Hi, i have RB750G with RouterOS 4.17.
I have two ppp client connections active. One of them is default, so all my internet traffic is going by them.
How can i do a proxy, where all traffic will be going only by second pptp ? For example, when i typing in some app proxy 192.168.88.1:3128, traffic will be going by that second pptp interface. It's in NAT of Filters, but i dont find how can i forward to another interface.
Thank you. Native language is not english, so, maybe will be some troubles to take a sense of writing by me

http://wiki.mikrotik.com/wiki/Manual:IP/Proxy

src-address (Ip4 | Ip6; Default: 0.0.0.0) Proxy will use specified address when connecting to parent proxy or web site. If set to 0.0.0.0 then appropriate IP address will be taken from routing table.

First make a loopback interface by creating a new bridge interface, not adding any ports to it, and giving it an IP address. You can now reach the router via that IP.
Then set that IP as the src-address of the proxy, and do not ever use it for anything else.
Then make mangle rules in the "output" chain that set a routing mark for traffic sourced from that loopback IP address, and finally make a route for 0.0.0.0/0 and that routing mark to go out the second PPTP interface, and ensure the distance of that route is lower than your other default routes.

The idea is to get the proxy to use IP patterns that you can recognize in firewall rules, and to then use policy routing to force only proxy traffic out a particular WAN interface.

All is clear, but not with routing mark.
Can you explain it more detailed how can i do this right, please ?

Substitute as required. Make sure the distance for existing routes is higher than the new one added above.

Thank you!