HowTo: Find Out DNS Server IP Address Used By My Router?

My router configured by ISP tech and it is set to get DNS server address automatically from upstream. Is there is a way to find out the IP address of the dns server used by my router which is located at 192.168.1.1? Is there Linux, Unix, Apple OS X, or MS-Windows command that I can use get the same information?

Domain Name System (DNS) is an Internet service that translates domain names into IP addresses or vice versa. The easiest way to find out your dns server IP address is to go through the router’s admin interface status page. All routers have a built-in web-based setup page that allows the user to customize settings and set view properties such as IP address and dns settings.

Method #1: Router’s Webgui Status Page (Recommended for all users)

You can use router’s web gui page to find out dns server IP address assigned by your ISP.

  • First, open a web browser (use your computer’s web browser such as Firefox, Google Chrome, or Internet Explorer).
  • Type the router’s IP address on the Address bar on top then press Return ([Enter] key] on your keyboard. In most cases the router’s default IP address is 192.168.1.1 (see how to find out router’s IP address under MS-Windows and Unix like operating system).
  • Enter your router’s username and password when prompted.
  • You should see router page like the one below (the page varies depending on the router make and model).
Fig.01: My linksys home router
  • Finally, click on Status to view dns address assigned by your ISP. You should see status page like one below (again page output varies on the router make and model but you should able to see dns server IP address)
Fig.02: My linksys router's dns server settings assinged by my isp

Method # 2: MS-Windows Commands

Open a command prompt (click on Start > run > type cmd and press [enter] key to open a command prompt).

Type the nslookup command to check DNS resolution at the command prompt c:>
nslookup sxi.io
OR
nslookup www.google.com
Sample outputs:

nslookup sxi.io
Server:		dns2.mumbai.corp-lan.nixcraft.net.in
Address:	10.0.80.11#53

Non-authoritative answer:
Name:	sxi.io
Address: 75.126.153.206

The first two lines are the dns server (10.0.10.11 or dns2.mumbai.corp-lan.nixcraft.net.in) you are using i.e. dns server IP address assigned by your ISP or network admin. 10.0.80.11 is our own dns server located inside our corporate network.

Say hello to ipconfig /all command

Another option is to type ipconfig /all command at the command prompt to get the same information:
ipconfig /all
Sample outputs:

Fig.03: MS-Windows command to find out DNS server IP addresses

In this example my DNS server is located at 192.168.1.2. This one is used by my computer, and it was passed on to my computer by ISP modem / router.

Method #3: Apple OS X or Unix / Linux Commands

Open the bash shell prompt and type the dig or host commands:
$ host -a sxi.io | grep from
Sample outputs:

Received 229 bytes from 10.0.10.11#53 in 0 ms

OR use the dig command:
$ dig sxi.io | grep SERVER
Sample outputs:

;; SERVER: 10.0.10.11#53(10.0.10.11)

However, a better approach is to go through /etc/resolv.conf file to see assigned dns server address to your computer. It was passed on to you by your modem / router:
$ cat /etc/resolv.conf
Sample outputs:

nameserver 10.0.80.11
nameserver 10.0.80.12
options single-request

Method #4: Dump and view traffic on a network (recommended for advanced users only)

You can use the tcpdump command to dump traffic on a network and view dns traffic. tcpdump command works on most Unix-like operating systems. tcpdump command analyzes network behavior, performance and applications that generate or receive network traffic including dns traffic. To view dns traffic only run tcpudmp as root user in a separate window:
# tcpdump udp and src port 53
# tcpdump udp and dst port 53
# tcpdump -n -s 1500 -i eth0 udp port 53

Open another window (terminal) and run host / dig commands to generate dns traffic:
$ host sxi.io
Sample outputs:

Fig.05: Tcpdump in action – monitoring udp port # 53 traffic

In this example:

  1. You see all packets going in and out of my Linux system for udp port # 53.
  2. I ran host command from another windows.
  3. The output of tcpdump clearly indicate that my computer (IP:192.168.1.5) asking to dns server (IP:192.168.1.2) about the address of sxi.io? In second line I got answer from dns server.

Posted by: SXI ADMIN

The author is the creator of SXI LLC and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.