Linu网络接口操作之ioctl-2_ARP条目
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 -nAddress HWtype HWaddress Flags Mask Iface192.168.56.254 ether 00:50:56:f8:57:2f C eth0192.168.56.2 ether 00:50:56:f4:a3:a0 C eth0192.168.56.1 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 # include # include # include # include # include # include # include # include # include 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 # include # include # include # include # include # include # include # include # include # include 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 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:ffAdding an arp entry done.# # ./get_arp_entry_ioctl eth0 192.168.56.100MAC: aa:bb:cc:dd:ee:ff# # arp -nAddress HWtype HWaddress Flags Mask Iface192.168.56.1 ether 00:50:56:c0:00:08 C eth0192.168.56.254 ether 00:50:56:f8:57:2f C eth0192.168.56.100 ether aa:bb:cc:dd:ee:ff CM eth0192.168.56.2 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 # include # include # include # include # include # include # include # include # include 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 192.168.56.100Deleting an arp entry done.# # ./del_arp_entry_ioctl eth0 192.168.56.200Delete ARP entry failed : No such device or address# # ./del_arp_entry_ioctl eth1 192.168.56.100Delete ARP entry failed : No such device or address# # arp -nAddress HWtype HWaddress Flags Mask Iface192.168.56.1 ether 00:50:56:c0:00:08 C eth0192.168.56.254 ether 00:50:56:f8:57:2f C eth0192.168.56.100 (incomplete) eth0192.168.56.2 ether 00:50:56:f4:a3:a0 C eth0# # cat /proc/net/arp IP address HW type Flags HW address Mask Device192.168.56.1 0x1 0x2 00:50:56:c0:00:08 * eth0192.168.56.254 0x1 0x2 00:50:56:f8:57:2f * eth0192.168.56.100 0x1 0x0 aa:bb:cc:dd:ee:ff * eth0192.168.56.2 0x1 0x2 00:50:56:f4:a3:a0 * eth0# # ./get_arp_entry_ioctl eth0 192.168.56.100MAC: Not in the ARP cache.关键字：c, linux
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