相关定义
ARP条目相关操作的定义
/* include/linux/sockios.h */
/* ARP cache control calls. */
/* 0x8950 - 0x8952 * obsolete calls, don't re-use */
#define SIOCDARP 0x8953 /* delete ARP table entry */
#define SIOCGARP 0x8954 /* get ARP table entry */
#define SIOCSARP 0x8955 /* set ARP table entry */ARP条目操作的结构与相关标志
/* include/linux/if_arp.h */
/* ARP ioctl request. */
struct arpreq {
struct sockaddr arp_pa; /* protocol address */
struct sockaddr arp_ha; /* hardware address */
int arp_flags; /* flags */
struct sockaddr arp_netmask; /* netmask (only for proxy arps) */
char arp_dev[16];
};
/* ARP Flag values. */
#define ATF_COM 0x02 /* completed entry (ha valid) */
#define ATF_PERM 0x04 /* permanent entry */
#define ATF_PUBL 0x08 /* publish entry */
#define ATF_USETRAILERS 0x10 /* has requested trailers */
#define ATF_NETMASK 0x20 /* want to use a netmask (only
for proxy entries) */
#define ATF_DONTPUB 0x40 /* don't answer this addresses */SIOCDARP/SIOCGARP/SIOCSARP作为ioctl(2)的第2个参数，分别用于在ARP表中删除/获取/添加单个条目
struct arpreq结构地址作为ioctl(2)的第3个参数；执行操作时，arp_pa被转换为IPv4套接字地址结构(struct sockaddr_in)，表示目的端的IP地址；arp_ha为通用套接字地址结构，sa_family为AF_UNSPEC，sa_data中包含网络接口的2层地址，如以太网mac地址，表示目的端的2层地址；arp_flags用于指定ARP操作的标志；arp_netmask用于代理ARP；arp_dev用于指定本地网络接口的名称
获取ARP条目时，需要初始化arp_pa，arp_dev，然后调用ioctl(SIOCGARP)，成功返回后arp_pa中包含的IP地址对应的mac地址保存在arp_ha.sa_data中；若指定的网络接口不存在，或存在但与指定的目标主机IP地址不对应，则ioctl以”(ENXIO)No such device or address”错误调用失败
无法通过ioctl操作获取整个ARP表，arp(8)命令的-a选项是通过读取系统中的/proc/net/arp文件内容实现该目的
添加ARP条目时，需要同时初始化arp_pa，arp_dev，arp_ha.sa_data以及arp_flags，然后调用ioctl(SIOCSARP)
删除ARP条目时，需要初始化arp_pa，arp_dev，然后调用ioctl(SIOCDARP)，成功返回后，指定目标地址对应的ARP条目被删除；若指定的网络接口不存在，或存在但与指定的目标主机IP地址不对应，则ioctl以”(ENXIO)No such device or address”错误调用失败
示例程序
系统双网卡，名称分别为eth0与eth1
初始的ARP表内容为：
# arp -n
Address HWtype HWaddress Flags Mask Iface
192.168.56.254 ether 00:50:56:f8:57:2f C eth0
192.168.56.2 ether 00:50:56:f4:a3:a0 C eth0
192.168.56.1 ether 00:50:56:c0:00:08 C eth01 . 指定本地网络接口名称与目标主机IP地址作为参数，获取对应的mac地址
/* get_arp_entry_ioctl.c */
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <net/if_arp.h>
static void get_arp_entry(const char *, const char *);
int main(int argc, char *argv[])
{
if (argc != 3) {
fprintf(stderr,
"Usage: %s [local interface name] [dst ip addres]\n", argv[0]);
exit(EXIT_FAILURE);
}
char ifname[IFNAMSIZ] = {'\0'};
strncpy(ifname, argv[1], IFNAMSIZ-1);
char ipaddr[INET_ADDRSTRLEN] = {'\0'};
strncpy(ipaddr, argv[2], INET_ADDRSTRLEN);
get_arp_entry(ifname, ipaddr);
return 0;
}
static void get_arp_entry(const char *dev, const char *ip)
{
int sfd, saved_errno, ret;
unsigned char *mac;
struct arpreq arp_req;
struct sockaddr_in *sin;
sin = (struct sockaddr_in *)&(arp_req.arp_pa);
memset(&arp_req, 0, sizeof(arp_req));
sin->sin_family = AF_INET;
inet_pton(AF_INET, ip, &(sin->sin_addr));
strncpy(arp_req.arp_dev, dev, IFNAMSIZ-1);
sfd = socket(AF_INET, SOCK_DGRAM, 0);
saved_errno = errno;
ret = ioctl(sfd, SIOCGARP, &arp_req);
if (ret < 0) {
fprintf(stderr, "Get ARP entry failed : %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
errno = saved_errno;
if (arp_req.arp_flags & ATF_COM) {
mac = (unsigned char *)arp_req.arp_ha.sa_data;
printf("MAC: %02x:%02x:%02x:%02x:%02x:%02x\n",
mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
} else {
printf("MAC: Not in the ARP cache.\n");
}
}编译并运行
# gcc get_arp_entry_ioctl.c -g3 -DC=-5 -o get_arp_entry_ioctl
#
# ./get_arp_entry_ioctl eth0 192.168.56.1
MAC: 00:50:56:c0:00:08
#
# ./get_arp_entry_ioctl eth1 192.168.56.1
Get ARP entry failed : No such device or address
#
# ./get_arp_entry_ioctl eth1 192.168.56.100
Get ARP entry failed : No such device or address2 . 指定本地网络接口名称，目标主机IP地址与mac地址作为参数，添加ARP条目
/* set_arp_entry_ioctl.c */
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <net/if_arp.h>
static void set_arp_entry(char *, char *, char *);
static int parse_mac(char *, char *);
int main(int argc, char *argv[])
{
if (argc != 4) {
fprintf(stderr,
"Usage: %s [local interface name] [dst ip addres] [dst mac address]\n",
argv[0]);
exit(EXIT_FAILURE);
}
char ifname[IFNAMSIZ] = {'\0'};
strncpy(ifname, argv[1], IFNAMSIZ-1);
char ipaddr[INET_ADDRSTRLEN] = {'\0'};
strncpy(ipaddr, argv[2], INET_ADDRSTRLEN);
int mac_size = strlen(argv[3]);
unsigned char *macaddr = (unsigned char *)malloc(mac_size);
memcpy(macaddr, argv[3], mac_size);
set_arp_entry(ifname, ipaddr, macaddr);
printf("Adding an arp entry done.\n");
return 0;
}
static void set_arp_entry(char *dev, char *ip, char *mac)
{
int sfd, saved_errno, ret;
struct arpreq arp_req;
struct sockaddr_in *sin;
sfd = socket(AF_INET, SOCK_DGRAM, 0);
sin = (struct sockaddr_in *)&(arp_req.arp_pa);
memset(&arp_req, 0, sizeof(arp_req));
sin->sin_family = AF_INET;
inet_pton(AF_INET, ip, &(sin->sin_addr));
strncpy(arp_req.arp_dev, dev, IFNAMSIZ-1);
parse_mac(mac, arp_req.arp_ha.sa_data);
arp_req.arp_flags = ATF_PERM | ATF_COM;
saved_errno = errno;
ret = ioctl(sfd, SIOCSARP, &arp_req);
if (ret < 0) {
fprintf(stderr, "Set ARP entry failed : %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
errno = saved_errno;
}
static int parse_mac(char *mac, char *dst)
{
int i;
unsigned byte;
char *s;
i = 0;
while ((s = strsep(&mac, ":")) != NULL) {
if (sscanf(s, "%x", &byte) != 1 || byte > 0xff)
return -1;
*(dst+i) = byte;
i++;
}
if (i != ETH_ALEN) {
fprintf(stderr, "Invalid mac address\n");
exit(EXIT_FAILURE);
}
return 0;
}编译并运行
# gcc set_arp_entry_ioctl.c -g3 -DC=-5 -o set_arp_entry_ioctl
#
# ./set_arp_entry_ioctl eth0 192.168.56.100 aa:bb:cc:dd:ee:ff
Adding an arp entry done.
#
# ./get_arp_entry_ioctl eth0 192.168.56.100
MAC: aa:bb:cc:dd:ee:ff
#
# arp -n
Address HWtype HWaddress Flags Mask Iface
192.168.56.1 ether 00:50:56:c0:00:08 C eth0
192.168.56.254 ether 00:50:56:f8:57:2f C eth0
192.168.56.100 ether aa:bb:cc:dd:ee:ff CM eth0
192.168.56.2 ether 00:50:56:f4:a3:a0 C eth03 . 指定本地网络接口名称与目标主机IP地址作为参数，删除对应的ARP条目
/* del_arp_entry_ioctl.c */
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <net/if_arp.h>
static void del_arp_entry(char *, char *);
int main(int argc, char *argv[])
{
if (argc != 3) {
fprintf(stderr,
"Usage: %s [local interface name] [dst ip addres]\n", argv[0]);
exit(EXIT_FAILURE);
}
char ifname[IFNAMSIZ] = {'\0'};
strncpy(ifname, argv[1], IFNAMSIZ-1);
char ipaddr[INET_ADDRSTRLEN] = {'\0'};
strncpy(ipaddr, argv[2], INET_ADDRSTRLEN);
del_arp_entry(ifname, ipaddr);
printf("Deleting an arp entry done.\n");
}
static void del_arp_entry(char *dev, char *ip)
{
int sfd, saved_errno, ret;
struct arpreq arp_req;
struct sockaddr_in *sin;
sfd = socket(AF_INET, SOCK_DGRAM, 0);
sin = (struct sockaddr_in *)&(arp_req.arp_pa);
memset(&arp_req, 0, sizeof(arp_req));
sin->sin_family = AF_INET;
strncpy(arp_req.arp_dev, dev, IFNAMSIZ-1);
inet_pton(AF_INET, ip, &(sin->sin_addr));
saved_errno = errno;
ret = ioctl(sfd, SIOCDARP, &arp_req);
if (ret < 0) {
fprintf(stderr, "Delete ARP entry failed : %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
errno = saved_errno;
}编译并运行
# gcc del_arp_entry_ioctl.c -g3 -DC=-5 -o del_arp_entry_ioctl
#
# ./del_arp_entry_ioctl eth0 192.168.56.100
Deleting an arp entry done.
#
# ./del_arp_entry_ioctl eth0 192.168.56.200
Delete ARP entry failed : No such device or address
#
# ./del_arp_entry_ioctl eth1 192.168.56.100
Delete ARP entry failed : No such device or address
#
# arp -n
Address HWtype HWaddress Flags Mask Iface
192.168.56.1 ether 00:50:56:c0:00:08 C eth0
192.168.56.254 ether 00:50:56:f8:57:2f C eth0
192.168.56.100 (incomplete) eth0
192.168.56.2 ether 00:50:56:f4:a3:a0 C eth0
#
# cat /proc/net/arp
IP address HW type Flags HW address Mask Device
192.168.56.1 0x1 0x2 00:50:56:c0:00:08 * eth0
192.168.56.254 0x1 0x2 00:50:56:f8:57:2f * eth0
192.168.56.100 0x1 0x0 aa:bb:cc:dd:ee:ff * eth0
192.168.56.2 0x1 0x2 00:50:56:f4:a3:a0 * eth0
#
# ./get_arp_entry_ioctl eth0 192.168.56.100
MAC: Not in the ARP cache.