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 32enum { 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 ]