linux原始套接字(2)-icmp请求与接收

一.概述                                                   

上一篇arp请求使用的是链路层的原始套接字。icmp封装在ip数据报里面，所以icmp请求可以直接使用网络层的原始套接字，即socket()第一个参数是PF_INET。如下：

1 sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP);

icmp报文不同的类型有不同的格式，我们以icmp回显请求和会显应答报文格式(即ping程序使用的报文类型)为例：

类型为8表示请求，为0表示应答。校验和要自己计算，标识符一般为程序的进程ID号。序号自定义，一般从1开始。选项数据里面可以放时间戳，用作计算ping一次的花费时间！

icmp报文结构定义在netinet/ip_icmp.h

 1 struct icmp
 2 {
 3   u_int8_t  icmp_type;    /* type of message, see below */
 4   u_int8_t  icmp_code;    /* type sub code */
 5   u_int16_t icmp_cksum;    /* ones complement checksum of struct */
 6   union
 7   {
 8     u_char ih_pptr;        /* ICMP_PARAMPROB */
 9     struct in_addr ih_gwaddr;    /* gateway address */
10     struct ih_idseq        /* echo datagram */
11     {
12       u_int16_t icd_id;
13       u_int16_t icd_seq;
14     } ih_idseq;
15     u_int32_t ih_void;
16 
17     /* ICMP_UNREACH_NEEDFRAG -- Path MTU Discovery (RFC1191) */
18     struct ih_pmtu
19     {
20       u_int16_t ipm_void;
21       u_int16_t ipm_nextmtu;
22     } ih_pmtu;
23 
24     struct ih_rtradv
25     {
26       u_int8_t irt_num_addrs;
27       u_int8_t irt_wpa;
28       u_int16_t irt_lifetime;
29     } ih_rtradv;
30   } icmp_hun;
31 #define    icmp_pptr    icmp_hun.ih_pptr
32 #define    icmp_gwaddr    icmp_hun.ih_gwaddr
33 #define    icmp_id        icmp_hun.ih_idseq.icd_id
34 #define    icmp_seq    icmp_hun.ih_idseq.icd_seq
35 #define    icmp_void    icmp_hun.ih_void
36 #define    icmp_pmvoid    icmp_hun.ih_pmtu.ipm_void
37 #define    icmp_nextmtu    icmp_hun.ih_pmtu.ipm_nextmtu
38 #define    icmp_num_addrs    icmp_hun.ih_rtradv.irt_num_addrs
39 #define    icmp_wpa    icmp_hun.ih_rtradv.irt_wpa
40 #define    icmp_lifetime    icmp_hun.ih_rtradv.irt_lifetime
41   union
42   {
43     struct
44     {
45       u_int32_t its_otime;
46       u_int32_t its_rtime;
47       u_int32_t its_ttime;
48     } id_ts;
49     struct
50     {
51       struct ip idi_ip;
52       /* options and then 64 bits of data */
53     } id_ip;
54     struct icmp_ra_addr id_radv;
55     u_int32_t   id_mask;
56     u_int8_t    id_data[1];
57   } icmp_dun;
58 #define    icmp_otime    icmp_dun.id_ts.its_otime
59 #define    icmp_rtime    icmp_dun.id_ts.its_rtime
60 #define    icmp_ttime    icmp_dun.id_ts.its_ttime
61 #define    icmp_ip        icmp_dun.id_ip.idi_ip
62 #define    icmp_radv    icmp_dun.id_radv
63 #define    icmp_mask    icmp_dun.id_mask
64 #define    icmp_data    icmp_dun.id_data
65 };

二.icmp请求代码                                   

  1 /**
  2  * @file icmp_request.c
  3  */
  4 
  5 #include <stdio.h>
  6 #include <stdlib.h>
  7 #include <string.h>
  8 #include <unistd.h>
  9 #include <sys/socket.h>
 10 #include <arpa/inet.h>
 11 #include <netinet/in.h>
 12 #include <netinet/ip_icmp.h>
 13 #include <sys/time.h>
 14 
 15 /* icmp报文长度 */
 16 #define ICMP_PACKET_LEN sizeof(struct icmp)
 17 
 18 void err_exit(const char *err_msg)
 19 {
 20     perror(err_msg);
 21     exit(1);
 22 }
 23 
 24 /* 校验和 */
 25 unsigned short check_sum(unsigned short *addr, int len)
 26 {
 27     int nleft = len;
 28     int sum = 0;
 29     unsigned short *w = addr;
 30     unsigned short answer = 0;
 31 
 32     while(nleft > 1)
 33     {
 34         sum += *w++;
 35         nleft -= 2;
 36     }
 37     if(nleft == 1)
 38     {
 39         *(unsigned char *)(&answer) = *(unsigned char *)w;
 40         sum += answer;
 41     }
 42 
 43     sum = (sum >> 16) + (sum & 0xffff);
 44     sum += (sum >> 16);
 45     answer = ~sum;
 46 
 47     return answer;
 48 }
 49 
 50 /* 填充icmp报文 */
 51 struct icmp *fill_icmp_packet(int icmp_type, int icmp_sequ)
 52 {
 53     struct icmp *icmp_packet;
 54 
 55     icmp_packet = (struct icmp *)malloc(ICMP_PACKET_LEN);
 56     icmp_packet->icmp_type = icmp_type;
 57     icmp_packet->icmp_code = 0;
 58     icmp_packet->icmp_cksum = 0;
 59     icmp_packet->icmp_id = htons(getpid());
 60     icmp_packet->icmp_seq = htons(icmp_sequ);
 61     /* 发送时间 */
 62     gettimeofday((struct timeval *)icmp_packet->icmp_data, NULL);
 63     /* 校验和 */
 64     icmp_packet->icmp_cksum = check_sum((unsigned short *)icmp_packet, ICMP_PACKET_LEN);
 65 
 66     return icmp_packet;
 67 }
 68 
 69 /* 发送icmp请求 */
 70 void icmp_request(const char *dst_ip, int icmp_type, int icmp_sequ)
 71 {
 72     struct sockaddr_in dst_addr;
 73     struct icmp *icmp_packet;
 74     int sockfd, ret_len;
 75     char buf[ICMP_PACKET_LEN];
 76 
 77     /* 请求的地址 */
 78     bzero(&dst_addr, sizeof(struct sockaddr_in));
 79     dst_addr.sin_family = AF_INET;
 80     dst_addr.sin_addr.s_addr = inet_addr(dst_ip);
 81 
 82     if ((sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1)
 83         err_exit("sockfd()");
 84 
 85     /* icmp包 */
 86     icmp_packet = fill_icmp_packet(icmp_type, icmp_sequ);
 87     memcpy(buf, icmp_packet, ICMP_PACKET_LEN);
 88 
 89     /* 发送请求 */
 90     ret_len = sendto(sockfd, buf, ICMP_PACKET_LEN, 0, (struct sockaddr *)&dst_addr, sizeof(struct sockaddr_in));
 91     if (ret_len > 0)
 92         printf("sendto() ok!!!\n");
 93 
 94     close(sockfd);
 95 }
 96 
 97 int main(int argc, const char *argv[])
 98 {
 99     if (argc != 2)
100     {
101         printf("usage:%s dst_ip\n", argv[0]);
102         exit(1);
103     }
104 
105     /* 发送icmp请求 */
106     icmp_request(argv[1], 8, 1);
107 
108     return 0;
109 }

流程：命令行接收icmp请求的目标IP，106行发送请求，指定icmp类型是8，序列号是1。然后通过目标IP地址创建网络地址结构，接着创建ICMP类型的原始套接字，填充icmp报文，并把发送时间填到icmp的数据结构。

三.icmp接收代码                                   

 1 /**
 2  * @file icmp_recv.c
 3  */
 4 
 5 #include <stdio.h>
 6 #include <stdlib.h>
 7 #include <string.h>
 8 #include <unistd.h>
 9 #include <sys/time.h>
10 #include <sys/socket.h>
11 #include <arpa/inet.h>
12 #include <netinet/in.h>
13 #include <netinet/ip.h>
14 #include <netinet/ip_icmp.h>
15 
16 /* IP首部长度 */
17 #define IP_HEADER_LEN sizeof(struct ip)
18 /* icmp报文长度 */
19 #define ICMP_PACKET_LEN sizeof(struct icmp)
20 /* IP + ICMP长度 */
21 #define IP_ICMP_PACKET_LEN IP_HEADER_LEN + ICMP_PACKET_LEN
22 
23 void err_exit(const char *err_msg)
24 {
25     perror(err_msg);
26     exit(1);
27 }
28 
29 /* 计算发送时间与接收时间的毫秒差 */
30 float time_interval(struct timeval *recv_time, struct timeval *send_time)
31 {
32     float msec = 0;
33 
34     /* 如果接收的时间微妙小于发送的微妙 */
35     if (recv_time->tv_usec < send_time->tv_usec)
36     {
37         recv_time->tv_sec -= 1;
38         recv_time->tv_usec += 1000000;
39     }
40     msec = (recv_time->tv_sec - send_time->tv_sec) * 1000.0 + (recv_time->tv_usec - send_time->tv_usec) / 1000.0;
41 
42     return msec;
43 }
44 
45 int main(void)
46 {
47     struct ip *ip_header;
48     struct icmp *icmp_packet;
49     char buf[IP_ICMP_PACKET_LEN];
50     struct timeval *recv_timeval, *send_timeval;
51     int sockfd, ret_len;
52 
53     if ((sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1)
54         err_exit("sockfd()");
55 
56     recv_timeval = malloc(sizeof(struct timeval));
57     while (1)
58     {
59         ret_len = recv(sockfd, buf, IP_ICMP_PACKET_LEN, 0);
60         if (ret_len > 0)
61         {
62             /* 接收时间 */
63             gettimeofday(recv_timeval, NULL);
64             /* 取出ip首部 */
65             /* 取出icmp报文 */
66             ip_header = (struct ip *)buf;
67             icmp_packet = (struct icmp *)(buf + IP_HEADER_LEN);
68             /* 取出发送时间 */
69             send_timeval = (struct timeval *)icmp_packet->icmp_data;
70             printf("===============================\n");
71             printf("from ip:%s\n", inet_ntoa(ip_header->ip_src));
72             printf("icmp_type:%d\n", icmp_packet->icmp_type);
73             printf("icmp_code:%d\n", icmp_packet->icmp_code);
74             printf("time interval:%.3fms\n", time_interval(recv_timeval, send_timeval));
75         }
76     }
77 
78     free(recv_timeval);
79     close(sockfd);
80     return 0;
81 }

流程：创建ICMP类型的原始套接字后直接接收。首先获取接收时间，然后依次取出ip首部，icmp报文，再取出icmp的请求时间。从ip首部获取源ip地址，从icmp报文获取该报文的类型，代码号，通过发送时间和接收时间计算毫秒差！

四.实验                                                   

1.打开wireshark一起观察。以root运行icmp_recv，再运行icmp_request

可以看到icmp的类型是0，代码也是0。响应时间跟我们的程序差不多。

2.现在我们请求一个不可达的ip地址

主机不可达时，返回的icmp报文类型是3，代码是1。报文结构不同，取出的发送时间是不正常的，所以这里计算的时间间隔也不正常。wireshark里面的结果是，本机自动广播了一个arp请求，但没有机器回答本机。

部分icmp类型：