ICMP-pingwithbaremin

/*
 ________________________________________________________   //4Byte
|____type_____|____code_____|_____________chksum_________|  //4Byte
|_________data______________|_____________data___________|
|                                                        |
|                                                        |




*/
 1 #include<stdio.h>
 2 #include<stdlib.h>
 3 #include<arpa/inet.h>
 4 #include<sys/socket.h>
 5 #include<fcntl.h>
 6 #include<unistd.h>
 7 #include<netdb.h>
 8 
 9 int main(){
10      int s = socket(PF_INET,SOCK_RAW,1);//建立//原始套接字能夠讀寫內核沒有處理的IP數據包，而流式套接字只能讀取TCP協議的數據，數據報套接字只能讀取UDP協議的數據
11   // printf("--%d--\n",s);
12      if (s <= 0){
13       perror("socket erro");
14       exit(0);
15      }
16      typedef struct{  //ICMP請求頭部
17          uint8_t type;
18          uint8_t code;
19          uint16_t chksum;
20          uint32_t data;
21      }icmp_hdr_t;
22 
23      icmp_hdr_t  pckt;
24 
25      pckt.type=8;       //1Byte
26      pckt.code=0;       //1Byte
27      pckt.chksum=0xfff7;//2Byte
28      pckt.data=0;       //4Byte
29 
30      struct sockaddr_in addr;//目的地的信息
31  
32      addr.sin_family=AF_INET;
33      addr.sin_port=0;
34      addr.sin_addr.s_addr=inet_addr("8.8.8.8");//Ping的目的地址
35    //addr.sin_zero[]="";
36     int actionSendResult=sendto(s,&pckt,sizeof(pckt),0,(struct sockaddr *)&addr,sizeof(addr));
37 
38     if(actionSendResult<=0){
39       perror("ping erro");
40       exit(0);
41     }
42     unsigned int resAddressSize;
43     unsigned char res[100]="";
44     struct sockaddr resAddress;
45   //printf("%u\n",resAddressSize);

46     int ressponse=recvfrom(s,res,sizeof(res),0,&resAddress,&resAddressSize);
47     if(ressponse>0){
48        printf("message is %d bytes long, and looks like this :\n",ressponse);
49        for(int i=0;i<ressponse;i++) printf("%02hhx ",res[i]);
50        printf("\n");
51      //exit(0);
52   
53     }else{
54        perror("ressponse error");
55        exit(0);
56     }
57     printf("resAddressSize:%u\n",resAddressSize);
58     struct sockaddr_in * temp;
59     temp=(struct sockaddr_in *)&resAddress;
60     printf("protocol:%d\n",temp->sin_family);
61     printf("port:%d\n",temp->sin_port);
62     return 0;
63 }

1.從下圖得

   發送：ICMP-->IP-->Ethernet

2.接收：Ethenet-->IP-->ICMP

  recvfrom()直接從Ethenet接收內容

 

3.recvfrom()接收任意ICMP數據

4.WireShark沒有ICMP協議的數據包，但程序有返回信息，說明recvfrom並未操做在ICMP之上，而是接收數據鏈路層處理完的數據（原始套接字能夠讀寫內核沒有處理的IP數據包，而流式套接字只能讀取TCP協議的數據，數據報套接字只能讀取UDP協議的數據）

目的地址不可達，recvfrom()爲何會接收到「消息」，哪裏來的消息？什麼協議？

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