Broadcast RPC

rpcbind is a daemon that converts RPC program numbers into network addresses comprehensible to any transport provider. rpcbind supports broadcast RPC. These are the main differences between broadcast RPC and normal RPC calls:

• Normal RPC expects one answer, whereas broadcast RPC expects many answers (one or more answer from each responding machine).

• Broadcast RPC can only be performed on connectionless protocols that support broadcasting, such as UDP.

• The implementation of broadcast RPC treats all unsuccessful responses as garbage by filtering them out. Thus, if there is a version mismatch between the broadcaster and a remote service, the user of broadcast RPC never knows.

• All broadcast messages are sent to rpcbind's network address. Thus, only services that register themselves with rpcbind are accessible via the broadcast RPC mechanism.

• The size of broadcast requests is limited to the MTU (Maximum Transfer Unit) of the local network. For Ethernet, the MTU is 1500 bytes.

   #include <rpc/clnt.h>
   #include <rpc/rpcb_clnt.h>
   	. . .
   enum clnt_stat	clnt_stat;
   	. . .
   clnt_stat = rpc_broadcast(prognum, versnum, procnum,
     inproc, in, outproc, out, eachresult, nettype)
   	u_long    prognum;        /* program number */
   	u_long    versnum;        /* version number */
   	u_long    procnum;        /* procedure number */
   	xdrproc_t inproc;         /* xdr routine for args */
   	caddr_t   in;             /* pointer to args */
   	xdrproc_t outproc;        /* xdr routine for results */
   	caddr_t   out;            /* pointer to results */
   	resultproc_t   eachresult;/* call with each result gotten */
   	char      *nettype;       /* transport type */

   bool_t done;
   	. . .
   done = eachresult(resultsp, raddr, nconf)
   	caddr_t resultsp;
   	struct netbuf *addr;     /* Addr of responding machine */
   	struct netconfig *nconf; /* Transport which responded */