I connect to a Synology NAS using NFSv4. Everything looks nice and read access works as expected. But writing produces the wrong uid gid on the server, i.e. writing a file produces a nobody:nogroup file on read or is denied, if the directory is not writeable by other.
Checking on the NAS I found out that the files created have the uid:gid of the client! I thought that the numerical ID weren't even transmitted in NFS4. But it could be coincidence of course.
I run idmapd with verbose 9. I see the read mapping, i.e. NAS name to client name, in the logs. These look fine, and as said they work fine. But I do not see what it does on write.
Any ideas how to troubleshoot?