The sites-available, sites-enabled convention has been
borrowed from Apache, Nginx, and other similar projects.
As of FreeRADIUS 2.x.x virtual servers are located in the
raddb/sites-available subdirectory of the main configuration
directory. Each of these files contains a server <name> {}
stanza to declare a server configuration, which may then contain a
listen {} stanza to bind that server to a given ip/port.
The files from raddb/sites-available are symbolically linked
(symlinked) from the raddb/sites-enabled directory. This
allows the administrator to selectively enable and disable virtual
servers.
Every file in raddb/sites-enabled is $INCLUDE'd from
radiusd.conf.
