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Version 2 (modified by Vdcappel, on 04/14/08 at 17:17:45) (diff)

Added code to obtain MAC address

Obtaining Interface Information

This is based on an answer posted to the RTEMS User's mailing list by ThomasRauscher?, updated with an answer posted by Arnout Vandecappelle?

Question: What is the best way to obtain my IP address, MAC Address, Network Mask, and Default Gateway after the rtemsbsdnetinitializenetwork()_ call? I want to be able to access this information from software.

Answer: The following code retrieves the IP address for an interface. 'ifname' should contain the name of your interface, e.g. "eth0", 'addr' then contains the result. Replace _SIOCGIFADDR_ by _SIOCGIFBRDADDR_ for the broadcast address, _SIOCGIFNETMASK_ for the net mask, and _SIOCGIFDSTADDR_ for the other side of a point-to-point link.

#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <net/if.h>
#include <netinet/in.h>

int get_ifaddr(const char *ifname, struct in_addr *addr)
    int fd;
    int rc;
    struct ifreq ifreq;
    struct sockaddr_in *sockaddr;

    fd = socket(AF_INET, SOCK_DGRAM, 0);
    if(fd<0) {
        return -1;

    strcpy(ifreq.ifr_name, ifname);

    rc = ioctl(fd, SIOCGIFADDR, &ifreq);
    if(rc == 0)
        sockaddr = (struct sockaddr_in *) &ifreq.ifr_ifru.ifru_addr;
        memcpy(addr, &sockaddr->sin_addr, sizeof(*addr));

    return (rc==0) ? 0 : -1;

Finding the MAC address is a little more complex. The code below does the trick. 'ifname' should contain the name of your interface, e.g. "eth0", 'addr' then contains the result. 'addr' should be pre-allocated and large enough to store the Ethernet address (i.e. 6 bytes).

Note that it is necessary to hard-code the number 18 because the AF_LINK definition is not visible outside of the bsdnet kernel.

#include <sys/socket.h>  /* For sockaddr */
#include <net/if.h>      /* For struct ifreq, required by SIO* */
#include <net/if_types.h> /* For IFT_ETHER */
#include <net/if_dl.h>    /* For sockaddr_dl */
#include <sys/sockio.h>  /* For SIO* */

int get_macaddr(const char *ifname, char *addr)
  int i;
  char buf[1024];
  int sock;
  struct ifconf ifc;
  struct ifreq *ifr, *lifr;
  struct sockaddr_dl *sdl;

  ifc.ifc_buf = buf;
  ifc.ifc_len = sizeof(buf);

  if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
    return sock;
  i =  ioctl(sock, SIOCGIFCONF, (char *)&ifc);
  if (i < 0) {
    return i;

  ifr = ifc.ifc_req;
  lifr = (struct ifreq *)&ifc.ifc_buf[ifc.ifc_len];

  while (ifr < lifr) {
    struct sockaddr *sa;
    sa = &ifr->ifr_addr;
    if (!strcmp(ifr->ifr_name, ifname)) {
      sdl = (struct sockaddr_dl *)sa;
      if (sdl->sdl_family == 18) { /* AF_LINK is made invisiable in socket.h */
        memcpy (addr, LLADDR(sdl), sdl->sdl_alen);
        return sdl->sdl_alen;
    if (sa->sa_len < sizeof(*sa))
      ifr = (struct ifreq *)(((char *)sa) + sizeof(*sa));
      ifr = (struct ifreq *)(((char *)sa) + sa->sa_len);
  return -1;

For the default gateway, no simple solution is found yet.