Понятно, как настроен dual-wan? А вообще статья в закрепе, там есть примеры и с vpn.
/ip firewall mangle
add action=accept chain=prerouting disabled=yes dst-address=2.2.2.0/18 \
in-interface=ether2-DOMRU
add action=accept chain=prerouting disabled=yes dst-address=1.1.1.0/29 \
in-interface=ether1-RT
add action=mark-connection chain=prerouting connection-mark=no-mark disabled=\
yes in-interface=ether2-DOMRU new-connection-mark=connection_bks \
passthrough=yes
add action=mark-connection chain=prerouting connection-mark=no-mark disabled=\
yes in-interface=ether1-RT new-connection-mark=connection_RT passthrough=\
yes
add action=mark-connection chain=prerouting comment="2/0 RT" connection-mark=\
no-mark disabled=yes dst-address-type=!local in-interface=bridge \
new-connection-mark=connection_RT passthrough=yes \
per-connection-classifier=src-address-and-port:2/0
add action=mark-connection chain=prerouting comment="2/1 domru" \
connection-mark=no-mark disabled=yes dst-address-type=!local \
in-interface=bridge new-connection-mark=connection_bks passthrough=yes \
per-connection-classifier=src-address-and-port:2/1
add action=mark-routing chain=output connection-mark=connection_bks disabled=\
yes new-routing-mark=route_bks passthrough=yes
add action=mark-routing chain=output connection-mark=connection_RT disabled=\
yes new-routing-mark=route_rt passthrough=yes