varunendra, sorry for not writing to you earlier.
About two weeks ago I moved into a new apartment with a provided cable internet. What I did there was:
1) assigned MAC address as I did previously:
2) assigned arbitrary, but existing IP address. I took the address from another country!
sudo ifconfig eth0 hw ether 00:22:19:ff:2f:ee
The internet works.
sudo ifconfig eth0 xx.xx.xx.xx
So, as a concluding word, I'm not gonna use my laptop for ethernet connection anywhere except when at home. When I use it at home, each time after reboot I have to enter these two commands in the terminal. After three years of no ethernet at all, than't not a pretty bad deal, if you think about it.
Thank you for your help. I wouldn't have obtained the internet if you hadn't been doing all those experiments described above. Although I understand the behavior we were witnessing still seems confusing to you.
I wish you all the best. Bye!