Solution:

Yes. These units come with a default Port number starting with port 4000. So all the units will have the same port numbers. If you have multiple units that you wish to access from outside the local LAN, you will need to assign each ESP/ESR a unique port number, so that you can do port forwarding to each individual port. You can connect to multiple ESP/ESR units within the LAN without changing the default port number, but to access them over a WAN you have to give them unique port numbers.