Microtik behind Microtik (with NAT)

RouterOS General
1

At a specific client site the ISP uses a Microtik router for the connection, the NAT, DHCP, DNS as well as some bandwith control rules.
The client wants further restrictions implemented, and are very happy with Microtik solutions that I installed at their other branches (where MY microtik handles all the tasks)
BUT at this site the ISP insists that it will not change the config on their router, according to their contract fine print, their router has to be in place as is, with no modification made to it.

So I need to add my routerBOARD between the LAN and the ISP-Router, and let the ISP router continue to handle NAT, DHCP and DNS, so that both the rules on their router and the rules on my router are applied to the traffic.

I am not quite sure how to allow the pass through without NAT on my router.
Some links to related material will be handy.
(not looking to be spoon fed, just a kick in the right direction will help)
Many thanks.

2

See if the ISP is willing to install a route to your internal network IP range by the IP addressed assigned to your MikroTik. That is really the best way to do it without NAT.

If they are not, you can try using a bridge with your MikroTiks WAN and LAN ports, and have “Use IP Firewall” checked on the bridge configuration. This gets a bit more tricky, but should be doable, and allow you to use most of your built in firewall rules with little modification.

3

Yes, if they route all traffic to my routerBoard IP … this will require some testing. I will update if I make any progress.
Thanks for the ideas.