerpt

nslookup (from name server lookup) is a network administration command-line tool for querying the Domain Name System (DNS) to obtain the mapping between domain name and IP address, or other DNS records.

Overview nslookup is a member of the BIND name server software. Andrew Cherenson created nslookup as a class project at UC Berkeley in 1986 and it first shipped in 4.3-Tahoe BSD. In the development of BIND 9, the Internet Systems Consortium planned to deprecate nslookup in favor of host and dig. This decision was reversed in 2004 with the release of BIND 9.3 and nslookup has been fully supported since then. Unlike dig, nslookup does not use the operating system's local Domain Name System resolver library to perform its queries, and thus may behave differently. Additionally, vendor-provided versions may include the output of other sources of name information, such as host files, and Network Information Service. Some behaviors of nslookup may be modified by the contents of resolv.conf. The Linux version of nslookup is the original BSD version written by Andrew Cherenson. The ReactOS version was developed by Lucas Suggs and is licensed under the GPL.

Usage nslookup operates in interactive or non-interactive mode. When used interactively by invoking it without arguments or when the first argument is - (minus sign) and the second argument is a hostname or Internet address of a name server, the user issues parameter configurations or requests when presented with the nslookup prompt (>). When no arguments are given, then the command queries the default server. The - (minus sign) invokes subcommands which are specified on the command line and should precede nslookup commands. In non-interactive mode, i.e. when the first argument is a name or Internet address of the host being searched, parameters and the query are specified as command line arguments in the invocation of the program. The non interactive mode searches the information for a specified host using the default name server.

See also dig, a utility that interrogates DNS servers directly for troubleshooting and system administration purposes. host is a simple utility for performing Domain Name System lookups. List of DNS record types - possible types of records stored and queried within DNS Root name server - top-level name servers providing top level domain name resolution whois BIND name server

References

Further reading Barrett, Daniel J. (2012). Macintosh Terminal Pocket Guide: Take Command of Your Mac. O'Reilly. ISBN 978-1449328986. Stanek, William R. (2008). Windows Command-Line Administrator's Pocket Consultant, 2nd Edition. Microsoft Press. ISBN 978-0735622623.

External links

Microsoft Windows

nslookup – Microsoft TechNet library Using NSlookup.exe, Microsoft Knowledge Base Unix-like OSs

nslookup(1) – Linux User Commands Manual nslookup source code in ISC Gitlab repository (Mozilla Public License) Web Tools

DNS Lookup

Illustrations

Worked examples

Example 1 — a first encounter with Nslookup

Start with the simplest possible case. Write down what Nslookup claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nslookup before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nslookup ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nslookup

In research: Nslookup appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nslookup in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nslookup is common in secondary-school and first-year university syllabi. It links to neighbouring topics DNS software, Internet Protocol based network software, OS/2 commands, so understanding it makes those chapters shorter.
In everyday life: Look for Nslookup outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Nslookup in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nslookup means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nslookup out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nslookup in simple terms?

Why does Nslookup matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nslookup?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nslookup.