This tutorial explains Linux “nslookup” command, options and its usage with examples.
DESCRIPTION
nslookup is a network administration tool for querying the Domain Name System (DNS) to obtain domain name or IP address mapping or any other specific DNS record.
It is also used to troubleshoot DNS related problems. This article provides few examples on using the nslookup command.
nslookup can operate on both “Interactive mode” and “Non-Interactive mode”. Interactive mode allows the user to query the DNS-Server about various host, and domains. Non-Interactive mode allows the user to query the information for a host or domain.
In this article, all the commands explained are “Non-Interactive mode”.
Authoritative Answer vs Non-Authoritative Answer
Any answer that originates from the DNS Server which has the complete zone file information available for the domain is said to be authoritative answer.
In many cases, DNS servers will not have the complete zone file information available for a given domain. Instead, it maintains a cache file which has the results of all queries performed in the past for which it has gotten authoritative response. When a DNS query is given, it searches the cache file, and return the information available as “Non-Authoritative Answer”.
SYNOPSIS
nslookup [ – option ] … host [ server ]
OPTIONS
all
List the current settings
d2
Set exhaustive debug mode on
nod2
Set exhaustive debug mode off
debug
Set debug mode on
nodebug
Set debug mode off
defname
Set domain-appending mode on
nodefname
Set domain-appending mode off
domain=string
Establish the appendable domain
ignoretc
Set it to ignore packet truncation errors
noignoretc
Set it to acknowledge packet truncation errors
host
Inquires about the specified host. In this non-interactive command format, nslookup Does not prompt for additional commands.
–
Causes nslookup to prompt for more information, such as host names, before sending one or more queries.
server
Directs inquiries to the name server specified here in the command line rather than the one read from the /etc/resolv.conf file. server can be either a name or an Internet address. If the specified host cannot be reached, nslookup resorts to using the name server specified in /etc/resolv.conf.
EXAMPLES
1. Simple Example
Looking up google.com
$ nslookup google.com
Server: 127.0.1.1
Address: 127.0.1.1#53
Non-authoritative answer:
Name: google.com
Address: 74.125.200.138
Name: google.com
Address: 74.125.200.113
Name: google.com
Address: 74.125.200.102
Name: google.com
Address: 74.125.200.100
Name: google.com
Address: 74.125.200.101
Name: google.com
Address: 74.125.200.1392. Query the MX Record using -query=mx
MX ( Mail Exchange ) record maps a domain name to a list of mail exchange servers for that domain.
$ nslookup -query=mx google.com Server: 127.0.1.1 Address: 127.0.1.1#53 Non-authoritative answer: google.com mail exchanger = 10 aspmx.l.google.com. google.com mail exchanger = 50 alt4.aspmx.l.google.com. google.com mail exchanger = 40 alt3.aspmx.l.google.com. google.com mail exchanger = 30 alt2.aspmx.l.google.com. google.com mail exchanger = 20 alt1.aspmx.l.google.com. Authoritative answers can be found from: google.com nameserver = ns4.google.com. google.com nameserver = ns3.google.com. google.com nameserver = ns1.google.com. google.com nameserver = ns2.google.com. alt2.aspmx.l.google.com internet address = 74.125.137.27 alt1.aspmx.l.google.com internet address = 74.125.142.26 aspmx.l.google.com internet address = 74.125.129.27 alt4.aspmx.l.google.com internet address = 173.194.75.27 alt3.aspmx.l.google.com internet address = 173.194.68.26 ns2.google.com internet address = 216.239.34.10 ns3.google.com internet address = 216.239.36.10 ns4.google.com internet address = 216.239.38.10 ns1.google.com internet address = 216.239.32.10
3. View available DNS records using -query=any
Using -query=any, we can get all records
$ nslookup -query=any google.com Server: 127.0.1.1 Address: 127.0.1.1#53 Non-authoritative answer: google.com origin = ns1.google.com mail addr = dns-admin.google.com serial = 2013121300 refresh = 7200 retry = 1800 expire = 1209600 minimum = 300 google.com mail exchanger = 10 aspmx.l.google.com. google.com mail exchanger = 40 alt3.aspmx.l.google.com. google.com mail exchanger = 30 alt2.aspmx.l.google.com. google.com mail exchanger = 50 alt4.aspmx.l.google.com. google.com mail exchanger = 20 alt1.aspmx.l.google.com. google.com has AAAA address 2404:6800:4003:c00::65 Name: google.com Address: 74.125.200.139 Name: google.com Address: 74.125.200.102 Name: google.com Address: 74.125.200.138 Name: google.com Address: 74.125.200.113 Name: google.com Address: 74.125.200.100 Name: google.com Address: 74.125.200.101 google.com nameserver = ns4.google.com. google.com nameserver = ns2.google.com. google.com nameserver = ns3.google.com. google.com nameserver = ns1.google.com. Authoritative answers can be found from: google.com nameserver = ns3.google.com. google.com nameserver = ns4.google.com. google.com nameserver = ns2.google.com. google.com nameserver = ns1.google.com. alt3.aspmx.l.google.com internet address = 173.194.68.27 alt2.aspmx.l.google.com internet address = 74.125.137.26 alt4.aspmx.l.google.com internet address = 173.194.75.27 alt1.aspmx.l.google.com internet address = 74.125.142.26
4. Reverse DNS lookup
Looking up IP address to get the domainname.
$ nslookup 173.194.68.27 Server: 127.0.1.1 Address: 127.0.1.1#53 Non-authoritative answer: 27.68.194.173.in-addr.arpa name = qa-in-f27.1e100.net. Authoritative answers can be found from: 194.173.in-addr.arpa nameserver = NS2.GOOGLE.COM. 194.173.in-addr.arpa nameserver = NS4.GOOGLE.COM. 194.173.in-addr.arpa nameserver = NS3.GOOGLE.COM. 194.173.in-addr.arpa nameserver = NS1.GOOGLE.COM. NS3.GOOGLE.COM internet address = 216.239.36.10 NS4.GOOGLE.COM internet address = 216.239.38.10 NS2.GOOGLE.COM internet address = 216.239.34.10 NS1.GOOGLE.COM internet address = 216.239.32.10
5. Using Specific DNS server
In the following wxample ns1.google.com is the specific name server which is being looked up.
$ nslookup google.com ns1.google.com
Server: ns1.google.com
Address: 216.239.32.10#53
Name: google.com
Address: 173.194.36.0
Name: google.com
Address: 173.194.36.5
Name: google.com
Address: 173.194.36.7
Name: google.com
Address: 173.194.36.9
Name: google.com
Address: 173.194.36.2
Name: google.com
Address: 173.194.36.1
Name: google.com
Address: 173.194.36.8
Name: google.com
Address: 173.194.36.14
Name: google.com
Address: 173.194.36.3
Name: google.com
Address: 173.194.36.4
Name: google.com
Address: 173.194.36.6Here you may notice that, we don’t get any “Non-authoritative answer:” header, since ns1.redhat.com has all the zone information of redhat.com
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