今天尝试用winpcap提供的pcap_sendpacket函数成功发送一个udp数据包到目的地址。下面就来回顾一下过程。

首先用pcap_findalldevs得到网络接口，比如在我的机器上得到这样的结果：

1: /Device/NPF_GenericDialupAdapter
2: /Device/NPF_{06864041-9387-44DC-AF44-37779B0F2E9E}

现在我们及应用"/Device/NPF_{06864041-9387-44DC-AF44-37779B0F2E9E}“对应的接口发送数据。

由于发送数据必须自己构建以太网数据头， IP数据包头 和 UDP数据包头， 数据结构大概是这个样子的。

" 以太网数据头 |  IP数据头 | UDP数据包头 | 数据"

以太网数据头结构如下，

struct   ether_header{
 u_char   ether_dhost[ETHER_ADDR_LEN];
 u_char   ether_shost[ETHER_ADDR_LEN];
 u_short   ether_type;  //如果上一层为IP协议。则ether_type的值就是0x0800
};

以太网地址填充什么数据， 我不是很清楚， 你可以填上实际的地址， 我这里全部填1.

IP数据头

struct ip_header  //小端模式__LITTLE_ENDIAN
{
 unsigned   char  ihl:4;    //ip   header   length   
 unsigned   char  version:4;   //version  
 u_char    tos;    //type   of   service  
 u_short    tot_len;   //total   length  
 u_short    id;     //identification  
 u_short    frag_off;   //fragment   offset  
 u_char    ttl;    //time   to   live  
 u_char    protocol;   //protocol   type  
 u_short    check;    //check   sum  
 u_int    saddr;    //source   address  
 u_int    daddr;    //destination   address  
};

tot_len为 整个IP数据包长度 （IP数据头 | UDP数据包头 | 数据）

ihl 为IP数据头的总长度 除以4.  （4字节对齐）

check 为在数据填好后， check为0 时的校验和， 是对于IP数据头。

u_int16_t in_cksum (u_int16_t * addr, int len) { int nleft = len; u_int32_t sum = 0; u_int16_t *w = addr; u_int16_t answer = 0; while (nleft > 1) { sum += *w++; nleft -= 2; } if (nleft == 1) { * (unsigned char *) (&answer) = * (unsigned char *) w; sum += answer; } sum = (sum >> 16) + (sum & 0xffff); sum += (sum >> 16); answer = ~sum; return (answer); }

protocol 为IPPROTO_UDP。

UDP数据包头

struct udphdr
{
  u_int16_t source;        
  u_int16_t dest;   
  u_int16_t len;           
  u_int16_t checkl;        
};

len 为UDP数据包长度，

checkl  校验和（IP为首部 | UDP数据包头 | 数据），这个比较特殊一点，要加一个伪首部

struct Psd_Header {
 ULONG sourceip; //源IP地址
 ULONG destip; //目的IP地址
 BYTE mbz; //置空(0)
 BYTE ptcl; //协议类型
 USHORT plen; //TCP/UDP数据包的长度(即从TCP/UDP报头算起到数据包结束的长度 单位:字节)
};

plen 和UDP长度是一样的。

当把这些都填充好了， 就可以用pcap_sendpacket发送出去了

#define HAVE_REMOTE #include <pcap.h> #pragma comment(lib, "wpcap.lib") #include <stdio.h> #pragma comment(lib, "Ws2_32.lib") //typedef void(* pcap_handler)(u_char *user, const struct pcap_pkthdr *pkt_header, const u_char *pkt_data) void my_pcap_handler(u_char *user, const struct pcap_pkthdr *pkt_header, const u_char *pkt_data); #define ETHER_ADDR_LEN 6 //from linux's ethernet.h #define ETHERTYPE_PUP 0x0200 #define ETHERTYPE_SPRITE 0x0500 #define ETHERTYPE_IP 0x0800 #define ETHERTYPE_ARP 0x0806 #define ETHERTYPE_REVARP 0x8035 #define ETHERTYPE_AT 0x809B #define ETHERTYPE_AARP 0x80F3 #define ETHERTYPE_VLAN 0x8100 #define ETHERTYPE_IPX 0x8137 #define ETHERTYPE_IPV6 0x86dd #define ETHERTYPE_LOOPBACK 0x9000 struct ether_header{ u_char ether_dhost[ETHER_ADDR_LEN]; u_char ether_shost[ETHER_ADDR_LEN]; u_short ether_type; //如果上一层为IP协议。则ether_type的值就是0x0800 }; char* prase_ether_host(u_char ether_host[ETHER_ADDR_LEN], char* buffer); struct ip_header //小端模式__LITTLE_ENDIAN { unsigned char ihl:4; //ip header length unsigned char version:4; //version u_char tos; //type of service u_short tot_len; //total length u_short id; //identification u_short frag_off; //fragment offset u_char ttl; //time to live u_char protocol; //protocol type u_short check; //check sum u_int saddr; //source address u_int daddr; //destination address }; struct tcphdr //小端模式__LITTLE_ENDIAN { u_int16_t source; u_int16_t dest; u_int32_t seq; u_int32_t ack_seq; u_int16_t res1:4; u_int16_t doff:4; u_int16_t fin:1; u_int16_t syn:1; u_int16_t rst:1; u_int16_t psh:1; u_int16_t ack:1; u_int16_t urg:1; u_int16_t res2:2; u_int16_t window; u_int16_t check; u_int16_t urg_ptr; }; struct udphdr { u_int16_t source; u_int16_t dest; u_int16_t len; u_int16_t checkl; }; char* uint_to_addr(u_int addr); u_int16_t in_cksum (u_int16_t * addr, int len) { int nleft = len; u_int32_t sum = 0; u_int16_t *w = addr; u_int16_t answer = 0; while (nleft > 1) { sum += *w++; nleft -= 2; } if (nleft == 1) { * (unsigned char *) (&answer) = * (unsigned char *) w; sum += answer; } sum = (sum >> 16) + (sum & 0xffff); sum += (sum >> 16); answer = ~sum; return (answer); } struct Psd_Header { ULONG sourceip; //源IP地址 ULONG destip; //目的IP地址 BYTE mbz; //置空(0) BYTE ptcl; //协议类型 USHORT plen; //TCP/UDP数据包的长度(即从TCP/UDP报头算起到数据包结束的长度 单位:字节) }; har* device = "//Device//NPF_{06864041-9387-44DC-AF44-37779B0F2E9E}"; pcap_t* adhandle = NULL; char errbuf[PCAP_ERRBUF_SIZE] = { 0 }; void main() { if((adhandle = pcap_open(device, 0x10000, PCAP_OPENFLAG_PROMISCUOUS, 1000, NULL, errbuf)) == NULL) { printf("[pcap_open error] : %s/n", errbuf); return; } char buffer[64] = { 0 }; ether_header* pether_header = (ether_header*)buffer; ip_header* pip_herder = (ip_header*)(buffer + sizeof(ether_header)); udphdr* pudp_herder = (udphdr*)(buffer + sizeof(ether_header) + sizeof(ip_header)); pether_header->ether_dhost[0] = 1; //0x0 * 16 + 0x0;; pether_header->ether_dhost[1] = 1; //0x2 * 16 + 0x1; pether_header->ether_dhost[2] = 1; //0x2 * 16 + 0x7; pether_header->ether_dhost[3] = 1; //0x2 * 16 + 0x3; pether_header->ether_dhost[4] = 1; //0x7 * 16 + 0x2; pether_header->ether_dhost[5] = 1; //0xf * 16 + 0xe; pether_header->ether_shost[0] = 1; //0x0 * 16 + 0x0;; pether_header->ether_shost[1] = 1; //0x1 * 16 + 0xF; pether_header->ether_shost[2] = 1; //0xD * 16 + 0x0; pether_header->ether_shost[3] = 1; //0x1 * 16 + 0x6; pether_header->ether_shost[4] = 1; //0x6 * 16 + 0x3; pether_header->ether_shost[5] = 1; //0x7 * 16 + 0x1; pether_header->ether_type = htons(ETHERTYPE_IP); //构建IP数据头 if((sizeof(ip_header) % 4) != 0) { printf("[IP Header error]/n"); return; } pip_herder->ihl = sizeof(ip_header) / 4; pip_herder->version = 4; pip_herder->tos = 0; pip_herder->tot_len = htons(sizeof(buffer) - sizeof(ether_header)); pip_herder->id = htons(0x1000); pip_herder->frag_off = htons(0); pip_herder->ttl = 0x80; pip_herder->protocol = IPPROTO_UDP; pip_herder->check = 0; pip_herder->saddr = inet_addr("192.168.18.*"); pip_herder->daddr = inet_addr("122.*.*.*"); pip_herder->check = in_cksum((u_int16_t*)pip_herder, sizeof(ip_header)); //构建UDP数据头; pudp_herder->dest = htons(7865); pudp_herder->source = htons(2834); pudp_herder->len = htons(sizeof(buffer) - sizeof(ether_header) - sizeof(ip_header)); pudp_herder->checkl = 0; //构造伪UDP首部 //pudp_herder->checkl = in_cksum((u_int16_t*)pudp_herder, 24); char buffer2[64] = { 0 }; Psd_Header* psd = (Psd_Header*)buffer2; psd->sourceip = inet_addr("192.168.18.*"); psd->destip = inet_addr("122.*.*.*"); psd->ptcl = IPPROTO_UDP; psd->plen = htons(sizeof(buffer) - sizeof(ether_header) - sizeof(ip_header)); psd->mbz = 0; memcpy(buffer2 + sizeof(Psd_Header), (void*)pudp_herder, sizeof(buffer) - sizeof(ether_header) - sizeof(ip_header)); pudp_herder->checkl = in_cksum((u_int16_t *)buffer2, sizeof(buffer) - sizeof(ether_header) - sizeof(ip_header) + sizeof(Psd_Header)); if(pcap_sendpacket(adhandle, (const u_char*)buffer, 64) == -1) { printf("[pcap_sendpacket error]/n"); return; } }