When upgrading in-place to 10.13 (High Sierra) from 10.12.6 (Sierra build 16G29), my customized nsmb.conf file was intact.





As a side note, I appears that my cutomized sysctl.conf file is also intact, too (both files live in the /etc directory).





I haven't looked at Apple's default settings in High Sierra, nor have I attempted to to do an in-place upgrade from older versions of macOS & OS X (i.e.; El Capitan, etc).





I typically use the folliwng SMB client settings in my environment (for accessing our EMC Isilon SMB3 storage cluster running OneFS 8.x)





[default]

streams=yes

file_ids_off=yes

signing_required=no









Hope this helps.