In my office network i unknowingly changed a setting of my gateway of lan network .. I had set my phone's ip address under a section in setting which states that.. Only this ip can login to the network.. And the ip which i filled in was of my phone which is connected to my office wifi network.. Due to this reason none of the computer in the lan network can access the router's login page.. I had used the gui interface.. So now i need to know my lan's router external ip address.. So thar i can access the router login page on my phone
you can just visit https://www.whatismyip.com/ and the site will tell you what your external IP address is.
Connect an Ethernet cable directly to your router, If the router is set to use DHCP, wait to get an IP on your computer, then open CMD and type ipconfig You will see the IP, Subnet and Default Gateway IP
If you router is not using DHCP, assign the same IP range to your NIC (Same IP as your Phone Ex. If your phone is using 192.168.1.27, assign 192.168.1.200 to your NIC manually) and connect directly to your router using an Ethernet cable, then open CMD and type ipconfig You will see the IP, Subnet and Default Gateway IP. Make sure is using the same as your phone.
You will able to login to the router and make the necessary changes to fix the issue.