/ip firewall nat
add chain=dstnat in-interface=your-wan protocol=tcp src-address=145.x.x.x src-port=1234 dst-port=3099 action=dst-nat to-addresses=192.168.88.xx to-ports=3099
/ip firewall mangle
add chain=postrouting out-interface=xxx action=change-ttl new-ttl=set:56
add chain=forward connection-state=established,related dst-address=192.168.1.251
add chain=forward src-address=192.168.1.251
add action=fasttrack-connection chain=forward connection-state=established,related
add chain=forward connection-state=established,related