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1 office 1 /*
2 * Utility used to calculate the 6rd subnet.
3 *
4 * Copyright 2012, Stéphan Kochen <stephan@kochen.nl>
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version 2
9 * of the License, or (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
19 */
20  
21 #include <stdio.h>
22 #include <stdlib.h>
23 #include <string.h>
24 #include <sys/errno.h>
25 #include <arpa/inet.h>
26 #include <netinet/in.h>
27  
28 #define INET_PREFIXSTRLEN (INET_ADDRSTRLEN+3)
29 #define INET6_PREFIXSTRLEN (INET6_ADDRSTRLEN+4)
30  
31 static void print_usage()
32 {
33 fprintf(stderr, "Usage: 6rdcalc <v6 prefix>/<mask> <v4 address>/<mask>\n");
34 exit(1);
35 }
36  
37 static void print_error()
38 {
39 fprintf(stderr, "%s", strerror(errno));
40 exit(1);
41 }
42  
43 static void parse_str(int af, char *str, void *addr, unsigned long *mask)
44 {
45 int ret;
46 char *slash;
47  
48 /* Split the address at the slash. */
49 if ((slash = strchr(str, '/')) == NULL)
50 print_usage();
51 *slash = '\0';
52  
53 /* Parse the address. */
54 if ((ret = inet_pton(af, str, addr)) != 1) {
55 if (ret == 0)
56 print_usage();
57 else
58 print_error();
59 }
60  
61 /* Parse the mask. */
62 *mask = strtoul(slash+1, NULL, 10);
63 if ((af == AF_INET && *mask > 32) ||
64 (af == AF_INET6 && *mask > 128))
65 print_usage();
66 }
67  
68 int main(int argc, const char **argv)
69 {
70 char v6str[INET6_PREFIXSTRLEN], v4str[INET_PREFIXSTRLEN];
71 struct in6_addr v6;
72 struct in_addr v4;
73 unsigned long v6it, v4it, mask;
74 unsigned char *byte4, *byte6;
75 unsigned char bit4, bit6;
76  
77 /* Check parameters. */
78 if (argc != 3)
79 print_usage();
80  
81 /* Parse the v6 address. */
82 strncpy(v6str, argv[1], INET6_PREFIXSTRLEN);
83 v6str[INET6_PREFIXSTRLEN-1] = '\0';
84 parse_str(AF_INET6, v6str, &v6, &v6it);
85  
86 /* Parse the v4 address */
87 strncpy(v4str, argv[2], INET_PREFIXSTRLEN);
88 v6str[INET_PREFIXSTRLEN-1] = '\0';
89 parse_str(AF_INET, v4str, &v4, &v4it);
90  
91 /* Check if the combined mask is within bounds. */
92 mask = (32 - v4it) + v6it;
93 if (mask > 128)
94 print_usage();
95  
96 /* Combine the addresses. */
97 while (v4it < 32) {
98 byte6 = (unsigned char *)(&v6.s6_addr) + (v6it >> 3);
99 byte4 = (unsigned char *)(&v4.s_addr) + (v4it >> 3);
100 bit6 = 128 >> (v6it & 0x07);
101 bit4 = 128 >> (v4it & 0x07);
102  
103 if (*byte4 & bit4)
104 *byte6 |= bit6;
105 else
106 *byte6 &= ~bit6;
107  
108 v4it++; v6it++;
109 }
110  
111 /* Clear remaining bits. */
112 while (v6it < 128) {
113 byte6 = (unsigned char *)(&v6.s6_addr) + (v6it >> 3);
114 bit6 = 128 >> (v6it & 0x07);
115  
116 *byte6 &= ~bit6;
117  
118 v6it++;
119 }
120  
121 /* Print the subnet prefix. */
122 if (inet_ntop(AF_INET6, &v6, v6str, sizeof(v6str)) == NULL)
123 print_error();
124 printf("%s/%lu\n", v6str, mask);
125 return 0;
126 }