IPv6 Subnet Masking


IPv6 subnet masking is similar to IPv4 with two key differences in the way IPv6 appear and what actually gets masked.

IPv6 uses 128 binary for each IP Address, as opposed to IPv4, which uses 32 binary digits. The 128 binary digits are divided into 16-bit words. Since using IPv4's octet notation to represent 128 bits would be difficult, we use a 16- digit hexadecimal numbering system instead.

Each IPv6 sets rep. Each IPv6 set represents 16 bits (4 characters at 4 bits each), and each 4-digit hex word represents 16 binary digits, for example:

  • Bin 0000000000000000 = Hex 000 (or just 0)
  • Bin 1111111111111111 = Hex FFFF
  • Bin 1101010011011011 = Hex D4DB


So, an IPv6 128-but binary address is represented by 8 hex words separated by colons:



With IPv4, every IP address comes with a corresponding subnet mask. IPv6 also uses subnets, but the subnet ID is built into the address. Every individual network segment requires at least one /64 prefix. The IPv6 equivalent to a IPv4 /24 subnet is a /64. This segment contains 64 network bits and 64 host bits. Regardless of hosts on an individual LAN or WAN segment, every multi-access network requires at least one /64 prefix.

Each character represents 4 bits (a nibble). A nibble boundary is a network mask that aligns on a 4-bit boundary. This makes it easier to understand and follow the IP address sequence, reducing incorrect configurations.

SolarWinds IP Address Manager (IPAM) provides a Subnet Allocation Wizard to help you efficiently organize your managed IP address space into subnets that are sized appropriately for the extent and traffic of your network.

The Subnet Allocation Wizard displays a list of available subnets. You can quickly choose from this interactive list to allocate new subnets on your network.