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POWireshark doesn't detect any packet sent. sendto return 0
 

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    <p>I have been trying to send packets using raw socket in following code.This code I found somewhere in the internet. I created my own ipheader and udp header. The whole data packet is sent using sendto() function on raw socket. sendto() returns 0. Which means a packet of 0 length is sent out of it and hence even wireshark doesnt detect any packet. Where is my mistake?</p> <pre><code>// Must be run by root lol! Just datagram, no payload/data #include &lt;unistd.h&gt; #include &lt;stdio.h&gt; #include &lt;string.h&gt; #include &lt;cstdlib&gt; #include &lt;arpa/inet.h&gt; #include &lt;sys/socket.h&gt; #include &lt;netinet/ip.h&gt; #include &lt;netinet/udp.h&gt; // The packet length #define PCKT_LEN 35 // Can create separate header file (.h) for all headers' structure // The IP header's structure struct ipheader { unsigned char iph_ihl:4, iph_ver:4; unsigned char iph_tos; unsigned short int iph_len; unsigned short int iph_ident; unsigned char iph_flag; unsigned short int iph_offset; unsigned char iph_ttl; unsigned char iph_protocol; unsigned short int iph_chksum; unsigned int iph_sourceip; unsigned int iph_destip; }; // UDP header's structure struct udpheader { unsigned short int udph_srcport; unsigned short int udph_destport; unsigned short int udph_len; unsigned short int udph_chksum; }; // total udp header length: 8 bytes (=64 bits) // Function for checksum calculation. From the RFC, // the checksum algorithm is: // "The checksum field is the 16 bit one's complement of the one's // complement sum of all 16 bit words in the header. For purposes of // computing the checksum, the value of the checksum field is zero." unsigned short csum(unsigned short *buf, int nwords) { // unsigned long sum; for(sum=0; nwords&gt;0; nwords--) sum += *buf++; sum = (sum &gt;&gt; 16) + (sum &amp;0xffff); sum += (sum &gt;&gt; 16); return (unsigned short)(~sum); } // Source IP, source port, target IP, target port from the command line arguments int main(int argc, char *argv[]) { int sd; // No data/payload just datagram char buffer[PCKT_LEN]; // Our own headers' structures struct ipheader *ip = (struct ipheader *) buffer; struct udpheader *udp = (struct udpheader *) (buffer + sizeof(struct ipheader)); // Source and destination addresses: IP and port struct sockaddr_in sin, din; int one = 1; const int *val = &amp;one; memset(buffer, 0, PCKT_LEN); if(argc != 5) { printf("- Invalid parameters!!!\n"); printf("- Usage %s &lt;source hostname/IP&gt; &lt;source port&gt; &lt;target hostname/IP&gt; &lt;target port&gt;\n", argv[0]); exit(-1); } // Create a raw socket with UDP protocol sd = socket(PF_INET, SOCK_RAW, IPPROTO_UDP); if(sd &lt; 0) { perror("socket() error"); // If something wrong just exit exit(-1); } else printf("socket() - Using SOCK_RAW socket and UDP protocol is OK.\n"); // The source is redundant, may be used later if needed // The address family sin.sin_family = AF_INET; din.sin_family = AF_INET; // Port numbers sin.sin_port = htons(atoi(argv[2])); din.sin_port = htons(atoi(argv[4])); // IP addresses sin.sin_addr.s_addr = inet_addr(argv[1]); din.sin_addr.s_addr = inet_addr(argv[3]); // Fabricate the IP header or we can use the // standard header structures but assign our own values. ip-&gt;iph_ihl = 5; ip-&gt;iph_ver = 4; ip-&gt;iph_tos = 16; // Low delay ip-&gt;iph_len = sizeof(struct ipheader) + sizeof(struct udpheader); ip-&gt;iph_ident = htons(54321); ip-&gt;iph_ttl = 64; // hops ip-&gt;iph_protocol = 17; // UDP // Source IP address, can use spoofed address here!!! ip-&gt;iph_sourceip = inet_addr(argv[1]); // The destination IP address ip-&gt;iph_destip = inet_addr(argv[3]); // Fabricate the UDP header. Source port number, redundant udp-&gt;udph_srcport = htons(atoi(argv[2])); // Destination port number udp-&gt;udph_destport = htons(atoi(argv[4])); udp-&gt;udph_len = htons(sizeof(struct udpheader)); // Calculate the checksum for integrity ip-&gt;iph_chksum = csum((unsigned short *)buffer, sizeof(struct ipheader) + sizeof(struct udpheader)); // Inform the kernel do not fill up the packet structure. we will build our own... if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) &lt; 0) { perror("setsockopt() error"); exit(-1); } else printf("setsockopt() is OK.\n"); // Send loop, send for every 2 second for 100 count printf("Trying...\n"); printf("Using raw socket and UDP protocol\n"); printf("Using Source IP: %s port: %u, Target IP: %s port: %u.\n", argv[1], atoi(argv[2]), argv[3], atoi(argv[4])); int count; int i; for(count = 1; count &lt;=20; count++) { if(i = sendto(sd, buffer, PCKT_LEN, 0, (struct sockaddr *)&amp;sin, sizeof(sin)) &lt; 0) // Verify { perror("sendto() error"); exit(-1); } else { printf("Count #%u - sendto() is OK. Data Length#%d\n", count,i); sleep(2); } } close(sd); return 0; } </code></pre>
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    1. USShashi Bhushan
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    1. COThis is too hard to read.
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    2. COI edited it to make it "better", but I think some of the original spaces were lost. Perhaps Shashi could edit and use the {} to mark the code rather than ` `.
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      1. USMats Petersson
    3. COI think, however, that 0 packet len means that "nothing was sent", so wireshark won't see anything, because you never sent a packet. As to why that is, I'm not sure.
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