Receive raw ethernet packets in c

Question

I'm wirting two programms for sending and receiving raw ethernet packets. I can send packets and I can receive, but I have two problems with my receiver.

First: All packtes are duplicated, it means all in comming packets are shown twice. It's only with a connection on 2 virtual networkinterfaces.(e.g. src tap0 mac 00:00:8F:00:00:02 -> dest tap1 mac 00:00:8F:00:00:03)

Second: All packets in the network are received form my programm, but it should receive packets from the specific interface.

Informations: I work on Ubuntu 12.04.01 LTS in a VirtualBox

Here my receiver code:

/*read while first char not * */
while(frame.data[0] != '*'){
    length_in_byte = recvfrom(sock_desc, buffer, ETH_FRAME_LEN,0,NULL,NULL);
    if(length_in_byte == -1){
        error handling
    }

    frame.dest_mac[0] = buffer[0];
    frame.dest_mac[1] = buffer[1];
    frame.dest_mac[2] = buffer[2];
    frame.dest_mac[3] = buffer[3];
    frame.dest_mac[4] = buffer[4];
    frame.dest_mac[5] = buffer[5];

    frame.src_mac[0] = buffer[6];
    frame.src_mac[1] = buffer[7];
    frame.src_mac[2] = buffer[8];
    frame.src_mac[3] = buffer[9];
    frame.src_mac[4] = buffer[10];
    frame.src_mac[5] = buffer[11];

    for(dataRun = 14; dataRun < length_in_byte; dataRun++){
        frame.data[dataRun-14] = buffer[dataRun];
    }
    /*print struct*/
    printf("\n");
    printf("src: %02x:%02x:%02x:%02x:%02x:%02x\t->\tdest: %02x:%02x:%02x:%02x:%02x:%02x\n",frame.src_mac[0],frame.src_mac[1],frame.src_mac[2],frame.src_mac[3],frame.src_mac[4],frame.src_mac[5],frame.dest_mac[0],frame.dest_mac[1],frame.dest_mac[2],frame.dest_mac[3],frame.dest_mac[4],frame.dest_mac[5]);
    printf("Data: %s\n", frame.data);

}

Terminal Output: send data = test

src: 00:00:8f:00:00:03  ->  dest: 00:00:8f:00:00:02
Data: test

src: 00:00:8f:00:00:03  ->  dest: 00:00:8f:00:00:02
Data: test

send data = a

src: 00:00:8f:00:00:03  ->  dest: 00:00:8f:00:00:02
Data: a

src: 00:00:8f:00:00:03  ->  dest: 00:00:8f:00:00:02
Data: a

src: 00:00:8f:00:00:03  ->  dest: 33:33:00:00:00:fb
Data: `

src: 00:00:8f:00:00:03  ->  dest: 33:33:00:00:00:fb
Data: `

score 0 · Answer 1 · answered Jul 17 '13 at 10:14

0

for the first problem :

the while loop " while(frame.data[0] != '*') " cause the duplication of packet. maybe you have to check also if the packet is fragmented

answered Jul 17 '13 at 10:14

stack_A

713
4
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How that? The packet is an ethernet packet and has up to 1500 bytes. As I am sending only a few bytes there is nothing being fragmented? The duplicated data is obviously caused by the blocking recvfrom, that receives two times in a row the same data or something... any ideas? – Patzde Jul 17 '13 at 12:27
I use the recvfrom function but I have no duplicated data !! ==> could you please give us all the code to run the same program – stack_A Jul 17 '13 at 14:34

score 0 · Accepted Answer · answered Jul 19 '13 at 07:58

I have found a solution for my problem with the duplication, it's not the source code for my programms.

The problem was the connection from the virtual ethernet devices, I've change the connection methode form tap0 to tap1.

I use yet the vde_switch. For Problem two I must find a filter.

Thanks a lot for your help

Receive raw ethernet packets in c

2 Answers2