<tt>setsockname</tt></a> 
method <em>before</em> sending any datagrams.   Otherwise, the socket is
automatically  bound  to an  ephemeral  address  before the  first  data
transmission and once bound the local address cannot be changed.  
The   other  methods   available  for  UDP   sockets  are
<a href=udp.html#getpeername><tt>getpeername</tt></a>,  
<a href=udp.html#getsockname><tt>getsockname</tt></a>, 
<a href=udp.html#settimeout><tt>settimeout</tt></a>,
<a href=udp.html#setoption><tt>setoption</tt></a>