I am considering buying the Synology DiskStation DS115j after discussion at my previous question (how can NAS work if it is not connected to Internet?). Before I did that, I wanted to read through instructions about how to set it up with Mac's Time Machine, to make sure it would be easy. I found the instructions here: https://www.synology.com/en-us/knowledgebase/DSM/tutorial/Backup_Restore/How_to_back_up_files_from_Mac_to_Synology_NAS_with_Time_Machine
The instructions are pretty straightforward but there is one unsettling part: search for "Enter the address of your NAS server." Basically it seems that to connect one's Mac to the Synology NAS, you have to provide an IP address.
First of all, they don't explain how to determine the IP address of your Synology NAS. How do you do that? Second of all, a bigger concern is that if I'm not mistaken, that IP address can change whenever the NAS reconnects to the router (for example, if you restart your router). Doesn't that mean that your Mac's connection to the Synology NAS would break whenever either the router or the NAS is restarted, since it is based on this IP address?