Skip to main content

nslookup Command

A Network Administrator command  which help diagnosis DNS related issue. However to understand this,  you should better to know how DNS works.

How to troubleshoot DNS related issue.

1. NSLOOKUP example display "A Record" (IP Adress) of the domain




C:\Users\jpudasaini>nslookup jpudasaini.com.np 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
Name:    jpudasaini.com.np
Address:  216.239.32.21

A Non-Authoritative Answer is a response from Cache. A DNS server is
authoritative for zones actually holds it.

The above output shows "A Records" (IP Adress) of the domain
"jpudasaini.com.np". Which is actually query to the public Google DNS. If
you don't put DNS after the domain, it will used your default DNS, in my
case I have used public DNS.

2. MX Record using -query=mx

MX (Mail Exchange) record maps for the specific domain name to verify mail
exchaing servers on that domain.


C:\Users\jpudasaini>nslookup -query=mx gmail.com 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
gmail.com       MX preference = 40, mail exchanger =alt4.gmail-smtp-in.l.google
.com
gmail.com       MX preference = 20, mail exchanger =alt2.gmail-smtp-in.l.google
.com
gmail.com       MX preference = 10, mail exchanger =alt1.gmail-smtp-in.l.google
.com
gmail.com       MX preference = 30, mail exchanger =alt3.gmail-smtp-in.l.google
.com
gmail.com       MX preference = 5, mail exchanger =gmail-smtp-in.l.google.com

From the above example we can say that  4 MX records used for gmail
domain, the number associat with mx reference the preference of mail
server. Lower the number, higher the preference. So
gmail-smtp-in.l.google.com is the first server which received the mail at
first.

3. NS Record using -query=ns

NS (Name Server) records maps a domain to a list of DNS servers
authoritative for that domain. Here is example of name server which are
associated with jpudasaini.com.np doamain.

C:\Users\jpudasaini>nslookup -query=ns jpudasaini.com.np 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
jpudasaini.com.np       nameserver = ns4.afraid.org
jpudasaini.com.np       nameserver = ns2.afraid.org
jpudasaini.com.np       nameserver = ns1.afraid.org

4. SOA Record using -query=soa

 C:\Users\jpudasaini>nslookup -query=soa jpudasaini.com.np 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
jpudasaini.com.np
        primary name server = ns1.afraid.org
        responsible mail addr = dnsadmin.afraid.org
        serial  = 1511030001
        refresh = 86400 (1 day)
        retry   = 7200 (2 hours)
        expire  = 2419200 (28 days)
        default TTL = 3600 (1 hour)

SOA record (start of authority) which provides the authoritative
information, as well as e-mail address, serial no of the respective
domain.


5. Reserve DNS lookup

The reverse DNS look-up using IP Adress as argument to nslookup
C:\Users\jpudasaini>nslookup 216.239.32.21 8.8.8.8
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Name:    any-in-2015.1e100.net
Address:  216.239.32.21


6. Using Specific DNS Server

Make query using particular name server instead of using default DNS server.


C:\Users\jpudasaini>nslookup jpudasaini.com.np ns1.afraid.org
Server:  UnKnown
Address:  50.23.197.95

Name:    jpudasaini.com.np
Address:  216.239.32.21
Labels:

Comments

Post a Comment

Popular posts from this blog

IOS XR GNS3 QEMU

This time lets have tutorial on Cisco XR 9k series router image running on the GNS3. Please don't ask for the XR image. Your are smart enough to get it. My system configuration: Ubuntu 16.04 GNS3 1.4 RAM 8Gig i7 processor Used XR Image iosxrv-k9-demo-6.0.1.qcow2 This image is VIRL extracted image. You need to convert this image into QEMU image, follow this link I strongly recommend you to run it on the Linux system. Now you have converted image, then go to the GNS3>Edit>Preferences>QEMU>Qemu VMs>New then follow the onscreen procedure. Setting for QEMU XR Image. RAM:- 4Gig CPU:- 1 Adapters at lest 4.  -enable-kvm Here you can see I can run the XR on my system. Interface is up and system is already booted.  I have run 3 XR router  here is my system RAM CPU usages. RP/0/0/CPU0:XR3(config)#int gi0/0/0/0 RP/0/0/CPU0:XR3(config-if)#ip add 192.168.13.2 255.255.255.252 RP/0/0/CPU0:XR3(con...
Post a Comment
Read more

Cisco ASA in GNS3

Here is another tutorial running Cisco ASAv on GNS3 using Qemu. For Configure GNS3 In My case I have used ASAv952-204.qcow2 Go  to the GNS3>Edit>Preferences>QEMU>Qemu VMs>New Follow on screen procedure.  Don't forget to enable kvm and memory allocation.  Now you can see I can run ASAv 9.5.2 Blank Password.
Post a Comment
Read more

Mikrotik Hotspot Redirect After Login

This tutorial assumed you already create Hotspot in your router. If you don't know how to create a hotspot in Mikrotik router, click here and create the Hotspot. . After successfully creating the hotspot server go to "Files" Menu of  the main Window of Mikrotik router Copy "hotspot" folder into your PC. Open "alogin" file with text editor Replace "link-redirect" text with your desire URL Now you're done! After successfully logging into the Hotspot server your client automatically redirects to your external link.  Don't forget to copy this folder into Mikrotik Router "Files" Menu. You can also drag and drop this folder into "Files" menu. 
8 comments
Read more