trouble with sockets and sendto()

[lughbh]

Hi,
I have a short function which is trying to send an
icmp message out a raw ipv6 socket.

when I run the following code I get "wrote -1"...
i.e. sendto() is returning an error. Can someone
please tell me what I'm doing wrong?
-----
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <netinet/icmp6.h>

int main() {
int sockfd,len,out;
struct sockaddr_in6 myDst;
struct icmp6_hdr *hdr;
char sendbuff[1500]=&quot;abcdefghijklmnop&quot;;

out=0;

sockfd=socket(AF_INET6,SOCK_RAW,IPPROTO_ICMPV6);
if( !inet_pton(AF_INET6,'fed0:10:100::1&quot;,&myDst) )
printf(&quot;bad address\n&quot;

hdr=(struct icmp6_hdr *)sendbuff;
hdr->icmp6_type=ND_ROUTER_ADVERT; //don't care about type... just want to send!
hdr->icmp6_code=0;
hdr->icmp6_cksum=0;
hdr->icmp6_seq=htons(6); //dummy val
hdr->icmp6_id=htons(8);//dummy val

out=sendto(sockfd, (char *) sendbuff, 8, 0, (struct sockaddr *) &myDst, sizeof(myDst));
printf(&quot;wrote %d\n&quot;,out);

return 1;
}
-----
thank-you so much!!

 

[danielhozac]

Try printing the error message too, that would probably help you to diagnose the problem further.

//Daniel

 

[lughbh]

I get
22: Invalid argument

I was suspecting whether I was passing a pointer
wrong... maybe you can point it out?

sendto (int s, const void *msg, size_t len, int flags,
const struct sockaddr *to, socklen_t tolen)

... myDst is not a pointer, so I have to pass it's
location to satisfy sendto(). maybe my flag value
shouldn't be 0, but there are examples in the book
where it is 0.

 

[JasonDeckard]

sendto() sets errno to EINVAL when it doesn't like one of the specified lengths. The man page on my HP/UX box indicates the minimum/maximum message length varies by protocol.

Try increasing the message you're sending from 8 bytes to 60 bytes.