I would be remiss in not stating......Very happy to have an active {MANGLE RULE} contributor, just wanted to say that as I was getting tired of being corrected by Sob and Sindy and CZFAN etc.............. Good to have fresh blood!!
Concur, there seems to be a mismatch in the LAN configuration.
Furthermore, the dstnat rule is very confusing...........
Lets assume Mangle has the setup right and one cannot dispute his assumptions based on the given information.
Thus the Mikrotik is double natted which is never a good idea IMHO but in any case a client on the mikrotik should be able to access a client on the modem router (but not the reverse).
For me the first thing I would do is change the ISPs unit to modem only (bridge mode) and have the mikrotik do all the routing. However that is not the question.
Concur with MangleR that the masquerade rule on the mikrotik (which is no different from what the OP had already written?) seems fine and is the only item required.
Can you spot any differences?
/ip firewall nat add chain=srcnat out-interface="ether-WAN" action=masquerade - MangleR
/ip firewall nat
add chain=srcnat action=masquerade out-interface=ether-WAN comment="Default masq" - Op
Where I see the issue is the DSTnat rule.
One still needs port forwarding in a double nat scenario where if someone from the internet wishes to access a server on the mikrotik LAN, one has to dstnat from the modem/router to the mikrotik wanip (lanip on ISP router/modem network) and then dstnat to the server on the mikrotik.
All well and good but useless for this question as we are simply looking for
client to client access. There is no requirement to port forward to the IP CAM on the mikrotik router because it is
NOT ON THE MIKROTIK LAN!! So the only port forwarding that needs to be done is on the ISP modem/router if the OP wishes internet (remote access to ipcam).
Thus I find the dstnat rule confusing, not useful and should be removed.
add chain=dstnat action=dst-nat in-interface=ether-WAN protocol=tcp dst-address=192.168.0.1 to-addresses=192.168.1.15 dst-port=8080 to-ports=8080
Even if the IPCAM was on the mikrotik LAN (192.168.0.15), the dstnatrule would probably look like
add chain=dstnat action=dst-nat in-interface=ether-WAN dst-port=8080 protocol=tcp to-addresses=192.168.0.15
Okay, that aside, the issue is most likely on the ISP modem/router side in terms of a funky setup?
Any query by a client on the mikrotik network should go out the mikrotik wan (and with the srcnat masquerade rule in-place and thus appear to be coming from 192.168.1.XX) and be allowed to, on layer 2, to access 192.168.1.15. (note: xx is the LANIP given to the mikrotik router by the DHCP of the ISP modem router (or the OP if statically assigned)
A browser query from any client behind the mikrotik should simply work -
http://192.168.1.15:8080
You never did post any routing or firewall filter rules which may be blocking????
Perhaps Mangle can fix you up with a way to log the traffic request to see where it stops.........