/ip firewall mangle
add action=mark-routing chain=prerouting disabled=yes dst-address=1.1.1.1 \
new-routing-mark=for-l2tp port=1701 protocol=udp
/ip route
add comment="" disabled=no distance=1 dst-address=1.1.1.1/32 gateway=x.x.x.x \
routing-mark=for-l2tp scope=30 target-scope=10