I am connecting with internet via mikrotik.
Is it possible that all the traffic to internet (vice versa) pass throw a backup line (2nd line to internet) when the first path (line) is down? Please, how can I do?
You can achive this by adding the second gateway with higher metric meaning distance=5 e.g and also allow check-gateway=ping in both default routes. With this as soon as primary link goes down it will activate the back-up link, than as soon as primary link comes up you will be redirected through primary link.