I have a network like this , I would like to have 192.168.51.241 as main internet gateway and if the link gets down the client with 192.168.10.47 IP can access to internet from 172.19.21.153.
Notice : when I want to access to internet from my main link I should make a scr-nat , and action src-nat to a valid IP but I can masquerade users to use 172.19.21.153 gateway….

http://wiki.mikrotik.com/wiki/Advanced_ ... _Scripting

I try to do it but it cant switch between nat ruls....