ONC+ Developer's Guide

Broadcast RPC

When an RPC broadcast is issued, a message is sent to all rpcbind daemons on a network. An rpcbind daemon with which the requested service is registered forwards the request to the server. The main differences between broadcast RPC and normal RPC calls are:

The following code example shows how rpc_broadcast() is used and describes its arguments.

Example 5–2 RPC Broadcast

 * bcast.c: example of RPC broadcasting use.
#include <stdio.h>
#include <rpc/rpc.h>
main(argc, argv)
	int argc;
	char *argv[];
	enum clnt_stat rpc_stat;
	rpcprog_t prognum;
	rpcvers_t vers;
	struct rpcent *re;
	if(argc != 3) {
		fprintf(stderr, "usage : %s RPC_PROG VERSION\n", argv[0]);
	if (isdigit( *argv[1]))
		prognum = atoi(argv[1]);
	else {
		re = getrpcbyname(argv[1]);
		if (! re) {
			fprintf(stderr, "Unknown RPC service %s\n", argv[1]);
		prognum = re->r_number;
	vers = atoi(argv[2]);
	rpc_stat = rpc_broadcast(prognum, vers, NULLPROC, xdr_void,
	           (char *)NULL, xdr_void, (char *)NULL, bcast_proc,
	if ((rpc_stat != RPC_SUCCESS) && (rpc_stat != RPC_TIMEDOUT)) {
		fprintf(stderr, "broadcast failed: %s\n",

The function in Example 5–3 collects the replies to the broadcast. The normal operation is to collect either the first reply or all replies. bcast_proc() displays the IP address of the server that has responded. Because the function returns FALSE it continues to collect responses. The RPC client code continues to resend the broadcast until it times out.

Example 5–3 Collect Broadcast Replies

bcast_proc(res, t_addr, nconf)
	void *res;									/* Nothing comes back */
	struct t_bind *t_addr;					/* Who sent us the reply */
	struct netconfig *nconf;
	register struct hostent *hp;
	char *naddr;

	naddr = taddr2naddr(nconf, &taddr->addr);
	if (naddr == (char *) NULL) {
		fprintf(stderr,"Responded: unknown\n");
	} else {
		fprintf(stderr,"Responded: %s\n", naddr);

If done is TRUE, then broadcasting stops and rpc_broadcast() returns successfully. Otherwise, the routine waits for another response. The request is rebroadcast after a few seconds of waiting. If no responses come back, the routine returns with RPC_TIMEDOUT.