gateway 默认路由获取与设置

//Route add -net default gw 192.168.22.1
//在有IP没有默认路由的时候设置

/*cat /proc/net/route
Iface   Destination     Gateway         Flags   RefCnt  Use     Metric  Mask            MTU     Window  IRTT                                                      
eth0    0016A8C0        00000000        0001    0       0       0       00FFFFFF        0       0       0                                                                              
eth0    00000000        0116A8C0        0003    0       0       0       00000000        0       0       0  
*/
#include  
#include  
#include  
#include  
#include
#include
#include  
#include  
#include
#include  
#include  
#include  

int network_get_gatway(int sock_id,char *interface_name, char *gateway)
{
 FILE *fp;   
 char buf[256]; // 128 is enough for linux   
 char iface[16];   
 unsigned long dest_addr,net_addr,gate_addr;  
 struct in_addr addr;
 unsigned long *p;

 fp = fopen("/proc/net/route", "r");   
 if (fp == NULL)   
  return -1;   
 /* Skip title line */   
 fgets(buf, sizeof(buf), fp);   
 while (fgets(buf, sizeof(buf), fp))
 {   
  if (sscanf(buf, "%s\t%lX\t%lX", iface,&dest_addr, &gate_addr)!= 3||dest_addr != 0||!strcpy(iface,interface_name))   
   continue;   
  break;   
 }   
 
 fclose(fp); 
 printf("gate_addr:%lx\n",gate_addr);
 memcpy(&addr,&gate_addr,4);
 strcpy( gateway,inet_ntoa(addr));
 printf("gateway=%s\n",gateway);
 return 0;   

}

int network_set_getway(int sock_id,char *interface_name, char *gateway)
{
 struct rtentry rt;
 u_int32_t dstaddr, gwaddr;

 dstaddr = inet_addr("0.0.0.0");
 gwaddr = inet_addr(gateway);
 
 memset (&rt, 0, sizeof (rt));
 
 /*set Destination addr*/
 memset ((char *) &(rt.rt_dst),0, sizeof(rt.rt_dst));
 rt.rt_dst.sa_family = AF_INET;
 ((struct sockaddr_in *)&(rt.rt_dst))->sin_addr.s_addr= dstaddr;
  
 /*set gw addr*/
 memset ((char *) &(rt.rt_gateway),0, sizeof(rt.rt_gateway));
 rt.rt_gateway.sa_family = AF_INET;
 ((struct sockaddr_in *)&(rt.rt_gateway))->sin_addr.s_addr= gwaddr;

 
 /*set genmask addr*/
 memset ((char *) &(rt.rt_genmask),0, sizeof(rt.rt_genmask));
 rt.rt_genmask.sa_family = AF_INET;
 ((struct sockaddr_in *)&(rt.rt_genmask))->sin_addr.s_addr= 0L;
 
 
 rt.rt_dev = interface_name;
 rt.rt_flags = RTF_GATEWAY;
 
 if (ioctl(sock_id, SIOCADDRT, &rt) < 0)
 {
  printf("SIOCADDRT failed: %s %d\n", strerror(errno),RTF_GATEWAY);
  return -1;
 }
 
 return 0;
}

int main()
{
 int sock_id;
 char ifname[]="eth0";
 char getway[16]="192.168.22.1";
 char getway1[16];
 
 sock_id=socket(AF_INET,SOCK_DGRAM,0);
 if (sock_id < 0)
 {
  printf("socket failed: %s\n", strerror(errno));
  return -1;
 }
 
 network_set_getway(sock_id,ifname, getway);
 network_get_gatway(sock_id,ifname, getway1);
 
 
 return 0;
}