sendto returns with Invalid Argument on UDP Raw Socket ipv6 in Linux due to sin6_port value?

Question

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/ip6.h>
#include <netinet/udp.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>

struct ip6_hdr;
struct udphdr;

int main(){
  int clientSocket, portNum, nBytes;
  char buffer[1024];
  struct sockaddr_in serverAddr;
  struct sockaddr_in6 serverAddr6;
  socklen_t addr_size;
  struct hostent *hp;
  struct msghdr m;
  struct in_addr **addr_list;
  /*Create UDP socket*/
 clientSocket = socket(PF_INET6, SOCK_RAW, IPPROTO_RAW);

  /*Configure settings in address struct*/
  hp = gethostbyname2("2001:0db8:0:f101::2", PF_INET6);
  memset((char *)&serverAddr6, 0, sizeof(serverAddr6));
  memcpy((char *)&serverAddr6.sin6_addr, hp->h_addr, hp->h_length);
  serverAddr6.sin6_family = hp->h_addrtype;
  // serverAddr6.sin6_port   = htons(7891);
  serverAddr6.sin6_port   = 0;//htons(IPPROTO_RAW);

  /*Initialize size variable to be used later on*/
  const size_t IPV6_HEADER_LEN = 40;
  const size_t UDP_HEADER_LEN  = 8;
  addr_size = sizeof serverAddr6;
  size_t data_len = sizeof(serverAddr6) - IPV6_HEADER_LEN;

  /*Populate ip header*/
  struct ip6_hdr *iphdr = (struct ip6_hdr *)buffer;
  iphdr->ip6_flow = htonl ((6 << 28) | (0 << 20) | 0); // IPv6 version (4 bits), Traffic class (8 bits), Flow label (20 bits)
  iphdr->ip6_plen = data_len;

  iphdr->ip6_nxt = IPPROTO_UDP;
  iphdr->ip6_hops = 64;

  //supposing src_addr and dst_addr pointers are never NULL
  memcpy(&iphdr->ip6_src, (const in6_addr*)&serverAddr6.sin6_addr, sizeof(in6_addr));
  memcpy(&iphdr->ip6_dst, (const in6_addr*)&serverAddr6.sin6_addr, sizeof(in6_addr));

  /*Populate UDP header*/
  udphdr * udp_header = reinterpret_cast<udphdr *>(buffer + IPV6_HEADER_LEN);
  udp_header->source = htons(0);
  udp_header->dest   = htons(7891);

  int len = sizeof(serverAddr6);
  uint32_t data_length = (len - (IPV6_HEADER_LEN + UDP_HEADER_LEN));
  udp_header->len      = htons(data_length + sizeof(udphdr));
  udp_header->check    = htons(0);

  for (int i=0; i<10; ++i)
  {
      sprintf(buffer, "%d", i);
      nBytes = strlen(buffer) + 1;

      /*Send message to server*/
      if(sendto(clientSocket,buffer,nBytes,0,(struct sockaddr *)&serverAddr6,addr_size) == -1 )
      {
          printf("sendto(): %s\n", strerror(errno));
          exit(0);
      }

      /*Receive message from server*/
      // nBytes = recvfrom(clientSocket,buffer,1024,0,NULL, NULL);
      // nBytes = recvmsg(clientSocket,&m,0);
    if((nBytes = recvmsg(clientSocket,&m, 0)) == -1)
    {
      printf("recvmsg(): %s\n", strerror(errno));
      // exit(0);
    }
      printf("Received from server: %s\n",buffer);
  }

  return 0;
}

I am pretty new to socket programming. I have the following code. It returns sendto(): Invalid argument Upon investigation, I have identified that the line containing: serverAddr6.sin6_port = htons(7891); *commented out in the code snippet With the help of Google, I have found a work around solution in http://osdir.com/ml/linux.ipv6.usagi.users/2003-03/msg00004.html :

From the kernel source code, it seems that when you use raw ipv6 socket, you have to set

dest.sin6_port = htons(IPPROTO_RAW);

and in http://osdir.com/ml/linux.ipv6.usagi.users/2003-03/msg00005.html :

dest.sin6_port=0;

On the other hand, I cannot go with this proposed solution as I have to specify the port to be something else other than 0.

Any suggestions or explanations?

Answer 1

I am using Python 3, and also encountering OSError: [Errno 22] Invalid argument when sending IPv6 packages. However, when I set the port number of the parameter for sendto to 0 , the packets are sent successfully and the port specified in the packet generated by the script ( buffer in your program) is still used.

You should use different port numbers for generating the packet and calling sendto . Generate with the desired port number and call with port number 0 .

The following is my code

s = socket.socket(AF_INET6, SOCK_RAW, IPPROTO_RAW)
s.setsockopt(IPPROTO_IPV6, IP_HDRINCL, 1)
s.sendto(GenerateIPv6Packet('::1', 53, '::1', 53), ('::1', 0))
    # generate the packet with port 53 and call sendto with port 0

Sorry for answering in a different programming language.