in this topic you can see that it works(but the soft version in 7.5)
http://forum.mikrotik.com/t/how-to-disable-ecmp-on-bgp/160663/1
in this topic you can see that it works(but the soft version in 7.5)
http://forum.mikrotik.com/t/how-to-disable-ecmp-on-bgp/160663/1