How do I get `apt-get update` to work on a machine with no internet access and manually assigned IP address?

I found the solution to be to edit the etc/apt/sources.list file to include files of only the system's architecture:

deb [arch=amd64] http://192.168.12.61/ubuntu/ xenial main restricted multiverse universe

Now when I do the update, its not giving any error:

$ sudo apt update
Hit:1 http://192.168.12.61/ubuntu xenial InRelease
Reading package lists... Done
Building dependency tree       
Reading state information... Done
All packages are up to date.

Just thought of posting this as a possible solution for anyone who might be having the same issue.