If I set up backup nas as target and bring it in office it works (the Synology just uses rsync and listens on 873) If I bring backup nas home and forward port 873 to outside and tell master nas to ...

This is a software question, but it's about Synology hardware which is usually talked about here. I have two Synology's and I'm trying to back Synology 1 up to Synology 2. Synology 1 and 2 are on the ...