Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!racerx!ken
From: ken@racerx.UUCP (Ken Hardy)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Internet broadcast: INADDR_BROADCAST
Summary: Need valid net portion
Message-ID: <567@racerx.UUCP>
Date: 11 Apr 91 18:00:45 GMT
References: <BENNY.91Apr10110956@dimona.vlss.amdahl.com>
Distribution: comp
Organization: Bridge Information Systems, St. Louis
Lines: 71

In article <BENNY.91Apr10110956@dimona.vlss.amdahl.com>, benny@vlss.amdahl.com (Benny Schnaider) writes:
> Hi,
> 
> I am trying to broadcast a message over the internet by using the
> INADDR_BROADCAST shorthand notation. I tried this on SunOS 4.01
> and got: Network is unreachable... On other system that I tried
> the same code it worked.
> Code is enclosed.
> 
> 1. What is the problem ?
> 2. How common is it to use INADDR_BROADCAST ?
> 
> Thanks,
> Benny.


You need to have a valid network in the network portion of
the internet address.  This is a routine I use on Suns to
build a broadcast address.  May not be cleanest code, but
it works on Sun 4.0 & 4.1.  The print statements yield:

		Name = [racerx]
		Host ID 80420006
		Net  ID 00008042
		Bcast ID 8042ffff

This get physically resolved on our system to a broadcast ethernet
address.  This may or may not be passed by bridges.  IP routers
may not pass it based on the network portion of the IP address,
and even if a bridge or router passes it, other IP hosts on another
network may not pay attention to it if they have another network
i.d.


----------------------------------------------------------------

int     bcast_address ()
/*
 *
 */
{
    struct in_addr bcip;
    unsigned ipad,
            netp;
    extern struct hostent *getmyhostent () ;


    if (my_he == (struct hostent *)0)
    {
        my_he = getmyhostent () ;
        memcpy (&myip.s_addr, my_he->h_addr, sizeof (myip.s_addr));
        memcpy (&my_ipaddr[0], my_he->h_addr, sizeof (myip.s_addr) ) ;
    }
    netp = inet_netof (myip);
    bcip = inet_makeaddr (netp, INADDR_BROADCAST);
    if (bug)
    {
        printf ("Name = [%s]\n", my_he->h_name);
        printf ("Host ID %08lx\n", htonl (myip.s_addr));
        printf ("Net  ID %08lx\n", netp);
        printf ("Bcast ID %08lx\n", htonl (bcip.s_addr));
    }

    RETURN (bcip.s_addr);
}

----------------------------------------------------------------


-- 
Ken Hardy		uunet!racerx!ken		ken@racerx.UUCP