#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
	in_addr_t ip;
	in_addr_t i;
	in_addr_t netmask;
	in_addr_t network;
	in_addr_t broadcast;

	int netbits;         /* how many network bits */
	int hostbits;        /* how many host bits */
	struct hostent *p;
	char buffer[INET_ADDRSTRLEN];

	if (argc != 3) {
		fprintf(stderr, "%s: requires 2 arguments: IP netbits\n",
			argv[0]);
		return 1;
	}

	if (inet_pton(AF_INET, argv[1], &ip) != 1) {
		fprintf(stderr, "%s: first argument %s must be a dotted IPv4 address\n",
			argv[0], argv[1]);
		return 2;
	}
	
	i = ntohl(ip);

	netbits = strtol(argv[2], NULL, 10);   /* string to long */
	if (netbits <= 0 || netbits > 30) {
		fprintf(stderr, "%s: second argument %s must be number of network bits\n",
			argv[0], argv[2]);
		return 3;
	}

	hostbits = 32 - netbits;

	/* The netmask is netbits 1's, followed by hostbits 0's. */
	netmask = -1 << hostbits;

	/* The network address is the IP address, with all the host bits turned
	off. */
	network = i & netmask;

	/* The broadcast address is the IP address, with all the host bits
	turned on. */
	broadcast = i | ~netmask;

	for (i = network + 1; i < broadcast; ++i) {
		ip = htonl(i);
		p = gethostbyaddr((char *)&ip, sizeof ip, AF_INET);
		if (p != NULL) {
			if (inet_ntop(AF_INET, &ip, buffer, sizeof buffer) !=
				buffer) {
				fprintf(stderr, "%s: inet_ntop failed\n",
					argv[0]);
				return 4;
			}
			printf("%s %s\n", buffer, p->h_name);
		}
	}

	return EXIT_SUCCESS;
}