How Cani Do this? Please Help me with command details.
L2TP to the RB450 ? 
Hi..
At this case there is several thing need to take in consider..
If the customer have its own IP range.. mean its should be routed some how… from internet to your network..
BGP connection need to be established between you and you customer ..
Also you should have BGP connection with at least one ISP..
And then you need to advertise you customer ip address to the internet..
Please let me know if all are clear..
If you would like to have some more help in configuration just need more info about
-Your ASN number
-your IP range
-Customer ASN number
-Customer IP range
Also you need to have some access to IR like RIPE.. to create new route object
Best regards
Ali Sami
MikroTik trainer
You can src-nat user’s private address (ports 0-65535) to one public address (ports 0-65535) and dst-nat the same address back to his private address.
Customer will be accessible by the public address and all his outgoing traffic will be “signed” by the same address.
I have just tried it on my test router and it works perfectly
add action=dst-nat chain=dstnat disabled=no dst-address="public IP" dst-port=0-65535 port="" protocol=tcp src-port="" to-addresses="private IP" to-ports=0-65535
add action=src-nat chain=srcnat disabled=no dst-port=0-65535 protocol=tcp src-address="private IP" to-addresses="public IP" to-ports=0-65535
Does this solve your problem?
Regards