[C] 程式範例-切割 subnet
為了學校作業寫的程式，用途是可將一大 IP 網段切割為數個小 subnet 輸出 問題敘述：試設計一程式，Input 為 IP與subnet的大小，Output為所有的 subnets 與 netmask。 編譯環境： 於UNIX, Linux, BSD, OS 上編譯：
gcc cidr.c -o cidr -Wall -lm
>> 執行格式說明：
$ ./cidr [IP address] [number of hosts per subnet] [ IP address ] 為IPv4位址 [ number of hosts per subnet ] 為每個子網域中的主機數目 範例：./cidr 192.168.0.0 8
流程說明 >> 取得INPUT資料： 1. 取得IP與每個subnet的host數目。 2. 檢查IP的格式是否正確。 3. 將十進位IP轉為二進位格式。 4. 檢查該IP屬於哪一種 class (A/B/C)。 5. 根據該IP的class取得預設之netmask。 6. 根據使用者輸入的 host 數目來求切割後subnet的netmask。 7. 計算該網段可切割為幾個subnet。 8. 輸出所有的subnet與netmask。 >> 輸出的資料儲存於”output.txt”。 執行結果： 說明：
1.$ ./cidr 192.168.1.0 8 >> 代表192.168.1.0此網段要切成每個subnet有8個hosts。 2.IP: 192.168.0.0 3.IP (bin): 11000000 10101000 00000000 00000000 >> 轉成二進位的IP。 4.Class: C >> 代表該IP屬於Class C。 5.Default netmaek: 255.255.255.0 >> class C預設 netmask 為 255.255.255.0。 6.Default netmask (bin): 11111111 11111111 11111111 00000000 >> 轉成二進位。 7.[Input] Host number/subnet: 5: >> 輸入每個subnet的hosts數目。 8.[FixTo] Host number/subnet: 8 >> 將 5 修正為最接近的hosts合法數目 8。 9.Host id: 3 >> host id 的 bit 數。 10.Subnet netmaek: 255.255.255.248 >> 計算出的每個subnet netmask。 11.Subnet netmask (bin): 11111111 11111111 11111111 11111000 >> 轉成二進 12.Subnet number: 32 >> 總共可以切割成 32 個 subnet。
/* Date: May, 2006
*
* Input:
* IP and the size of subnet
* Output:
* All subnets and the netmask
*
* Ref.
* [1] TCP/IP Protocol suite 2nd, chap 4 and chap5
* [2] http://www.study-area.org/network/network_ip_addr.htm
*
* Aaron Liao
*/
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
#define DEBUG 1
#define IP_ADDR_CLEN 16
#define IP_ADDR_BLEN 32
enum
{ TRUE = 0, FALSE };
/* class A 0
* class B 10
* class C 110
* Class D 1110
* Class E 1111
*/
enum ip_type
{ classA = 0, classB, classC, classD, classE };
int chk_class (char *bip);
int out_class (unsigned char class);
int get_orig_mask (unsigned int class, char *mask, char *bmask);
int get_new_mask (unsigned int host_bit, char *mask, char *bmask);
int no_buf (void);
int chk_ip (char *ip);
int get_host_num (unsigned long long *host, char *num,
unsigned int class, unsigned int *host_num);
int get_subnet_num (unsigned int class, unsigned int host_id,
unsigned int *sub);
int get_IP (char *ip, char *arg, char *bip);
int dec2bin (unsigned char *ip, unsigned char *bip);
int bin2dec (unsigned char *bip, unsigned char *ip);
int out_bin (char *str);
int out_subnet (char *bip, char *mask, unsigned int subnet_num,
unsigned int host_num, unsigned int host_id);
int usage (void);
int
chk_class (char *bip)
{
if (!bip[0])
return classA;
if (!bip[1])
return classB;
if (!bip[2])
return classC;
if (!bip[3])
return classD;
return classE;
}
int
out_class (unsigned char class)
{
printf ("\tClass: ");
switch (class)
{
case classA:
printf ("A\r\n");
break;
case classB:
printf ("B\r\n");
break;
case classC:
printf ("C\r\n");
break;
case classD:
printf ("D\r\n");
break;
case classE:
printf ("E\r\n");
break;
default:
/* should never */
printf ("?\r\n");
break;
}
return 0;
}
int
get_orig_mask (unsigned int class, char *mask, char *bmask)
{
switch (class)
{
case classA:
strcpy (mask, "255.0.0.0");
break;
case classB:
strcpy (mask, "255.255.0.0");
break;
case classC:
strcpy (mask, "255.255.255.0");
break;
default:
break;
}
printf ("\tDefault netmaek: %s\r\n", mask);
dec2bin (mask, bmask);
printf ("\tDefault netmask (bin): ");
out_bin (bmask);
return 0;
}
int
get_new_mask (unsigned int host_bit, char *mask, char *bmask)
{
unsigned int count, i;
for (count = 0; count < IP_ADDR_BLEN; count++)
bmask[count] = 1;
for (count = (IP_ADDR_BLEN - 1), i = host_bit; i > 0; i--, count--)
bmask[count] = 0;
bin2dec (bmask, mask);
printf ("\tSubnet netmaek: %s\r\n", mask);
printf ("\tSubnet netmask (bin): ");
out_bin (bmask);
return 0;
}
int
no_buf (void)
{
setbuf (stdout, 0);
return 0;
}
int
chk_ip (char *ip)
{
unsigned int count, i, state, error, count_num;
char *ptr = NULL, tmp[IP_ADDR_CLEN];
/* check there are three '.' */
for (i = 0, count = 0; i < IP_ADDR_CLEN; i++)
{
if (ip[i] == '.')
count++;
}
if (count != 3)
{
printf ("\t--> Error: [IP][.][%d] Incorrect IP format.\n\n", count);
return FALSE;
}
/* Check [0-9] and '.' */
for (i = 0; i < IP_ADDR_CLEN; i++)
{
if (ip[i] == '.' || (ip[i] >= '0' && ip[i] <= '9'))
continue;
if (ip[i] == '\0') /* End of string */
break;
printf ("\t--> Error: [IP] only [0-9] and '.'\r\n");
return FALSE;
}
strcpy (tmp, ip);
ptr = strtok (tmp, ".");
while (ptr != NULL)
{
if (atoi (ptr) > 255)
{
printf ("\t--> Error: [IP][%d] Incorrect IP format.\n\n",
atoi (ptr));
return FALSE;
}
ptr = strtok (NULL, ".");
}
/* check the order of number and '.'
* Format: number.number.number.number
*/
for (i = 0, error = 0, state = 0, count = 0, count_num = 0; i <
strlen (ip); i++)
{
switch (state)
{
case 0: /* '.' at the head */
if (ip[i] == '.')
error = 5;
else
{
state = 1;
count_num++;
}
break;
case 1: /* mid-number */
if (ip[i] == '.')
{
state = 2;
count++;
count_num = 0;
}
else
{
count_num++;
}
/* number is limited to three digits */
if (count_num > 3)
error = 1;
break;
case 2: /* . */
if (ip[i] == '.' || count > 3 || count_num > 3)
error = 2;
state = 1;
count_num++;
break;
default:
error = 4;
break;
}
if (error)
{
printf ("\t--> Error: [IP][Regular][%d] ", error);
printf ("There are some errors.\r\n");
return FALSE;
}
}
if (ip[i - 1] == '.')
{
printf ("\t--> Error: [IP][.] Can't end with '.'\r\n");
return FALSE;
}
return TRUE;
}
/*
* ip[]: "210.125.0.0"
* bip[]: 11010010011111010000000000000000
*/
int
dec2bin (unsigned char *ip, unsigned char *bip)
{
char *ptr = NULL;
unsigned char dec_ip[4] = { 0, 0, 0, 0 };
int count, j;
ptr = strtok (ip, ".");
for (count = 0; count < 4; count++)
{
if (ptr != NULL)
{
dec_ip[count] = atoi (ptr);
ptr = strtok (NULL, ".");
}
else
{
/* Error */
return FALSE;
}
}
/* dec-to-binary */
for (j = 3; j > (-1); j--)
{
for (count = 7; count > (-1); count--)
{
bip[8 * (j + 1) - count - 1] = ((dec_ip[j] & (1 <<(count))) > 0 ? 1 : 0);
}
}
return TRUE;
}
int
bin2dec (unsigned char *bip, unsigned char *ip)
{
int i, j;
unsigned int dec_ip[4] = { 0, 0, 0, 0 };
/* Support unsigned only */
for (i = 0, j = 0; i < IP_ADDR_BLEN; i++)
{
unsigned char _offset = i % 8;
if (_offset == 0 && i)
{
j++;
}
dec_ip[j] += (bip[i] <<(7 - _offset));
}
sprintf (ip, "%d.%d.%d.%d", dec_ip[0], dec_ip[1], dec_ip[2], dec_ip[3]);
return 0;
}
/* Input: the number of hosts per subnet
* The number of host(s) must be the power of 2.
* 2^0, 2^1, ... , 2^32
*/
int
chk_host_num (unsigned long long num)
{
unsigned int error, count;
/* Must be even */
if (num % 2)
return FALSE;
/* check if the power of 2 */
for (count = 0, error = 1; count < 32; count++)
{
if (num == (1 << count))
error = 0;
}
if (error)
return FALSE;
return 0;
}
int
get_host_num (unsigned long long *host, char *num,
unsigned int class, unsigned int *host_id)
{
unsigned int count;
const unsigned int max_len = 32;
unsigned long long max_hosts;
switch (class)
{
case classA:
max_hosts = pow (2, 24); /* powl */
break;
case classB:
max_hosts = pow (2, 16);
break;
case classC:
max_hosts = pow (2, 8);
break;
default:
return FALSE;
break;
}
for (count = 0; count < max_len && num[count] != '\0'; count++)
{
if (num[count] < '0' || num[count] > '9')
{
printf ("\t--> Error: [Host_num] limited to be [0-9]\r\n");
return FALSE;
}
}
(*host) = atoll (num);
if ((*host) < 2)
{
printf ("\t--> Error: [Host_num][%llu] is too small.\r\n", (*host));
return FALSE;
}
if ((*host) > pow (2, 32))
{
printf ("\t--> Error: [Host_num][%llu] is too large.\r\n", (*host));
return FALSE;
}
if ((*host) > max_hosts)
{
printf ("\t--> Error: [Host_num][Max: %llu] %llu is too large.\r\n",max_hosts, (*host));
return FALSE;
}
printf ("\t[Input] Host number/subnet: %llu\r\n", (*host));
for (count = 0; count < 32; count++)
{
if ((*host) <= pow (2, count))
{
(*host) = pow (2, count);
(*host_id) = count;
break;
}
}
printf ("\t[FixTo] Host number/subnet: %llu\r\n", (*host));
printf ("\tHost id: %d\r\n", (*host_id));
return 0;
}
int
get_IP (char *ip, char *arg, char *bip)
{
if (strlen (arg) > IP_ADDR_CLEN)
{
printf ("\t--> Error: [IP] %s incorrect format.\r\n", arg);
return FALSE;
}
if (strlen (arg) > IP_ADDR_CLEN)
strncpy (ip, arg, IP_ADDR_CLEN);
else
strncpy (ip, arg, strlen (arg));
if (chk_ip (ip))
return FALSE;
printf ("\tIP: %s\r\n", ip);
dec2bin (ip, bip);
printf ("\tIP (bin): ");
out_bin (bip);
return 0;
}
int
get_subnet_num (unsigned int class, unsigned int host_id, unsigned int *sub)
{
unsigned int tmp;
switch (class)
{
case classA:
tmp = (24 - host_id);
break;
case classB:
tmp = (16 - host_id);
break;
case classC:
tmp = (8 - host_id);
break;
default:
return FALSE;
break;
}
(*sub) = pow (2, tmp);
printf ("\tSubnet number: %d\r\n", (*sub));
return 0;
}
int
out_bin (char *str)
{
unsigned int count;
for (count = 0; count < IP_ADDR_BLEN; count++)
{
printf ("%d", str[count]);
if (count > 0 && !((count + 1) % 8))
printf (" ");
}
printf ("\r\n");
return 0;
}
int
out_subnet (char *bip, char *mask, unsigned int subnet_num,
unsigned int host_num, unsigned int host_id)
{
unsigned char ip[IP_ADDR_CLEN];
unsigned int i, j, k;
FILE *fp = NULL;
if ((fp = fopen ("output.txt", "w")) == NULL)
printf ("Can't open output.txt\r\n");
if (fp)
{
fprintf (fp, "Output: \r\n");
fprintf (fp, "netmask: [ %s ]\r\n", mask);
}
printf ("Output: \r\n");
printf ("netmask: [ %s ]\r\n", mask);
for (i = 0; i < subnet_num; i++)
{
bin2dec (bip, ip);
if (fp)
fprintf (fp, "Subnet %d: [ %s - ", i + 1, ip);
printf ("Subnet %d: [ %s - ", i + 1, ip);
for (j = 0; j < host_num - 1; j++)
{
/* binary increment */
for (k = (IP_ADDR_BLEN - 1); k > 0; k--)
{
bip[k] = (!bip[k]);
if (bip[k] == 1)
break;
}
}
bin2dec (bip, ip);
if (fp)
fprintf (fp, "%s ]\r\n", ip);
printf ("%s ]\r\n", ip);
/* add 1 */
for (k = (IP_ADDR_BLEN - 1); k > 0; k--)
{
bip[k] = (!bip[k]);
if (bip[k] == 1)
break;
}
}
if (fp)
fclose (fp);
return 0;
}
int
usage (void)
{
printf ("Usage: cidr [IP address] [number of hosts per subnet]\r\n");
printf ("\t ex. cidr 192.168.0.0 8\r\n");
return 0;
}
int
main (int argc, char *argv[])
{
unsigned char ip[IP_ADDR_CLEN], bip[IP_ADDR_BLEN], mask[IP_ADDR_CLEN], bmask[IP_ADDR_BLEN];
/* The number of hosts should be even, and the power of two,
* But I allow the user to use any number of hosts between
* 2^0 and 2^32. Then I calculate the approach value. ex.
* They want 5 hosts per subnet, and I find 8 hosts per subnet.
*/
unsigned long long host_num;
unsigned int host_bit, ip_class, subnet_num;
/* clean the output.txt */
fclose (fopen ("output.txt", "w"));
memset (ip, '\0', IP_ADDR_CLEN);
no_buf (); /* Don't buffer the standard output */
if (argc < 3 || argv[1] == NULL || argv[2] == NULL)
{
usage ();
return FALSE;
}
if (get_IP (ip, argv[1], bip))
return FALSE;
/* Get class of IP and normal netmask */
ip_class = chk_class (bip);
out_class (ip_class);
if (ip_class == classD || ip_class == classE)
return FALSE;
get_orig_mask (ip_class, mask, bmask);
/* Get the number of hosts */
if (get_host_num (&host_num, argv[2], ip_class, &host_bit))
return FALSE;
/* calculate the new netmask of subnet */
get_new_mask (host_bit, mask, bmask);
get_subnet_num (ip_class, host_bit, &subnet_num);
out_subnet (bip, mask, subnet_num, host_num, host_bit);
return 0;
}
執行結果範例：
./cidr 192.168.0.0 87 IP: 192.168.0.0 IP (bin): 11000000 10101000 00000000 00000000 Class: C Default netmaek: 255.255.255.0 Default netmask (bin): 11111111 11111111 11111111 00000000 [Input] Host number/subnet: 87 [FixTo] Host number/subnet: 128 Host id: 7 Subnet netmaek: 255.255.255.128 Subnet netmask (bin): 11111111 11111111 11111111 10000000 Subnet number: 2 Output: netmask: [ 255.255.255.128 ] Subnet 1: [ 192.168.0.0 - 192.168.0.127 ] Subnet 2: [ 192.168.0.128 - 192.168.0.255 ]
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