使用C ++将完整的以太网数据包发送到特定的IP

Question

I am trying to send a full packet to specific IP address. The point is that I already have full packet binary and I don't want it to be encapsulated into any additional packet headers. Here is my logic:

std::string destination_ip = "127.0.0.1";
uint16_t destination_port = 8080;
int socket_fd;

struct sockaddr_in socket_attrs;

if ((socket_fd = socket(AF_INET, SOCK_PACKET, htons(ETH_P_ALL))) < 0)
{
    printf("Socket creation error\n");
    return false;
}

memset(&socket_attrs, '0', sizeof(socket_attrs));

socket_attrs.sin_family = AF_INET;
socket_attrs.sin_port = htons(destination_port);

if(inet_pton(AF_INET, destination_ip.c_str(), &socket_attrs.sin_addr)<=0)
{
    printf("Invalid IP address/ IP address not supported\n");
    return false;
}

if (connect(socket_fd, (struct sockaddr *)&socket_attrs, sizeof(socket_attrs)) < 0)
{
    printf("Connection Failed\n");
    return false;
}

if((write(socket_fd , <PACKET_DATA> , <PACKET_SIZE>)) < 0){
    std::cout << "Error sending packets to the network" << std::endl;
    exit(1);
}

Output:

Connection Failed

Could anyone help me achieve my goal?

Answer 1

Use libpcap , pcap_inject() in particular.

You cannot use socket() , using IPPROTO_RAW either, because L2(eth) and L3(ip) will be forged by the IP stack of the OS in this case too.

You need to inject the packet directly into the network card. If you want it delivered to an IP different from the original one, you have to "edit" the packet contents.

Example pasted from here: http://www.microhowto.info/howto/send_an_arbitrary_ethernet_frame_using_libpcap.html

char pcap_errbuf[PCAP_ERRBUF_SIZE];
pcap_errbuf[0]='\0';

pcap_t* pcap=pcap_open_live(if_name,65536,0,0,pcap_errbuf);
if (pcap_errbuf[0]!='\0') {
    fprintf(stderr,"%s",pcap_errbuf);
}

if (!pcap) {
    exit(1);
}

if (pcap_inject(pcap, <PACKET_DATA> , <PACKET_SIZE> )==-1) {
    pcap_perror(pcap,0);
    pcap_close(pcap);
    exit(1);
}

pcap_close(pcap)

If you don't want to edit the IP destination, the packet will be able to reach the other end of the wire only if you haven't switches/routers between the two peers.

As an alternative the OP suggesting to use a tunnel. It actually works (I tested it with tcpreplay ) - you can use a GRE tunnel, which actually can transport ethernet traffic too.

On the two peers you can establish a gretap tunnel. I used these commands:

on host A (its IP address is 192.168.1.211):

ip link add gretap1 type gretap local 192.168.1.211 remote 192.168.1.64
ip link set gretap1 up

on host B (its IP address is 192.168.1.64):

ip link add gretap1 type gretap local 192.168.1.64 remote 192.168.1.211
ip link set gretap1 up

At this point it's possible to use the L2 GRE tunnel and let it transport ETH traffic using the gretap1 interfaces. On one peer I injected the traffic into the tunnel with the command:

tcpreplay -i gretap1 test.pcap

and on the other peer verified the traffic was transmitted capturing it on the gretap1 interface using wireshark or tcpdump.

Unfortunately there is a problem with this setup: the MTU of the tunnel is smaller than the MTU of the network, so it's not guaranteed that you can replay all the packets.