IPv6 Address Format

IPv6 Address Format
Unlike the usual dotted-decimal format of the IPv4 address, IPv6 is represented by hexadecimal
numbers. A hexadecimal number is equivalent to four bits, also known as a nibble because it is half
a byte, and is numbered 0–9 and A–F. A represents 10 and F represents 15, and they are not casesensitive.
The IPv6 address is a 32-digit hexadecimal numeric value, in eight four-digit clusters,
known as fields, separated by colons (:), representing the 128-bit address. Here is an example of a
valid IPv6 address: 1041:0000:130B:0000:0000:09C0:586C:1305.
There are some techniques used to shorten the IPv6 address. One of these techniques is to
omit leading 0s in the address field, so 0000 can be compressed to just 0 and 09C0 can be compressed
to 9C0. You can omit leading 0s but not trailing 0s. The previous IPv6 address example
TABLE 2 . 1 2 Decimal-to-Binary Chart
0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111
0000 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0001 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0010 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
0011 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63
0100 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79
0101 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
0110 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111
0111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127
1000 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143
1001 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159
1010 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175
1011 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191
1100 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207
1101 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223
1110 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239
1111 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255
68 Chapter 2  IP Addressing
could be shortened to 1041:0:130B:0:0:9C0:586C:1305. Another technique is to use double
colons (::) to represent a contiguous block of 0s. Again, the previous IPv6 address can be further
shortened to 1041:0:130B::9C0:586C:1305.
For some IPv6 addresses, this technique can really shorten the address. For example, the IPv6
address FF01:0:0:0:0:0:1 can be compressed to FF01::1. There is a limitation in using double
colons on the address. You can use it only once in any address, because if two double colons are
placed in the same address, there will be no way to identify the size of each block of 0s.
Let’s not forget about what is called the subnet mask in IPv4 terms but in the IPv6 world is
called the address prefix. The IPv6 prefix is used to distinguish which portion of the address represents
the network identifier. The slash (/) followed by the prefix length is the format used for
IPv6 and is the same format used by CIDR for IPv4 addresses. The prefix length is a decimal
value that indicates the number of high-order contiguous bits that comprise the network portion
of the IPv6 address. An example of using the prefix is 1041:0:130B::9C0:586C:1305/64.
If the IPv6 address ends in a double colon, it can be omitted. For example, the IPv6 address
8010:968:8680:265::/64 can be written as 8010:968:8680:265/64.
Now let’s talk about the three types of IPv6 addresses.