In message <46979972.8000406@cat.co.za>
	on Fri, 13 Jul 2007 17:25:38 +0200,
	Ian McIntosh <ianm@cat.co.za> wrote:
> Stevens Network Programming vol 1 says in section 18.2 Broadcast Addresses
> (p. 471):
> 
> "Most hosts allow [sending a UDP datagram to 255.255.255.255] [...] and
> convert the address to the subnet-directed broadcast address of the
> outgoing interface. BSD/OS has [...] IP_ONESBCAST, and when set, the
> destination IP address for broadcasts is 255.255.255.255 [...]"
> 
> NetBSD doesn't have this option, so how do we do it?
in_pcbconnect() in sys/netinet/in_pcb.c, there are these code gragments.

	if (TAILQ_FIRST(&in_ifaddrhead) != 0) {
		/*
		 * If the destination address is INADDR_ANY,
		 * use any local address (likely loopback).
		 * If the supplied address is INADDR_BROADCAST,
		 * use the broadcast address of an interface
		 * which supports broadcast. (loopback does not)
		 */

		if (in_nullhost(sin->sin_addr)) {
			sin->sin_addr =
			    TAILQ_FIRST(&in_ifaddrhead)->ia_addr.sin_addr;
		} else if (sin->sin_addr.s_addr == INADDR_BROADCAST) {
			TAILQ_FOREACH(ia, &in_ifaddrhead, ia_list) {
				if (ia->ia_ifp->if_flags & IFF_BROADCAST) {
					sin->sin_addr =
					    ia->ia_broadaddr.sin_addr;
					break;
				}
			}
		}
		...

I don't know when this code exists, but maybe it is after 4.3BSD and
it seems that NetBSD has this code from revision 1.1.

-- 
Takahiro Kambe <taca@back-street.net>