Turns out there was a “security” feature enabled on our PowerConnect switch that took offense to NFS SYN packets with source ports < 1024 (dos-control tcpflag). Suffice it to say, disabling the feature solved the issue.
Reading this again I think this is actually the case here. Why? Because I made Miguel try telnet <fog-server-ip> 56557 (the actual NFS data port) and it worked - as telnet is not using a high source port I suppose.
I think fog 1.2 is not totally compatible with synology nas because synology use two different path to access data over NFS & FTP (/volume1/images & /images)
and on fog storage node interface you can only set one path.
(Fog does the rename job with the ftp account.)
you need to go with a newer fog version to have the “ftp path” option.