hi
i have some mikrotik rb 433ah.
main mission internet access, 1 internet ip and NAT for some private networks.
but i have problem, if users from private network connect to 1 pptp server (in internet), only one can connect.
On another linux’like NAT systems, this problem can resolve by using:
ip_conntrack_proto_gre
ip_conntrack_pptp
ip_nat_proto_gre
ip_nat_pptp
how i can do this on microtik base rb ?
check out this slideshow by greg sowell
http://gregsowell.com/wp-content/uploads/2009/12/GregSowell-mikrotik-vpn1.pdf
you will need to take a like at pages 4 to 8
/ip firewall service-port
by the way, http://wiki.mikrotik.com/wiki/Manual:IP/Firewall/NAT#Properties , ‘connection-type’ property description contains a link named “/ip firewall service-port” and pointing to “/ip services” - MT Staff, please fix it 
tnx !ppl !