System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP)

What if the Syntax is Wrong?

Client library routines contain compiled-in default entries that are used if an entry in the nsswitch.conf file is either missing or syntactically incorrect. These entries are the same as the switch file's defaults.

The name service switch assumes that the table and source names are spelled correctly. If you misspell a table or source name, the switch uses default values.