I set up NAT on my Mikrotik (M-OSPF-15). Router goes online (pings ya.ru, vk.com, etc.).
Need to configure access to the Internet for all routers from the zone OSPF, as other routers do not have this option (not pinging ya.ru, vk.com, etc.).
Option with forwarding default route to the router, which sends traffic (M-OSPF-15), falls out, because the default route can only be one, and there may be several routes to M-OSPF-15.
I work in an EVE-NG virtual lab.
P.S.: I just understand networks, if any details are missing - write. Explained as best I could.