Nslookup

External

• https://linux.die.net/man/1/nslookup

Internal

• Linux

Overview

If nslookup is able to resolve the name, exits with 0, otherwise exits with 1.

Installation

With yum

yum install bind-utils

With apt

apt-get update
apt-get install dnsutils

Non-Interactive Mode

Getting the IP address for a name:

nslookup www.cnn.com
Server:		8.8.8.8
Address:	8.8.8.8#53

Non-authoritative answer:
www.cnn.com	canonical name = turner.map.fastly.net.
Name:	turner.map.fastly.net
Address: 151.101.0.73
Name:	turner.map.fastly.net
Address: 151.101.192.73
Name:	turner.map.fastly.net
Address: 151.101.64.73
Name:	turner.map.fastly.net
Address: 151.101.128.73

Debug Mode

To display protocol exchanges:

nslookup -debug google.com

Query Option

Getting more information for a name -query followed by a qualifier can be used. The qualifiers can be any DNS zone file element names (mx, a, txt, etc).:

• a a computer's IP address.
• any
• cname
• ns authoritative name server.
• hinfo a computer's CPU and type of operating system.
• mx mail exchanger.
• soa Start of Authority, technical information about the domain.

nslookup -query=hinfo www.cnn.com
Server:		8.8.8.8
Address:	8.8.8.8#53

Non-authoritative answer:
www.cnn.com	canonical name = turner.map.fastly.net.

Authoritative answers can be found from:
fastly.net
	origin = ns1.fastly.net
	mail addr = hostmaster.fastly.com
	serial = 2016110301
	refresh = 3600
	retry = 600
	expire = 604800
	minimum = 30

Getting the Mail Exchanger (MX) for a domain:

nslookup -query=mx novaordis.com
Server:		8.8.8.8
Address:	8.8.8.8#53

Non-authoritative answer:
novaordis.com	mail exchanger = 5 alt1.aspmx.l.google.com.
novaordis.com	mail exchanger = 5 alt2.aspmx.l.google.com.
novaordis.com	mail exchanger = 0 aspmx.l.google.com.
novaordis.com	mail exchanger = 10 aspmx2.googlemail.com.
novaordis.com	mail exchanger = 10 aspmx3.googlemail.com.

Obtain the Authoritative Answer

I was not able to find a way to configure nslookup to not return non-authoritative answers. The most reliable method to drop the non-authoritative answers seems to grep for NXDOMAIN.

However, if nslookup cannot resolve the name, it returns 1, otherwise returns 0.