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Date: Tue, 28 Dec 1999 22:09:30 -0500 (EST)
From: Matt Gostick <matt@crazylogic.net>
To: freebsd-questions@freebsd.org
Subject: ioctl programming probs
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I'm trying to make a simple little program that gets the ip address of a
given interface.  I'm using ioctl to do this and am having a wierd problem
that I can't figure out.  Any help is appretiated.  

From what I understand about ioctl ... the below program should display
the interface name, ip address, destination address and the broadcast
address.  Unfortuanely it's not.  It's not crashing ... it just always 
prints:

name      : lo0
addr      : 16.2.0.0
dstaddr   : 16.2.0.0
broadaddr : 16.2.0.0

I've tried this on two different FreeBSD-3.2 machines with the same 
result, even the same IP's.  I've even tried switching the interface
names to something different, and am still getting the same IP's.

I have searched newsgroups and mailing lists only to come up with no
solution.  I was hoping that those familiar with ioctl under FreeBSD will
spot my mistake in a couple of seconds... :)  I'm new to it so any help is
very much appretiated.

/* --<get_if_ip.c>------------------------------------- */

#include <stdio.h>  
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <net/if.h>
             
int main (void) {
  int fd;
  struct ifreq ifr;
             
  /* open a socket to use for ioctl */
  if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
    perror("socket");
    return -1;
  }
     
  strcpy(ifr.ifr_name, "lo0");
  
  /* get if address */
  if (ioctl(fd, SIOCGIFADDR, &ifr, sizeof(ifr)) == -1) {
    close(fd);
    perror("ioctl");
    return -1;
  }
  
  printf("name      : %s\n", ifr.ifr_name);
  printf("addr      : %s\n", inet_ntoa(ifr.ifr_addr));   
  printf("dstaddr   : %s\n", inet_ntoa(ifr.ifr_dstaddr));  
  printf("broadaddr : %s\n", inet_ntoa(ifr.ifr_broadaddr));
  
  close(fd);
  return 0;
} 

/* --<end get_if_ip.c>---------------------------------- */


Thanks,
Matt



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