Question

我在c ++中模拟tcp协议的3次握手，以及我的代码运行时的wireshark。我的代码在ip和tcp层创建头文件，打包它们，然后将它发送到一个http服务器，并将tcp头的SYN标志设置为1。

我可以在wireshark上看到带有ip和tcp头的完整数据报。似乎没有错误。我的进程使用与已发送数据包标头中包含的地址和端口相同的套接字绑定套接字。

Wireshark显示已成功发送的数据包但服务器上没有任何收入数据包确认我的SYN。我做错了什么？

我在Ubuntu 10.10,2.6.35-23。

代码很乱，对不起。它仅用于测试。

main.cpp中：

    char host[100],buf[1000],*data=NULL,source_ip[20]; //buf is the complete packet
sockaddr_in dest;
hostent *server;
IPV4_HDR *v4hdr=NULL;
TCP_HDR *tcphdr=NULL;
memset(&buf, 0, sizeof(buf));

cout << "Creating RAW socket..." << endl;
int s;
if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_TCP)) == -1) {
    cout << "Error creating socket: " << errno << endl;
    return 1;
}

cout << "Setting the socket in RAW mode..." << endl;
int optval = 1;
if ((setsockopt(s, IPPROTO_IP, IP_HDRINCL, &optval, sizeof(optval))) == -1) {
    cout << "Failed to set socket in RAW mode..." << endl;
    return 1;
}
cout << "Successful.\n";

cout << "nResolving Hostname..." << endl;
if((server=gethostbyname("www.site.com"))==0)
{
    cout << "Unable to resolve." << endl;
    return 1;
}
dest.sin_family = AF_INET;
dest.sin_port = htons(50000); 
memcpy(&dest.sin_addr.s_addr,server->h_addr,server->h_length);
cout << "Resolved." << endl;

v4hdr = (IPV4_HDR *)buf; //lets point to the ip header portion
v4hdr->ip_version=4;
v4hdr->ip_header_len=5;
v4hdr->ip_tos = 16;
v4hdr->ip_total_length = htons ( sizeof(IPV4_HDR) + sizeof(TCP_HDR) );
v4hdr->ip_id = htons(2);
v4hdr->ip_frag_offset = 0;
v4hdr->ip_frag_offset1 = 0;
v4hdr->ip_reserved_zero = 0;
v4hdr->ip_dont_fragment = 1;
v4hdr->ip_more_fragment = 0;
v4hdr->ip_ttl = 64;
v4hdr->ip_protocol = IPPROTO_TCP;
v4hdr->ip_srcaddr = inet_addr("192.168.0.103");
v4hdr->ip_destaddr = inet_addr(inet_ntoa(dest.sin_addr));
v4hdr->ip_checksum = 0;

tcphdr = (TCP_HDR *)&buf[sizeof(IPV4_HDR)]; //get the pointer to the tcp header in the packet

tcphdr->source_port = htons(52000);
tcphdr->dest_port = htons(80);
tcphdr->window = htons(5840);
tcphdr->acknowledge = 0;
tcphdr->data_offset = 8;
tcphdr->urg=0;
tcphdr->ack=0;
tcphdr->psh=0;
tcphdr->rst=0;
tcphdr->syn=1;
tcphdr->fin=0;
tcphdr->options1=htonl(0x020405b4);
tcphdr->options2=htonl(0x04020103);
tcphdr->options3=htonl(0x03060000);

cout << sizeof(*tcphdr) << endl;

//tcphdr->ns=0;

tcphdr->checksum = csum((unsigned short *) buf, (sizeof(ip_hdr) + sizeof(tcp_header)));;
int bytes = 0;
if((bytes = sendto(s , buf , sizeof(IPV4_HDR)+sizeof(TCP_HDR), 0,
(sockaddr *)&dest, sizeof(dest)))==-1)
{
    cout << "Error sending packet: " << errno << endl;
    return 1;
}
cout << bytes << " bytes sent!" << endl;
close(s);

//这是在tcp.h ...

typedef struct ip_hdr
{
unsigned char ip_header_len:4; // 4-bit header length (in 32-bit words)

                               // normally=5 (Means 20 Bytes may be 24 also)

unsigned char ip_version :4;   // 4-bit IPv4 version

unsigned char ip_tos;          // IP type of service

unsigned short ip_total_length; // Total length

unsigned short ip_id;          // Unique identifier


unsigned char ip_frag_offset :5; // Fragment offset field


unsigned char ip_more_fragment :1;
unsigned char ip_dont_fragment :1;
unsigned char ip_reserved_zero :1;

unsigned char ip_frag_offset1; //fragment offset


unsigned char ip_ttl;          // Time to live

unsigned char ip_protocol;     // Protocol(TCP,UDP etc)

unsigned short ip_checksum;    // IP checksum

unsigned int ip_srcaddr;       // Source address

unsigned int ip_destaddr;      // Source address

} IPV4_HDR;


// TCP header

typedef struct tcp_header
{
unsigned short source_port;   // source port

unsigned short dest_port;     // destination port

unsigned int sequence;        // sequence number - 32 bits

unsigned int acknowledge;     // acknowledgement number - 32 bits

unsigned char reserved_part1:4; //according to rfc
unsigned char data_offset:4;    /*The number of 32-bit words
                                  in the TCP header.
                                  This indicates where the data begins.
                                  The length of the TCP header
                                  is always a multiple
                                  of 32 bits.*/

unsigned char fin :1; //Finish Flag

unsigned char syn :1; //Synchronise Flag

unsigned char rst :1; //Reset Flag

unsigned char psh :1; //Push Flag

unsigned char ack :1; //Acknowledgement Flag

unsigned char urg :1; //Urgent Flag

unsigned char reserved_part2:2;

unsigned short window :16; // window




//unsigned char ns :1;          //Nonce Sum Flag Added in RFC 3540.

//unsigned char ecn :1; //ECN-Echo Flag

//unsigned char cwr :1; //Congestion Window Reduced Flag


////////////////////////////////


unsigned short checksum; // checksum

unsigned short urgent_pointer; // urgent pointer

unsigned int options1;
unsigned int options2;
unsigned int options3;

} TCP_HDR;

Answer 1

你还没有到目前为止，但是你需要防火墙使用本地端口，这样内核就不会用RST回复SYN / ACK。

如何正确地重现与原始套接字的TCP协议3次握手？

1 个答案: