Multiple IP's on Linux servers

Anurag Bhatia
One of things which people often asked me around in past was on how to have multiple IPs on Linux machine under various circumstances. I know there are ton of blog posts about this but very few explain how it works and possible options under different use cases etc. I will share router side and server side config with focus on how it should be done from server end. Assuming server side config to be for Ubuntu/Debian.