Messages in this thread |  | | Date | Mon, 19 May 2003 14:18:04 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: Impossible to turn BROADCAST mode off on ethernet device? |
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On Mon, 19 May 2003, Denis Zaitsev wrote:
> Kernel 2.4.20. I do: > > ifconfig eth0 -broadcast > > And BROADCAST isn't turned off... The ethernet modules are: eepro100, > tulip, 3c59x. So, what does it mean? > > Thanks in advance.
Your `ifconfig` might not allow broadcast to be turned off as long a eth0 is `up`. So I just made a little program to get the flags, and reset the flags. This shows that your observation is, indeed, correct.
If you mess around with this, I think you will find that you can't set broadcast OFF as long at the IFF_UP flag is set. This may be the required behavior because an interface without broadcast capability will not work on ethernet because ARP requires it.
#include <stdio.h> #include <unistd.h> #include <errno.h> #include <netinet/in.h> #include <sys/socket.h> #include <sys/ioctl.h> #include <string.h> #include <net/if.h>
int main() { struct ifreq ifr; int s, status; if((s = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP)) == -1) { fprintf(stderr, "socket() failed (%s)\n", strerror(errno)); return s; } memset(&ifr, 0x00, sizeof(ifr)); ifr.ifr_netmask.sa_family = AF_INET; strcpy(ifr.ifr_name, "eth0"); status = ioctl(s, SIOCGIFFLAGS, &ifr); ifr.ifr_flags &= ~IFF_BROADCAST; status = ioctl(s, SIOCGIFFLAGS, &ifr);
(void)close(s); return status; }
Cheers, Dick Johnson Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips). Why is the government concerned about the lunatic fringe? Think about it.
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