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 <stdio.h> 

#include <stdlib.h> 

#include <unistd.h> 

#include <string.h> 

#include <errno.h>

#include <sys/ioctl.h>

#include <netinet/in.h> 

#include <net/route.h> 

#include <net/if.h>

#include <sys/socket.h> 

#include <sys/types.h> 

#include <arpa/inet.h> 

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;

}