由于没有找到源代码的原作者， 所以就给出一个间接的转载地址：http://blog.csdn.net/wanxiao009/article/details/5622296， 再次感谢源代码原作者
该程序运行在linux环境下，可以检测ip冲突， 我试过， 挺靠谱的，现摘录如下：(该程序涉及免费arp， 关于免费arp的概念和原理， 请自己在网上学习)
#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"
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) */
};
struct server_config_t {
u_int32_t server; /* Our IP, in network order */
u_int32_t start; /* Start address of leases, network order */
u_int32_t end; /* End of leases, network order */
struct option_set *options; /* List of DHCP options loaded from the config file */
char *interface; /* The name of the interface to use */
int ifindex; /* Index number of the interface to use */
unsigned char arp[6]; /* Our arp address */
unsigned long lease; /* lease time in seconds (host order) */
unsigned long max_leases; /* maximum number of leases (including reserved address) */
char remaining; /* should the lease file be interpreted as lease time remaining, or
* as the time the lease expires */
unsigned long auto_time; /* how long should udhcpd wait before writing a config file.
* if this is zero, it will only write one on SIGUSR1 */
unsigned long decline_time; /* how long an address is reserved if a client returns a
* decline message */
unsigned long conflict_time; /* how long an arp conflict offender is leased for */
unsigned long offer_time; /* how long an offered address is reserved */
unsigned long min_lease; /* minimum lease a client can request*/
char *lease_file;
char *pidfile;
char *notify_file; /* What to run whenever leases are written */
u_int32_t siaddr; /* next server bootp option */
char *sname; /* bootp server name */
char *boot_file; /* bootp boot file option */
};
struct server_config_t server_config;
/*参数分别表示 网卡设备类型 接口检索索引 主机IP地址 主机arp地址*/
int read_interface(char *interface, int *ifindex, u_int32_t *addr, unsigned char *arp)
{
int fd;
/*ifreq结构定义在/usr/include/net/if.h，用来配置ip地址，激活接口，配置MTU等接口信息的。
其中包含了一个接口的名字和具体内容——（是个共用体，有可能是IP地址，广播地址，子网掩码，MAC号，MTU或其他内容）。
ifreq包含在ifconf结构中。而ifconf结构通常是用来保存所有接口的信息的。
*/
struct ifreq ifr;
struct sockaddr_in *our_ip;
memset(&ifr, 0, sizeof(struct ifreq));
/*建立一个socket函数，SOCK_RAW是为了获取第三个参数的IP包数据，
IPPROTO_RAW提供应用程序自行指定IP头部的功能。
*/
if((fd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) >= 0) {
ifr.ifr_addr.sa_family = AF_INET;
/*将网卡类型赋值给ifr_name*/
strcpy(ifr.ifr_name, interface);
if (addr) {
/*SIOCGIFADDR用于检索接口地址*/
if (ioctl(fd, SIOCGIFADDR, &ifr) == 0) {
/*获取本机IP地址，addr是一个指向该地址的指针*/
our_ip = (struct sockaddr_in *) &ifr.ifr_addr;
*addr = our_ip->sin_addr.s_addr;
printf("%s (our ip) = %s/n", ifr.ifr_name, inet_ntoa(our_ip->sin_addr));
} else {
printf("SIOCGIFADDR failed, is the interface up and configured?: %s/n",
strerror(errno));
return -1;
}
}
/*SIOCGIFINDEX用于检索接口索引*/
if (ioctl(fd, SIOCGIFINDEX, &ifr) == 0) {
printf("adapter index %d/n", ifr.ifr_ifindex);
/*指针ifindex 获取索引*/
*ifindex = ifr.ifr_ifindex;
} else {
printf("SIOCGIFINDEX failed!: %s/n", strerror(errno));
return -1;
}
/*SIOCGIFHWADDR用于检索硬件地址*/
if (ioctl(fd, SIOCGIFHWADDR, &ifr) == 0) {
/*所获取的硬件地址复制到结构server_config的数组arp[6]参数中*/
memcpy(arp, ifr.ifr_hwaddr.sa_data, 6);
printf("adapter hardware address %02x:%02x:%02x:%02x:%02x:%02x/n",
arp[0], arp[1], arp[2], arp[3], arp[4], arp[5]);
} else {
printf("SIOCGIFHWADDR failed!: %s/n", strerror(errno));
return -1;
}
}
else {
printf("socket failed!: %s/n", strerror(errno));
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 yiaddr, u_int32_t ip, unsigned char *mac, char *interface)
{
int timeout = 2;
int optval = 1;
int s; /* socket */
int rv = 1; /* return value */
struct sockaddr addr; /* for interface name */
struct arpMsg arp;
fd_set fdset;
struct timeval tm;
time_t prevTime;
/*socket发送一个arp包*/
if ((s = 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(s, SOL_SOCKET, SO_BROADCAST, &optval, sizeof(optval)) == -1) {
printf("Could not setsocketopt on raw socket/n");
close(s);
return -1;
}
/* 对arp设置，这里按照arp包的封装格式赋值即可，详见http://blog.csdn.net/wanxiao009/archive/2010/05/21/5613581.aspx */
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) = ip; /* source IP address */
memcpy(arp.sHaddr, mac, 6); /* source hardware address */
*((u_int *) arp.tInaddr) = yiaddr; /* target IP address */
memset(&addr, 0, sizeof(addr));
strcpy(addr.sa_data, interface);
/*发送arp请求*/
if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0)
rv = 0;
/* 利用select函数进行多路等待*/
tm.tv_usec = 0;
time(&prevTime);
while (timeout > 0) {
FD_ZERO(&fdset);
FD_SET(s, &fdset);
tm.tv_sec = timeout;
if (select(s + 1, &fdset, (fd_set *) NULL, (fd_set *) NULL, &tm) < 0) {
printf("Error on ARPING request: %s/n", strerror(errno));
if (errno != EINTR) rv = 0;
} else if (FD_ISSET(s, &fdset)) {
if (recv(s, &arp, sizeof(arp), 0) < 0 )
rv = 0;
/*如果条件 htons(ARPOP_REPLY) bcmp(arp.tHaddr, mac, 6) == 0 *((u_int *) arp.sInaddr) == yiaddr 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) == yiaddr) {
printf("Valid arp reply receved for this address/n");
rv = 0;
break;
}
}
timeout -= time(NULL) - prevTime;
time(&prevTime);
}
close(s);
return rv;
}
int check_ip(u_int32_t addr)
{
struct in_addr temp;
if (arpping(addr, server_config.server, server_config.arp, ETH_INTERFACE) == 0)
{
temp.s_addr = addr;
printf("%s belongs to someone, reserving it for %ld seconds/n",
inet_ntoa(temp), server_config.conflict_time);
return 1;
}
else
return 0;
}
int main(int argc, char *argv[])
{
if(argc < 2)
{
printf("Usage: checkip ipaddr/n");
exit(0);
}
/*读以太网接口函数，获取一些配置信息*/
if (read_interface(ETH_INTERFACE, &server_config.ifindex,
&server_config.server, server_config.arp) < 0)
{
exit(0);
}
/*IP检测函数*/
if(check_ip(inet_addr(argv[1])) == 0)
{
printf("IP:%s can use/n", argv[1]);
}
else
{
printf("IP:%s conflict/n", argv[1]);
}
return 0;
}
再次， 真心赞一个原作者
