I bought a new RB4011 and am stuck on NAT

RouterOS Beginner Basics
1

Need guidance configuring RB4011 NAT to my home fiber router as WAN link

2

The simplest option is to use the RB4011’s default configuration and put the fiber ONT into bridge mode. Don’t reject this solution before reading the linked article to the level that you can explain — coherently! — why it does not do everything you need.

If for some reason you have to leave the ONT in its stock mode, then you’re stuck with these options, as I see it:

  1. Double NAT: the ONT may use PPPoE to get an IP address and do NAT of its own, which it then masquerades on the LAN side with DHCP, which your shiny new router then goes and does similar things under the default configuration.
  2. Turn the RB4011 into a smart switch (also touched on in that linked article) so that it is just one peer among all the others connected to it to get its IP via DHCP from the ONT.
  3. Get a static IP range from your ISP so that you can use the RB4011 as a proper router without NAT. IPv6 makes this straightforward. The IPv4 path is expensive if you want it to be simple, and complex if you want it to be cheap.
3

Chesterton's Fence :+1:
https://en.wikipedia.org/wiki/G._K._Chesterton#Chesterton's_fence

4

Without knowing where the OP is and their ISP, we do not know whether stock mode is router or bridge. Where I am, it can be either and for the largest network the ONT can only be in bridge mode.

@Time can you confirm whether your ONT is in bridge or router mode?

5

Why did you decide to buy an OLD router? Specifically arm32 which is being less and less supported by MT firmware functionality, to the point they actually provided an upgrade path for the L1009 to be arm64 architecture. If you can, I highly recommend returning the unit and getting something like the RB5009, which besides ARM64, can easily handle 1gig fiber speeds and future growth having (one up to 2.5gig port and one up to 10gig port).