I have a Mikrotik router that has 3 Internet connections.
1) PPPoE connection - Public IP address gets assigned to the PPPoE interface of the router
2)Fiber connection where ISPs PON does not allow a public IP address to be assigned. (Behind a double NAT)
3)USB LTE (Behind a double NAT)
Only the connection 1 lets me access the network/router from the Internet and I would like to force Router OS DDNS (Mikrotik Cloud) to use the PPPoE interface to fetch the IP address, even if network 1 is down and networks 2 and 3 are up.
Also, I'd like to add here that connection 2 is my primary Internet connection, 1 is the secondary and 3 is the tertiary connection (Distance of 1, 2 and 3)


Is there any way to force it use the PPPoE connection only for the DDNS update?

DDNS uses a host(s) at: cloud2.mikrotik.com
So the short answer is should be able to a use a firewall mange rule (combined with an a firewall address list for "cloud2.mikrotik.com") with a set routing action to the desired WAN.

"to use a specific interface"???
This mean that those interface have own gateway?
add a route to use that interface when 159.148.147.0/24 is the destination and to be reachable only by that gateway with distance=1.

Thanks, guys!
I was able to make it work.

Later realized this was already answered in viewtopic.php?p=962282&hilit=force+cloud+to+use#p962282