How to Calculate IPv6 Addresses

• One hex digit = 4 bits, one group = 16 bits
• Fixed (network) digits = prefix ÷ 4
• /64 subnets in a prefix = 2^(64 − prefix)
• Addresses in a prefix = 2^(128 − prefix)
• No broadcast, so no addresses are subtracted

Quick example: 2001:db8:abcd:12ab::1/56 has network 2001:db8:abcd:1200::/56 and holds 256 /64 subnets. Each step is explained below.

An IPv6 address is 128 bits written as eight hexadecimal groups separated by colons. Each group is 16 bits, or four hex digits (0–9 and a–f).

One hex digit is 4 bits, called a nibble. That is the key to IPv6 math: every digit is worth 4 bits of prefix.

1. Drop leading zeros in each group: 0db8 becomes db8, and 0000 becomes 0.
2. Replace one run of consecutive zero groups with ::. It may appear only once per address.
3. If there is more than one run of zeros, shorten the longest. On a tie, shorten the first.
4. A single zero group stays 0, and letters are lowercase (RFC 5952).

Expanding back to the full form

Count the groups that are left, then fill :: with zero groups until there are eight. 2001:db8:85a3::8a2e:370:7334 has 6 groups, so :: stands for 2 groups of 0000.

As in IPv4, an IPv6 prefix says how many bits from the left belong to the network. The difference is that a LAN is almost always a /64. The first 64 bits are the network, and the last 64 are an interface ID the device picks itself (SLAAC).

The formula: /64 subnets in a prefix = 2^(64 − prefix). A customer given a /56 can run 2⁸ = 256 separate /64 networks.

One /64 holds 2⁶⁴ = 18,446,744,073,709,551,616 addresses. That is why IPv6 planning counts subnets, not hosts.

Example: the address 2001:db8:abcd:12ab::1/56. Here is how to find its network and address range.

1. Write the address in full: 2001:0db8:abcd:12ab:0000:0000:0000:0001.
2. Divide the prefix by 4 to get the number of fixed digits: 56 ÷ 4 = 14 digits.
3. Keep the first 14 digits: 2001:0db8:abcd:12. Set the rest to 0 for the network, or to f for the last address.
4. The network is 2001:db8:abcd:1200::/56, and the last address is 2001:db8:abcd:12ff:ffff:ffff:ffff:ffff.
5. The /64 subnets inside run from 2001:db8:abcd:1200::/64 to 2001:db8:abcd:12ff::/64, which is 2⁸ = 256 subnets.

When the prefix is not a multiple of 4

For prefixes like /50 or /62, one digit is split down the middle. Write that digit in binary, keep as many bits as the prefix still needs, and zero the rest. For /62 on the same address: 62 = 15 × 4 + 2, so the 16th digit (b = 1011) keeps only its first two bits and becomes 1000 = 8. The network is 2001:db8:abcd:12a8::/62, which holds 2² = 4 /64 subnets.

IPv6 has no broadcast address. Multicast does that job, so no addresses are set aside for network and broadcast the way they are in IPv4.

• Mengenal IPv6 (Internet Protocol Version 6) dan Kelebihannya
• Mengenal Fungsi IPv6 pada Jaringan dan Perbedaannya dengan IPv4
• Dual Stack Network, Kelebihan, dan Perbedaannya dengan IPv4
• Apa Sih IP Address Itu? Yuk Cari Tau…