How possible it is to run an advertising script that will be pulling out advertising banna at the top of every web browsers of the client that will be connected through the mikrotik gateway?
It is possible with the HotSpot, for regular clients it is hard to do.
http://www.mikrotik.com/testdocs/ros/3.0/pnp/hotspot.php
Can you access http://www.anchorfree.com and see the kind of advertising technology am talking about.
They have an open VPN connection and any client that connect through it most view the advert on each browser.
injecting custom code into every webpage would be very resource intensive, and could break a lot of sites. it’s risky and not easy to make.