I have asked similar question
http://forum.mikrotik.com/t/l2tp-to-specific-port-on-switch/142367/1
Apparently it’s IPv4 - Firewall - Mangle: rule that will do the job 
Searching now how to achieve this
I have asked similar question
http://forum.mikrotik.com/t/l2tp-to-specific-port-on-switch/142367/1
Apparently it’s IPv4 - Firewall - Mangle: rule that will do the job
Searching now how to achieve this