双机热备中解决IP漂移后arp表不更新

方案一  ip漂移后向用这个IP向该网段发送arp广播，促使arp表更新

方案二 用一个备用mac，ip漂移的时候连同mac一起漂移

#include <iostream>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/if_ether.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netinet/tcp.h>
#include <net/if.h>
#include <memory.h>
#include <arpa/inet.h>

using namespace std;
enum
{
	ARP_MSG_SIZE = 0x2a
};

char * strncpy_IFNAMSIZ(char * dst, const char * src)
{
# ifndef IFNAMSIZ
	enum
	{
		IFNAMSIZ = 16
	};
# endif
	return strncpy(dst, src, IFNAMSIZ);
}

struct arpMsg
{
	/* Ethernet header */
	uint8_t h_dest[6]; /* 00 destination ether addr */
	uint8_t h_source[6]; /* 06 source ether addr */
	uint16_t h_proto; /* 0c packet type ID field */

	/* ARP packet */
	uint16_t htype; /* 0e hardware type (must be ARPHRD_ETHER) */
	uint16_t ptype; /* 10 protocol type (must be ETH_P_IP) */
	uint8_t hlen; /* 12 hardware address length (must be 6) */
	uint8_t plen; /* 13 protocol address length (must be 4) */
	uint16_t operation; /* 14 ARP opcode */
	uint8_t sHaddr[6]; /* 16 sender's hardware address */
	uint8_t sInaddr[4]; /* 1c sender's IP address */
	uint8_t tHaddr[6]; /* 20 target's hardware address */
	uint8_t tInaddr[4]; /* 26 target's IP address */
	uint8_t pad[18]; /* 2a pad for min. ethernet payload (60 bytes) */
} PACKED;
const int const_int_1 = 1;
int setsockopt_broadcast(int fd)
{
	return setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &const_int_1,
			sizeof(const_int_1));
}

char * safe_strncpy(char * dst, const char * src, size_t size)
{
	if (!size)
		return dst;
	dst[--size] = '/0';
	return strncpy(dst, src, size);
}

int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t * from_mac,
		const char * interface)
{
	int timeout_ms;
	int s;
	int rv = 1; /* "no reply received" yet */
	struct sockaddr addr; /* for interface name */
	struct arpMsg arp;

	s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
	if (s == -1)
	{
		perror("raw_socket");
		return -1;
	}

	if (setsockopt_broadcast(s) == -1)
	{
		perror("cannot enable bcast on raw socket");
		goto ret;
	}

	/* send arp request */
	memset(&arp, 0, sizeof(arp));
	memset(arp. h_dest, 0xff, 6); /* MAC DA */
	memcpy(arp. h_source, from_mac, 6); /* MAC SA */
	arp. 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 */
	memcpy(arp. sHaddr, from_mac, 6); /* source hardware address */
	memcpy(arp. sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
	/* tHaddr is zero-fiiled *//* target hardware address */
	memcpy(arp. tInaddr, &test_ip, sizeof(test_ip)); /* target IP address */

	memset(&addr, 0, sizeof(addr));
	safe_strncpy(addr. sa_data, interface, sizeof(addr. sa_data));
	if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0)
	{
		// TODO: error message? caller didn't expect us to fail,
		// just returning 1 "no reply received" misleads it.
	}

	ret: close(s);
	return rv;
}

int read_interface(const char * interface, int * ifindex, uint32_t * addr,
		uint8_t * arp)
{
	int fd;
	struct ifreq ifr;
	struct sockaddr_in * our_ip;

	memset(&ifr, 0, sizeof(ifr));
	fd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);

	ifr. ifr_addr. sa_family = AF_INET;
	strncpy_IFNAMSIZ(ifr. ifr_name, interface);
	if (addr)
	{
		if (ioctl(fd, SIOCGIFADDR, &ifr) != 0)
		{
			perror("ioctl");
			close(fd);
			return -1;
		}
		our_ip = (struct sockaddr_in *) &ifr. ifr_addr;
		*addr = our_ip-> sin_addr. s_addr;
		printf("ip of %s = %s \n", interface, inet_ntoa(our_ip-> sin_addr));
	}

	if (ifindex)
	{
		if (ioctl(fd, SIOCGIFINDEX, &ifr) != 0)
		{
			close(fd);
			return -1;
		}
		printf("adapter index %d", ifr. ifr_ifindex);
		*ifindex = ifr. ifr_ifindex;
	}

	if (arp)
	{
		if (ioctl(fd, SIOCGIFHWADDR, &ifr) != 0)
		{
			close(fd);
			return -1;
		}
		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]);
	}
	close(fd);
	return 0;
}

int main(void)
{
	uint32_t TEST_IP = inet_addr("10.192.64.255");
	char interface[] = "eth0";
	uint32_t ip, t_ip;
	uint8_t mac[6];
	read_interface(interface, NULL, &ip, mac);
	char buf[128];
	strcpy(buf, "ifconfig eth0:1 10.192.64.137 netmask 255.255.255.0");
	system(buf);

	t_ip = inet_addr("10.192.64.137");
	for (int i = 0; i < 10; i++)
	{
		arpping(TEST_IP, t_ip, mac, interface);
		usleep(50);
	}
	return 0;

}