>Hi,
> I have the name of the remote host in my local network. I will get
>the IP address of the remote host by using gethostbyname() function.
> I will get the name of the local machine using gethostname. and IP
>address by using gethostbyname.
Using gethostname may not provide what you expect. IP addresses
are assigned to interfaces, so a given host could possibly have
several different interfaces active, and each would have at
least one IP address, and likely at least one host name
associated with it. Which one you get from gethostname depends
on configuration, and may not be related to the IP address which
the remote host uses to address the local host on your local
network.
Hence, you are probably more interested in getting the IP
address of a specific interface, or at most of all interfaces of
a given type (i.e., in this case most likely eth0 or else all
ethernet interfaces).
Quote:> Now I want to check that the given IP address ( remote host ) is in
>my subnet or not. For that I need to get the Subnet Mask of the
>network. Is there any API to get the subnet mask of the network ?
You can use socket ioctl() calls. Below is a generic program which
lists a number of parameters for each interface. It does a lot more
than what you are specifically asking, but in the process demonstrates
how to select on a number of different criteria. For example, you
can use it to show only information about ethernet interfaces, or only
PPP, or whatever. You'll need to trim out the parts unnecessary for
you program.
/*
* display info about network interfaces
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <net/if_arp.h>
#include <arpa/inet.h>
#define inaddrr(x) (*(struct in_addr *) &ifr->x[sizeof sa.sin_port])
#define IFRSIZE ((int)(size * sizeof (struct ifreq)))
int main(void)
{
unsigned char *u;
int sockfd, size = 1;
struct ifreq *ifr;
struct ifconf ifc;
struct sockaddr_in sa;
if (0 > (sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP))) {
fprintf(stderr, "Cannot open socket.\n");
exit(EXIT_FAILURE);
}
ifc.ifc_len = IFRSIZE;
ifc.ifc_req = NULL;
do {
++size;
/* realloc buffer size until no overflow occurs */
if (NULL == (ifc.ifc_req = realloc(ifc.ifc_req, IFRSIZE))) {
fprintf(stderr, "Out of memory.\n");
exit(EXIT_FAILURE);
}
ifc.ifc_len = IFRSIZE;
if (ioctl(sockfd, SIOCGIFCONF, &ifc)) {
perror("ioctl SIOCFIFCONF");
exit(EXIT_FAILURE);
}
} while (IFRSIZE <= ifc.ifc_len);
ifr = ifc.ifc_req;
for (;(char *) ifr < (char *) ifc.ifc_req + ifc.ifc_len; ++ifr) {
if (ifr->ifr_addr.sa_data == (ifr+1)->ifr_addr.sa_data) {
continue; /* duplicate, skip it */
}
if (ioctl(sockfd, SIOCGIFFLAGS, ifr)) {
continue; /* failed to get flags, skip it */
}
printf("Interface: %s\n", ifr->ifr_name);
printf("IP Address: %s\n", inet_ntoa(inaddrr(ifr_addr.sa_data)));
/*
This won't work on HP-UX 10.20 as there's no SIOCGIFHWADDR ioctl. You'll
need to use DLPI or the NETSTAT ioctl on /dev/lan0, etc (and you'll need
to be root to use the NETSTAT ioctl. Also this is deprecated and doesn't
work on 11.00).
On Digital Unix you can use the SIOCRPHYSADDR ioctl according to an old
utility I have. Also on SGI I think you need to use a raw socket, e.g. s
= socket(PF_RAW, SOCK_RAW, RAWPROTO_SNOOP)
Dave
*/
if (0 == ioctl(sockfd, SIOCGIFHWADDR, ifr)) {
/* Select which hardware types to process.
*
* See list in system include file included from
* /usr/include/net/if_arp.h (For example, on
* Linux see file /usr/include/linux/if_arp.h to
* get the list.)
*/
switch (ifr->ifr_hwaddr.sa_family) {
default:
printf("\n");
continue;
case ARPHRD_NETROM: case ARPHRD_ETHER: case ARPHRD_PPP:
case ARPHRD_EETHER: case ARPHRD_IEEE802: break;
}
u = (unsigned char *) &ifr->ifr_addr.sa_data;
if (u[0] + u[1] + u[2] + u[3] + u[4] + u[5]) {
printf("HW Address: %2.2x.%2.2x.%2.2x.%2.2x.%2.2x.%2.2x\n",
u[0], u[1], u[2], u[3], u[4], u[5]);
}
}
if (0 == ioctl(sockfd, SIOCGIFNETMASK, ifr) &&
strcmp("255.255.255.255", inet_ntoa(inaddrr(ifr_addr.sa_data)))) {
printf("Netmask: %s\n", inet_ntoa(inaddrr(ifr_addr.sa_data)));
}
if (ifr->ifr_flags & IFF_BROADCAST) {
if (0 == ioctl(sockfd, SIOCGIFBRDADDR, ifr) &&
strcmp("0.0.0.0", inet_ntoa(inaddrr(ifr_addr.sa_data)))) {
printf("Broadcast: %s\n", inet_ntoa(inaddrr(ifr_addr.sa_data)));
}
}
if (0 == ioctl(sockfd, SIOCGIFMTU, ifr)) {
printf("MTU: %u\n", ifr->ifr_mtu);
}
if (0 == ioctl(sockfd, SIOCGIFMETRIC, ifr)) {
printf("Metric: %u\n", ifr->ifr_metric);
}
printf("\n");
}
close(sockfd);
return EXIT_SUCCESS;
Quote:}
--
Floyd L. Davidson <http://www.ptialaska.net/~floyd>
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