On Oct 12, 2012 9:36 PM, "Pietro Paolini" [off-list ref]
wrote:

Hello,

I am struggling with the byte order question on a x86_32 arch, I am doing

some modifications on a program which actually works fine on a MIPS arch.

I do a reading from a RAW socket in this way:

        /* Configure socket */
        if ((fd = socket(AF_INET, SOCK_RAW, IPPROTO_IGMP)) < 0) {
                perror("Error on socket creation, exit");
                exit(1);
        }
          ....
        if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, (void *)&va,

sizeof(va))) {

                perror("Error on setsockopt, exit");
                exit(1);
        }
        va = 0;
        ....
        ....
        struct msghdr mhdr;
        struct __in_pktinfo *pktinfo = NULL;
        ...
        ...
        nrd = recvmsg(env->mrouter_fd, &mhdr, 0);
        ...
        ip = (struct iphdr *)iov.iov_base;

When I print the saddr (or daddr) of the received ip packet it is printed

as host byte order instead of what I am expecting, the network byte order.
I can just use the htonl() family functions for solve the problem but I
would like understand if it is the normal behavior or if there is an issues
on my code, or if the device driver of my NIC can influence the question.

I think you should use ntoh*() functions when accessing data rx'ed from the
n/w. Network byte order is big endian and your host is little endian, so
you'll have convert it to the right order before accessing. You should use
hton*() functions when tx'ing data. CMIIW.

HTH,
-mandeep

Many thanks,
Pietro.


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