检测原理
发送ARP包判断网络内是否有相应的应答。有对应的应答则ip地址已经被其他设备使用，超时无应答则无冲突。
根据简书陈兄抓的包的情况看，询问ip是否被占用时需要发送一个源IP为0.0.0.0，目的IP为查询ip的arp包。具体代码如下
检测代码
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <arpa/inet.h>
#define MAC_BCAST_ADDR (unsigned char *) "/xff/xff/xff/xff/xff/xff"
#define ETH_INTERFACE "eth0"
#define ARP_MSG_SIZE 0x2a
struct arpMsg
{
struct ethhdr ethhdr; /* Ethernet header */
u_short htype; /* hardware type (must be ARPHRD_ETHER) */
u_short ptype; /* protocol type (must be ETH_P_IP) */
u_char hlen; /* hardware address length (must be 6) */
u_char plen; /* protocol address length (must be 4) */
u_short operation; /* ARP opcode */
u_char sHaddr[6]; /* sender's hardware address */
u_char sInaddr[4]; /* sender's IP address */
u_char tHaddr[6]; /* target's hardware address */
u_char tInaddr[4]; /* target's IP address */
u_char pad[18]; /* pad for min. Ethernet payload (60 bytes) */
};
/*获取eth0的ip地址和mac地址*/
int geteth0(u_int32_t *ip, unsigned char *mac)
{
int fd;
struct ifreq ifr;
struct sockaddr_in *addr;
if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) >= 0)
{
strncpy(ifr.ifr_name, "eth0", IFNAMSIZ);
ifr.ifr_name[IFNAMSIZ - 1] = '\0';
if (ioctl(fd, SIOCGIFADDR, &ifr) == 0)
{
addr = (struct sockaddr_in *) & (ifr.ifr_addr);
*ip = addr->sin_addr.s_addr;
}
else
{
close(fd);
return -1;
}
if (ioctl(fd, SIOCGIFHWADDR, &ifr) == 0)
{
memcpy(mac, ifr.ifr_hwaddr.sa_data, 6);
}
else
{
return -1;
}
}
else
{
perror("getIpAddr error :");
return -1;
}
close(fd);
return 0;
}
/*参数说明 目标IP地址，本机IP地址，本机mac地址，网卡类型*/
int arpping(u_int32_t desIp, u_int32_t srcIp, unsigned char *mac, char *interface)
{
int optval = 1;
int fd; /* socket */
int ret = 1; /* return value */
struct sockaddr addr; /* for interface name */
struct arpMsg arp;
fd_set fdset;
struct timeval tm;
int len = 0;
/*socket发送一个arp包*/
if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) == -1)
{
printf("Could not open raw socket\n");
return -1;
}
/*设置套接口类型为广播，把这个arp包是广播到这个局域网*/
if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &optval, sizeof(optval)) == -1)
{
printf("Could not setsocketopt on raw socket\n");
close(fd);
return -1;
}
memset(&arp, 0, sizeof(arp));
memcpy(arp.ethhdr.h_dest, MAC_BCAST_ADDR, 6); /* MAC DA */
memcpy(arp.ethhdr.h_source, mac, 6); /* MAC SA */
arp.ethhdr.h_proto = htons(ETH_P_ARP); /* protocol type (Ethernet) */
arp.htype = htons(ARPHRD_ETHER); /* hardware type */
arp.ptype = htons(ETH_P_IP); /* protocol type (ARP message) */
arp.hlen = 6; /* hardware address length */
arp.plen = 4; /* protocol address length */
arp.operation = htons(ARPOP_REQUEST); /* ARP op code */
*((u_int *) arp.sInaddr) = srcIp; /* source IP address */
memcpy(arp.sHaddr, mac, 6); /* source hardware address */
*((u_int *) arp.tInaddr) = desIp; /* target IP address */
memset(&addr, 0, sizeof(addr));
strcpy(addr.sa_data, interface);
/*发送arp请求*/
if (sendto(fd, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0)
ret = -2;
tm.tv_sec = 2;
tm.tv_usec = 0;
FD_ZERO(&fdset);
FD_SET(fd, &fdset);
while (1)
{
if (select(fd + 1, &fdset, NULL, NULL, &tm) <= 0)
{
//printf("timeout\n"); //超时算没有冲突
break;
}
else if (FD_ISSET(fd, &fdset))
{
if ((len = recv(fd, &arp, sizeof(arp), 0)) < 0)
{
ret = 0;
}
// if(len>=ARP_MSG_SIZE) //这里会接收到其他arp包
// {
// u_int32_t tmp = *((u_int *) arp.sInaddr);
// printf("ip=%d.%d.%d.%d\n",tmp&0xff,(tmp>>8)&0xff,(tmp>>16)&0xff,tmp>>24);
// }
/*如果条件 htons(ARPOP_REPLY) bcmp(arp.tHaddr, mac, 6) == 0 *((u_int *) arp.sInaddr) == desIp
三者都为真，则ARP应答有效,说明这个地址是已近存在的*/
if (arp.operation == htons(ARPOP_REPLY) &&
bcmp(arp.tHaddr, mac, 6) == 0 &&
*((u_int *) arp.sInaddr) == desIp)
{
printf("Valid arp reply receved for this mac address=%02x:%02x:%02x:%02x:%02x:%02x\n",
arp.sHaddr[0], arp.sHaddr[1], arp.sHaddr[2], arp.sHaddr[3], arp.sHaddr[4], arp.sHaddr[5]);
ret = 0;
break;
}
}
}
close(fd);
return ret;
}
int test_check_myself_ip()
{
int ret = -1;
u_int32_t ip = 0;
unsigned char mac[6] = {0};
if (geteth0(&ip, mac))
{
printf("get eth0 error\n");
return -1;
}
ret = arpping(ip, 0, mac, "eth0"); //将ip替换为需要检测的ip，这里检测本机。
if (ret == 0)
{
printf("conflict-->\n");
}
else if (ret == 1)
{
printf("no conflict-->\n");
}
else
{
printf("arping error\n");
}
return 0;
}
int main(int argc, char *argv[])
{
test_check_myself_ip();
return 0;
}
参考网站
1- 图解ARP协议（五）免费ARP：地址冲突了肿么办？
2- linux下检测ip冲突
3- Linux下IP冲突检测程序源码及分析(利用免费arp)—感谢原作者