[ECOS] Change IP during run-time (netmask change ...)

sebastien Couret sebastien.couret@elios-informatique.fr
Wed Apr 14 16:18:00 GMT 2004

On Wednesday 14 April 2004 16:26, Richard Rauch wrote:
> Hi,
> we were also interested on this information. we implemented as described
> and it works,
> but with this solution it is not possible to change the network mask, too.
> How we have to do this?
> Best Regards
> Richard

It's almost the same for changing netmask, but you got to use a 
SIOCSIFNETMASK call to ioctl instead of SIOCSIFADDR

Here is an example procedure I wrote for doing such thing
Parameter interface is a string like "eth0" and and adresse is a sub-netmask 
such "".
It returns 0 if all is right.

Sorry, comments are in French but I hope it helps.

int IP_SetMask(const char* interface,const char * adresse)
 int test_sock=0;
 struct sockaddr_in* addr=NULL;
 struct sockaddr * addrp=NULL;
 struct ifreq ifr;

 memset( &ifr, 0, sizeof( struct ifreq ) );
 addrp = (struct sockaddr *)&(ifr.ifr_addr);
 addr= (struct sockaddr_in *)addrp;
 memset(addr, 0, sizeof( struct sockaddr) );
 addr->sin_len=sizeof(struct sockaddr_in);

 test_sock = socket( PF_INET, SOCK_DGRAM, 0 );
 if( test_sock == -1 )
  diag_printf("Impossible d'obtenir la socket :%s",strerror(errno));
  return (-1);

 strncpy( ifr.ifr_name,interface,IFNAMSIZ);
 if( ioctl( test_sock, SIOCSIFNETMASK, &ifr ) == -1 )
  diag_printf("Impossible de fixer le masque de sous-réseau de '%s' à '%s' 
car '%s'",interface,adresse,strerror(errno));
  return (-1);
 diag_printf("Masque de sous-réseau de '%s' fixé à '%s'",interface,adresse);

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