In a config file, you can write the debugging options, a vty's password, routing daemon configurations, a log file name, and so forth. This information forms the initial command set for a routing beast as it is starting.
Config files are generally found in:
/usr/local/etc/*.conf
Each of the daemons has its own config file. For example, zebra's default config file name is:
/usr/local/etc/zebra.conf
The daemon name plus .conf is the default config file name. You
can specify a config file using the -f or --config-file
options when starting the daemon.