First, I'm going to assume you're using IPv4 with NAT, and not IPv6. (IPv6 makes it easy. In fact, if you had IPv6, it would probably already work for you by default. Actually, it's probably more fair to just say doing stuff without NAT makes it easy, but that's usually not an option on IPv4.)
Assuming your router is using IPv4 NAT, you will need to set up something commonly referred to as port forwarding. It allows you to map a port on your Mikrotik router to be passed on to a server's port.
In essence, you will be setting up a rule that tells the Mikrotik router that if it sees traffic address to it on port X, re-write that traffic on the fly to be addressed to your server's internal IP (usually starts with 10.
or 172.16.
or 192.168.
) address on port Y.
Here's how it's done on a Mikrotik router:
First, go to the IP menu on the left, and then Firewall. Then make sure you are on the NAT tab, and then click the "Add New" button.
You will be taken to a screen like this:
For chain, pick dstnat. Clik the arrow pointing down next to Dst. Address and then enter the address that you can access your Mikrotik router by from the internet. Unless you know you are using UDP ports, click the down arrow next to protocol and leave it at 6 (tcp)
. For the Dst. Port, again, click the down arrow, and enter the port you want to use on the internet to access your server.
Now scroll down the page:
For action, select dst-nat. Change the "To Address" to the internal IP address of your server (again, this should start with 10.
or 172.16.
or 192.168.
). Change the "To Port" to the port of the service on your server.
Finally, click OK
(if you want to leave the page and put the settings in place) or Apply
(if you want to put the settings in place and stay on the page to tweak them).
Oh, and if you prefer the command line way, you can do something along the lines of this:
/ip firewall nat add chain=dstnat dst-address=69.69.69.69 protocol=tcp dst-port=5900 \
action=dst-nat to-addresses=192.168.1.101 to-ports=5900
Based of the Mikrotik wiki page on port forwarding.