I have two RBs with 3 WANs each. For example RB1 and RB2 :
RB1 Wan´s :
1A(eth1) / 1B(eth2) / 1C(eth3)
RB2 Wan´s :
2A(eth1) / 2B(eth2) / 2C(eth3)
In both RBs the same configuration of IP/ROUTES (1A and 2A are the default gateways), B and C are for ROUTING-MARK traffic (Working Well), and at the same time are configured as DEFAULT GATEWAY with a GREAT COST/DISTANCE.
The problem : If I want to access with winbox via WAN B or C, the RBs receive the INPUT PACKETS in the correct INTERFACE (Eth2 or Eth3), but I saw that it send the OUTPUT PACKETS with the WAN A Interface (Eth1)
I have an old version of OS (3.30), but I not sure that the problem is the version…
Look up policy based routing. Basically you need to define rules that watch for connections coming into the router on a specific interface and mark those connections and packets for routing so it knows what route to use when sending the reply back. Without those rules, it falls through to the main routing table and becomes an invalid connection to you.