IPv6 Subnetting - Internet Protocol version 6 (IPv6)

What is IPv6 Subnetting?

In IPv4, classes created the addresses. The bits used for network prefixes and the bits used for the hosts on that network are clearly defined by the Classful IPv4. For subnetting, the default classful netmask allow to borro the host bits used as the subnet bits resulting in multiple subnets and each subnet has less hosts. In the sense that lesser bits are used for host addresses if host bits are used for creating a subnet.

128 bits are used by IPv6 for representing address that includes bits that are to be used for subnetting. The hosts use the second half (64 bits) of the address.


16 bits of subnet equals to IPv4 class of B network. These subnet bits are used by an organization for having another 65 thousands of subnets which is more than enough.

Thus routing prefix is /64 and host portion is 64 bits. The network can be subnetted beyond 16 bits of subnet ID by borrowing the host bits. It is always recommended that host addresses should use 64 bits since 64 bits are required for auto-configuration.

IPv6 subnetting works on the same concept as Variable Length Subnet Masking in IPv4.

/48 prefix can be allocated to an organization providing it the benefit of having up to /64 subnet prefixes, which is 65535 sub-networks, each having 264hosts. Where there are only two hosts on a link or IPv6 enabled devices, a /64 prefix can be assigned to a point-to-point connection.

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Internet Protocol version 6 (IPv6) Topics