Nslookup: Difference between revisions
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=Overview= | =Overview= | ||
If nslookup is able to resolve the name, exits with 0, otherwise exits with 1. | |||
{{Warn|nslookup was found not work correctly on some busybox versions.}} | |||
=Installation= | =Installation= | ||
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==Debug Mode== | ==Debug Mode== | ||
To display protocol exchanges: | |||
<syntaxhighlight lang='bash'> | <syntaxhighlight lang='bash'> | ||
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* <code>any</code> | * <code>any</code> | ||
* <code>cname</code> | * <code>cname</code> | ||
* <code>ns</code> authoritative name server. | |||
* <code>hinfo</code> a computer's CPU and type of operating system. | * <code>hinfo</code> a computer's CPU and type of operating system. | ||
* <code>mx</code> mail exchanger. | * <code>mx</code> mail exchanger. | ||
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novaordis.com mail exchanger = 10 aspmx3.googlemail.com. | novaordis.com mail exchanger = 10 aspmx3.googlemail.com. | ||
</syntaxhighlight> | </syntaxhighlight> | ||
=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. | |||
Latest revision as of 05:04, 19 March 2020
External
Internal
Overview
If nslookup is able to resolve the name, exits with 0, otherwise exits with 1.
nslookup was found not work correctly on some busybox versions.
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).:
aa computer's IP address.anycnamensauthoritative name server.hinfoa computer's CPU and type of operating system.mxmail exchanger.soaStart 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.