Learning All About Router

wo gateways failover with load balancing

First of all, you need a working system based on these examples: Improved Load Balancing over Multiple Gateways with Persistent Sessions or Improved Load Balancing over Multiple Gateways.
[edit] Route

According to the examples above, you have:

/ ip route
add dst-address=0.0.0.0/0 gateway=10.111.0.1 scope=255 target-scope=10 routing-mark=odd
add dst-address=0.0.0.0/0 gateway=10.112.0.1 scope=255 target-scope=10 routing-mark=even
add dst-address=0.0.0.0/0 gateway=10.112.0.1 scope=255 target-scope=10

Now you have to change these lines to:

/ ip route
add dst-address=0.0.0.0/0 gateway=10.111.0.1 scope=255 target-scope=10 routing-mark=odd check-gateway=ping
add dst-address=0.0.0.0/0 gateway=10.112.0.1 scope=255 target-scope=10 routing-mark=even check-gateway=ping
add dst-address=0.0.0.0/0 gateway=10.112.0.1 scope=255 target-scope=10
add dst-address=0.0.0.0/0 gateway=10.111.0.1 scope=255 target-scope=10 distance=2

If ping fails to 10.111.0.1, then all traffic marked odd go's to the gateway 10.112.0.1, the oposite is also true.

All local traffic go's to the 10.112.0.1 as it's distance is smaller, if 10.112.0.1 fails, then 10.111.0.1 takes over.

The router pings gateway every 10 seconds and if to consecutive pings to the gateway fail, the route is considered dead. So, then testing keep in mind, that gateway failure is detected in 20 to 30 seconds.
[edit] NAT

/ ip firewall nat
add chain=srcnat connection-mark=odd action=src-nat to-addresses=10.111.0.2 \
to-ports=0-65535 comment="" disabled=no
add chain=srcnat connection-mark=even action=src-nat to-addresses=10.112.0.2 \
to-ports=0-65535 comment="" disabled=no

change to:

/ip firewall nat
add chain=srcnat src-address=192.168.0.0/24 action=masquerade