is there any code for bitwise and ipv6 address and network mask (prefix)?

OK, I did this in C rather than C++, but it should work. Also, it uses bswap_64 which is AFAIK a GNU extension so may not work on everything.

It seems to be very quick on amd64, and faster than the current solution Yasar has come up with:

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <stdint.h> #include <arpa/inet.h> #if defined __GNUC__ && __GNUC__ >= 2 #include <byteswap.h> #else #error "Sorry, you need GNU for this" #endif struct split { uint64_t start; uint64_t end; }; void ipv6_prefix (unsigned char *masked, unsigned char *packed, int prefix) { struct split parts; uint64_t mask = 0; unsigned char *p = masked; memset(masked, 0, sizeof(struct in6_addr)); memcpy(&parts, packed, sizeof(parts)); if (prefix <= 64) { mask = bswap_64(bswap_64(parts.start) & ((uint64_t) (~0) << (64 - prefix))); memcpy(masked, &mask, sizeof(uint64_t)); return; } prefix -= 64; memcpy(masked, &(parts.start), sizeof(uint64_t)); p += sizeof(uint64_t); mask = bswap_64(bswap_64(parts.end) & (uint64_t) (~0) << (64 - prefix)); memcpy(p, &mask, sizeof(uint64_t)); } int main (int argc, char **argv) { unsigned char packed[sizeof(struct in6_addr)]; unsigned char masked[sizeof(struct in6_addr)]; char buf[INET6_ADDRSTRLEN], *p; int prefix = 56; if (argc < 2) return 1; if ((p = strchr(argv[1], '/'))) { *p++ = '\0'; prefix = atoi(p); } inet_pton(AF_INET6, argv[1], packed); ipv6_prefix(masked, packed, prefix); inet_ntop(AF_INET6, masked, buf, INET6_ADDRSTRLEN); printf("prefix = %s/%d\n", buf, prefix); return 0; } 

Calculate mask from prefix length:

struct sockaddr_in6 netmask; for (long i = prefixLength, j = 0; i > 0; i -= 8, ++j) netmask.sin6_addr.s6_addr[ j ] = i >= 8 ? 0xff : (ULONG)(( 0xffU << ( 8 - i ) ) & 0xffU ); 

Apply netmask to address, I derived this from inet_lnaof.

bool inet6_lnaof ( struct in6_addr* restrict dst, const struct in6_addr* restrict src, const struct in6_addr* restrict netmask ) { bool has_lna = FALSE; assert (NULL != dst); assert (NULL != src); assert (NULL != netmask); for (unsigned i = 0; i < 16; i++) { dst->s6_addr[i] = src->s6_addr[i] & netmask->s6_addr[i]; has_lna |= (0 != (src->s6_addr[i] & !netmask->s6_addr[i])); } return has_lna; } 

You can convert the address to binary in network byte order with inet_pton. Then set/clear the bits one byte at a time.

Threat the IP lik a 16 bytes array, skip the masked/8 bytes in the next byte mask the higher masked%8 bits, set the other ones to 0

int offset=masked/8; char remmask=0; int rem = masked%8; while(rem) { rem--; remmask|= 0x80>>rem; //0x80 is the highest bit in a byte set } offset++; (((char*)ipv6)+offset) &= remmask; while(offset<16) { (((char*)ipv6)+offset=0; offset++; } 

Wrote the code right here, so it hasn't been tested but I am thinking you could use something like this

I searched for this function but the above seem to complex so I wrote my own;

// Clear all bits above the prefix void mask_ipv6(struct in6_addr* a, unsigned prefix) { assert(prefix <= 128); unsigned bits_to_clear = 128 - prefix; unsigned i = 3; while (bits_to_clear >= 32) { a->s6_addr32[i] = 0; bits_to_clear -= 32; i--; } if (bits_to_clear == 0) return; uint32_t mask = htonl(~((1 << bits_to_clear) - 1)); a->s6_addr32[i] &= mask; } 

You may of course use a function name more of your liking.

this is quick and dirty solution, the source code is below if you want, use it. Warning ! the function assumes the IPv6 address is valid.

typedef uint16_t ip6_addr[8]; void ipv6_apply_mask(const char *ip6addr, unsigned int mask, ip6_addr ip6){ ip6_addr in_ip6; inet_pton(PF_INET6, ip6addr, ip6); for(int i = 0; i < 8; i++){ in_ip6[i] = ntohs(ip6[i]); } int index = (int) (mask / 16); int residue = mask % 16; if(residue == 0 && index == 8) return; switch(residue){ case 0:in_ip6[index++] = 0; break; case 1:in_ip6[index++]&=0x8000; break; case 2:in_ip6[index++]&=0xc000; break; case 3:in_ip6[index++]&=0xe000; break; case 4:in_ip6[index++]&=0xf000; break; case 5:in_ip6[index++]&=0xf800; break; case 6:in_ip6[index++]&=0xfc00; break; case 7:in_ip6[index++]&=0xfe00; break; case 8:in_ip6[index++]&=0xff00; break; case 9:in_ip6[index++]&=0xff80; break; case 10:in_ip6[index++]&=0xffc0; break; case 11:in_ip6[index++]&=0xffe0; break; case 12:in_ip6[index++]&=0xfff0; break; case 13:in_ip6[index++]&=0xfff8; break; case 14:in_ip6[index++]&=0xfffc; break; case 15:in_ip6[index++]&=0xfffe; break; } for (int i = index; i < 8; i++){ in_ip6[i] = 0; } for(int i = 0; i < 8; i++){ ip6[i] = htons(in_ip6[i]); } return; }