Not able to receive UDP/IPv6 packets on secondary interface

Question

I have the following C code for UDP server which would bind to the ipv6 address of the secondary interface tap0.

context_t *
new_context(const struct sockaddr *listen_addr, size_t addr_size) {
  context_t *c = malloc( sizeof( context_t ) );
  time_t now;
  int reuse = 1;

  if (!listen_addr) {
    fprintf(stderr, "no listen address specified\n");
    return NULL;
  }

  srand( getpid() ^ time(&now) );

  if ( !c ) {
    perror("init: malloc:");
    return NULL;
  }

  memset(c, 0, sizeof( context_t ) );

  c->sockfd = socket(listen_addr->sa_family, SOCK_DGRAM, 0);
  if ( c->sockfd < 0 ) {
    perror("new_context: socket");
    goto onerror;
  }

  if ( setsockopt( c->sockfd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse) ) < 0 )
    perror("setsockopt SO_REUSEADDR");

  if ( bind (c->sockfd, listen_addr, addr_size) < 0 ) {
    perror("new_context: bind");
    goto onerror;
  }

  return c;

 onerror:
  if ( c->sockfd >= 0 )
    close ( c->sockfd );
  free( c );
  return NULL;
}



context_t *
get_context(const char *ipaddress, const char *port, unsigned int  scopeId) {
  int s;
  context_t* ctx;
  struct addrinfo hints;
  struct addrinfo *result, *rp;

  memset(&hints, 0, sizeof(struct addrinfo));
  hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
  hints.ai_socktype = SOCK_DGRAM; /* Coap uses UDP */
  hints.ai_flags = AI_PASSIVE | AI_NUMERICHOST | AI_NUMERICSERV | AI_ALL;

  s = getaddrinfo(ipaddress, port, &hints, &result);
  if ( s != 0 ) {
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
    return NULL;
  } 

  /* iterate through results until success */
  for (rp = result; rp != NULL; rp = rp->ai_next) {
    ctx = new_context(rp->ai_addr, rp->ai_addrlen);
    if (ctx) {
      if ( rp->ai_family == PF_INET6 ) {
         struct sockaddr_in6* pSadrIn6 = (struct sockaddr_in6*) rp->ai_addr;
         if ( pSadrIn6->sin6_scope_id == 0 ) {
            pSadrIn6->sin6_scope_id = scopeId;
         }  /* End IF the scope ID wasn't set. */
      }
      goto finish;
    }
  }

  fprintf(stderr, "no context available for interface '%s'\n", node);

 finish:
  freeaddrinfo(result);
  return ctx;
}

Device tap0 has following details:

tap0      Link encap:Ethernet  HWaddr ce:23:fc:81:7f:65  
          inet6 addr: fe80::cc23:fcff:fe81:7f65/64 Scope:Link
          inet6 addr: aaaa::1/64 Scope:Global

I run the above code with the following command:

./server -A aaaa::1

But it's not able to listen to the messages coming to the address aaaa::1 on tap0. I can see the packets on the wireshark dump on tap0 interface. Interestingly, the server ran from the above command(and code) can receive the messages through the localhost. So, if I execute the following command, the server receives the messages:

nc -6 -vvv -u aaaa::1 61616 < /tmp/send_to_node_raw 

The above command sending and reception is done through localhost. Is there any way I can programatically receive UDP/IPv6 messages on secondary interfaces?

Answer 1

The problem must be somewhere else. Using the code above I can successfully receive packets from another node using aaaa::1/64 and aaaa::2/64 as the local and remote addresses, respectively.

Try to bind to :: and see if it works that way. Also try to use netcat6 to bind to aaaa::1 and receive from another netcat6 instance.