Set an IP address and routing in C

Submitted by admin on

If you want to set an ipaddress and route in a C program, the following code should work for you.

  1. #include <stdlib.h>
  2. #include <stdio.h>
  3. #include <string.h>
  4. #include <sys/socket.h>
  5. #include <net/if.h>
  6. #include <net/if_arp.h>
  7. #include <sys/ioctl.h>
  8. #include <linux/sockios.h>
  9. #include <errno.h>
  10. #include <netinet/in.h>
  11. #include <net/route.h>
  12. #if defined(__GLIBC__) && __GLIBC__ >=2 && __GLIBC_MINOR__ >= 1
  13. #include <netpacket/packet.h>
  14. #include <net/ethernet.h>
  15. #else
  16. #include <sys/types.h>
  17. #include <netinet/if_ether.h>
  18. #endif
  19.  
  20. /**
  21. * Create socket function
  22. */
  23. int create_socket() {
  24.  
  25.   int sockfd = 0;
  26.  
  27.   sockfd = socket(AF_INET, SOCK_DGRAM, 0);
  28.   if(sockfd == -1){
  29.     fprintf(stderr, "Could not get socket.\n");
  30.     return -1;
  31.   }
  32.  
  33.   return sockfd;
  34.  
  35. }
  36.  
  37. /**
  38. * Generic ioctrlcall to reduce code size
  39. */
  40. int generic_ioctrlcall(int sockfd, u_long *flags, struct ifreq *ifr) {
  41.  
  42.   if (ioctl(sockfd, (long unsigned int)flags, &ifr) < 0) {
  43.     fprintf(stderr, "ioctl: %s\n", (char *)flags);
  44.     return -1;
  45.   }
  46.   return 1;
  47. }
  48.  
  49. /**
  50. * Set route with metric 100
  51. */
  52. int set_route(int sockfd, char *gateway_addr,  struct sockaddr_in *addr) {
  53.  
  54.   struct rtentry route;
  55.   int err = 0;
  56.   memset(&route, 0, sizeof(route));
  57.   addr = (struct sockaddr_in*) &route.rt_gateway;
  58.   addr->sin_family = AF_INET;
  59.   addr->sin_addr.s_addr = inet_addr(gateway_addr);
  60.   addr = (struct sockaddr_in*) &route.rt_dst;
  61.   addr->sin_family = AF_INET;
  62.   addr->sin_addr.s_addr = inet_addr("0.0.0.0");
  63.   addr = (struct sockaddr_in*) &route.rt_genmask;
  64.   addr->sin_family = AF_INET;
  65.   addr->sin_addr.s_addr = inet_addr("0.0.0.0");
  66.   route.rt_flags = RTF_UP | RTF_GATEWAY;
  67.   route.rt_metric = 100;
  68.  
  69.   if ((err = ioctl(sockfd, SIOCADDRT, &route)) < 0) {
  70.     fprintf(stderr, "ioctl: %s\n", (char *)flags);
  71.     return -1;
  72.   }
  73.   return 1;
  74.  
  75. }
  76.  
  77. /**
  78. * Set ip function
  79. */
  80. int set_ip(char *iface_name, char *ip_addr, char *gateway_addr)
  81. {
  82.   if(!iface_name)
  83.     return -1;
  84.    
  85.   struct ifreq ifr;
  86.   struct sockaddr_in sin;
  87.   int sockfd = create_socket();
  88.  
  89.   sin.sin_family = AF_INET;
  90.  
  91.   // Convert IP from numbers and dots to binary notation
  92.   inet_aton(ip_addr,&sin.sin_addr.s_addr);
  93.  
  94.   /* get interface name */
  95.   strncpy(ifr.ifr_name, iface_name, IFNAMSIZ);
  96.  
  97.   /* Read interface flags */
  98.   generic_ioctrlcall(sockfd, (u_long *)"SIOCGIFFLAGS", &ifr);
  99.  
  100.   /*
  101.   * Expected in <net/if.h> according to
  102.   * "UNIX Network Programming".
  103.   */
  104.   #ifdef ifr_flags
  105.   # define IRFFLAGS       ifr_flags
  106.   #else   /* Present on kFreeBSD */
  107.   # define IRFFLAGS       ifr_flagshigh
  108.   #endif
  109.  
  110.   // If interface is down, bring it up
  111.   if (ifr.IRFFLAGS | ~(IFF_UP)) {
  112.     ifr.IRFFLAGS |= IFF_UP;
  113.     generic_ioctrlcall(sockfd, (u_long *)"SIOCSIFFLAGS", &ifr);
  114.   }
  115.  
  116.   // Set route
  117.   set_route(sockfd, gateway_addr,  &sin);
  118.  
  119.   memcpy(&ifr.ifr_addr, &sin, sizeof(struct sockaddr)); 
  120.  
  121.   // Set interface address
  122.   if (ioctl(sockfd, SIOCSIFADDR, &ifr) < 0) {
  123.     fprintf(stderr, "Cannot set IP address. ");
  124.     perror(ifr.ifr_name);
  125.     return -1;
  126.   }            
  127.   #undef IRFFLAGS
  128.  
  129.   return 0;
  130. }
  131.  
  132. void usage()
  133. {
  134.   const char *usage = {
  135.     "./set_ip [interface] [ip address] [gateway address]\n"
  136.   };
  137.   fprintf(stderr,"%s",usage);
  138. }
  139.  
  140. int main(int argc, char **argv)
  141. {
  142.   if(argc < 3){
  143.     usage();
  144.     return -1;
  145.   }else {
  146.    
  147.     set_ip(argv[1],argv[2], argv[3]);
  148.    
  149.     return 0;
  150.   }
  151. }

Adapted and modified from http://www.lainoox.com/set-ip-address-c-linux/

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