rndc.conf — rndc configuration file
rndc.conf 
        rndc.conf is the configuration file
	for rndc, the BIND 9 name server control
	utility.  This file has a similar structure and syntax to
	named.conf.  Statements are enclosed
	in braces and terminated with a semi-colon.  Clauses in
	the statements are also semi-colon terminated.  The usual
	comment styles are supported:
    
C style: /* */
C++ style: // to end of line
Unix style: # to end of line
        rndc.conf is much simpler than
	named.conf.  The file uses three
	statements: an options statement, a server statement
	and a key statement.
    
        The options statement contains three clauses.
	The default-server clause is followed by the
	name or address of a name server.  This host will be used when
	no name server is given as an argument to
	rndc.  The default-key
	clause is followed by the name of a key which is identified by
	a key statement.  If no
	keyid is provided on the rndc command line,
	and no key clause is found in a matching
	server statement, this default key will be
	used to authenticate the server's commands and responses.  The
	default-port clause is followed by the port
	to connect to on the remote name server.  If no
	port option is provided on the rndc command
	line, and no port clause is found in a
	matching server statement, this default port
	will be used to connect.
    
        After the server keyword, the server statement
	includes a string which is the hostname or address for a name
	server.  The statement has two possible clauses:
	key and port. The key name must
	match the name of a key statement in the file.  The port number
	specifies the port to connect to.
    
        The key statement begins with an identifying
	string, the name of the key.  The statement has two clauses.
	algorithm identifies the encryption algorithm
	for rndc to use; currently only HMAC-MD5 is
	supported.  This is followed by a secret clause which contains
	the base-64 encoding of the algorithm's encryption key.  The
	base-64 string is enclosed in double quotes.
    
There are two common ways to generate the base-64 string for the secret. The BIND 9 program rndc-confgen can be used to generate a random key, or the mmencode program, also known as mimencode, can be used to generate a base-64 string from known input. mmencode does not ship with BIND 9 but is available on many systems. See the EXAMPLE section for sample command lines for each.
    options {
        default-server  localhost;
        default-key     samplekey;
      };
      server localhost {
        key             samplekey;
      };
      key samplekey {
        algorithm       hmac-md5;
        secret          "c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
      };
    
In the above example, rndc will by default use the server at localhost (127.0.0.1) and the key called samplekey. Commands to the localhost server will use the samplekey key, which must also be defined in the server's configuration file with the same name and secret. The key statement indicates that samplekey uses the HMAC-MD5 algorithm and its secret clause contains the base-64 encoding of the HMAC-MD5 secret enclosed in double quotes.
To generate a random secret with rndc-confgen:
        rndc-confgen
    
        A complete rndc.conf file, including the
        randomly generated key, will be written to the standard
        output.  Commented out key and
        controls statements for
        named.conf are also printed.
    
To generate a base-64 secret with mmencode:
        echo "known plaintext for a secret" | mmencode