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setting IP address from C

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setting IP address from C

Postby alainB » Thu Jan 15, 2004 10:14 am

Could you please tell me how to set an IP address with an ioctl() call.
I don't know how to fill the sockaddr structure.

I tried some UNIX examples but they don't work, they just clear my
actual IP address.

Thanks,
Alain.
alainB
Active Member
 
Posts: 34
Joined: Tue Jan 27, 2004 11:43 am

Re: setting IP address from C

Postby Janusz Ruszel » Thu Jan 15, 2004 3:54 pm

I hope it helps!

struct ifreq ifr;
int local_IP_socket;
// descriptor (an fd) for the socket use to set up IP data
char ip_addr[IP_ADDR_BUFLEN]="10.2.12.89"; // device's new IP address
char subnet_mask[IP_ADDR_BUFLEN]="255.255.255.0"; //
subnet mask
bool iface_enabled;
// 'true' if we are to set a new IP address


local_IP_socket = socket(AF_INET, SOCK_DGRAM, 0);
if (local_IP_socket == DIRECTIVE_FAILURE)
{
printf("Cannot create local address socket");
exit(0);
}

::memset(&ifr, 0, sizeof(ifr));
::strcpy(ifr.ifr_name, Interface);

/*
| For those of you that don't speak the gibberish that passes for QNX (or
BSD, probably)
| ioctl() requests, here's a part of the rosetta stone: SIOCDIFADDR means
"delete the current
| IF (which, for some unknown reason QNX uses to mean "IP" as in Internet
Protocol) address".
| (I don't know how you're supposed to know that it takes a pointer to an
ifreq structure as
| the optional third parameter, or what's supposed to go in there....)
*/
if (ioctl(local_IP_socket, SIOCDIFADDR, &ifr) == DIRECTIVE_FAILURE)
{
/*
| Attempt to delete the old IP address failed. It may have failed
because it was previously
| deleted in the session. We would know this because errno would be set
to EADDRNOTAVAIL.
| So if errno is set thus, we continue on knowing that the IP address
has been cleared.
|
| Of course, NONE of this is documented in the QNX "documentation"; this
has been determined
| by observation!
*/
if (errno != EADDRNOTAVAIL)
{
printf("Cannot delete old IP address");
exit(0);
}
else
{
printf("IP addr already deleted" );
}
}
printf("Old IP address deleted");

/*
| If the interface is enabled, we (re)define the IP address of this device,
and define the
| subnet mask (in that order).
*/

struct sockaddr_in sa; // used to define the new IP address

::memset(&sa, 0, sizeof(struct sockaddr_in));
sa.sin_family = AF_INET;
sa.sin_len = sizeof(sa);
sa.sin_port = 0;
inet_aton(ip_addr, &sa.sin_addr);
::memcpy(&(ifr.ifr_addr), &sa, sizeof(sa));

/*
| Here's a little bit more of the rosetta stone: SIOCSIFADDR means "set the
IF (which, we've
| established above, means IP) address". Again, it magically takes a pointer
to an ifreq
| structure of unknown contents.
*/
if (ioctl(local_IP_socket, SIOCSIFADDR, &ifr) == DIRECTIVE_FAILURE)
{
printf("Cannot define new IP address for this device");
}

/*
| Local IP address set, now set the subnet mask. Again, more rosetta stone:
SIOCSIFNETMASK
| means "set the subnet mask for the device". Note that the socket address
structure is
| mostly set up; all we really have to do is change the address portion of
it.
*/
inet_aton(subnet_mask, &sa.sin_addr);
::memcpy(&(ifr.ifr_addr), &sa, sizeof(sa));

if (ioctl(local_IP_socket, SIOCSIFNETMASK, &ifr) == DIRECTIVE_FAILURE)
{
printf("Cannot define subnet mask for this device");
exit(0);
}

/*
| All we needed the socket for is to set the IP (I will *NOT* call it an IF)
address, so
| we do not need to keep it open anymore.
*/
close(local_IP_socket);

"Alain Bonnefoy" <alain.bonnefoy@icbt.com> wrote in message
news:40066809.8030406@icbt.com...
Could you please tell me how to set an IP address with an ioctl() call.
I don't know how to fill the sockaddr structure.

I tried some UNIX examples but they don't work, they just clear my
actual IP address.

Thanks,
Alain.
Janusz Ruszel
 


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