`
Prefix length is stated in classless inter-domain routing (CIDR) notation. CIDR notation is a slash at the end of the address that is followed by the prefix length in bits. For information on CIDR format IP addresses, refer to Designing Your CIDR IPv4 Addressing Scheme.
The site prefix of an IPv6 address occupies up to 48 of the leftmost bits of the IPv6 address. For example, the site prefix of the IPv6 address `2001:db8:3c4d:0015:0000:0000:1a2f:1a2b/48` is contained in the leftmost 48 bits, `2001:db8:3c4d`. You use the following representation, with zeros compressed, to represent this prefix:
`2001:db8:3c4d::/48`
You can also specify a subnet prefix, which defines the internal topology of the network to a router. The example IPv6 address has the following subnet prefix.
`2001:db8:3c4d:15::/64`
The subnet prefix always contains 64 bits. These bits include 48 bits for the site prefix, in addition to 16 bits for the subnet ID.
Source: [IPv6 Addressing Overview (oracle.com)](https://docs.oracle.com/cd/E19253-01/816-4554/6maoq01od/index.html)
The prefix 2001:db8::/32 is a special IPv6 prefix that is used specifically for documentation examples.
## Features
### Prefix Delegation
> Since it would not be practical to manually provision networks at scale, in IPv6 networking, DHCPv6 prefix delegation is used to assign a network address prefix and automate configuration and provisioning of the public routable addresses for the network. The way this works for example in case of a home network is that the home router uses DHCPv6 protocol to request a network prefix from the ISP's DHCPv6 server. Once assigned, the ISP routes this network to the customer's home router and the home router starts advertising the new addresses to hosts on the network, either via SLAAC or using DHCPv6.
Source: [Prefix Delegation (wikipedia.com)](https://en.wikipedia.org/wiki/Prefix_delegation)
### Neighbor Discover Protocol (NDP)
> The Neighbor Discovery Protocol (NDP, ND) is a protocol in the Internet protocol suite used with Internet Protocol Version 6 (IPv6). It operates at the link layer of the Internet model, and is responsible for gathering various information required for internet communication, including the configuration of local connections and the domain name servers and gateways used to communicate with more distant systems.
The protocol defines five different ICMPv6 packet types to perform functions for IPv6 similar to the Address Resolution Protocol (ARP) and Internet Control Message Protocol (ICMP) Router Discovery and Router Redirect protocols for IPv4. However, it provides many improvements over its IPv4 counterparts (RFC 4861, section 3.1). For example, it includes Neighbor Unreachability Detection (NUD), thus improving robustness of packet delivery in the presence of failing routers or links, or mobile nodes.
Source: [Neighbor Discovery Protocol (wikipedia.com)](https://en.wikipedia.org/wiki/Neighbor_Discovery_Protocol)
### Stateless address autoconfiguration (SLAAC)
> IPv6 hosts configure themselves automatically. Every interface has a self-generated link-local address and, when connected to a network, conflict resolution is performed and routers provide network prefixes via router advertisements. Stateless configuration of routers can be achieved with a special router renumbering protocol. When necessary, hosts may configure additional stateful addresses via Dynamic Host Configuration Protocol version 6 (DHCPv6) or static addresses manually.
Source: [Stateless address autoconfiguration (SLAAC) (wikipedia.com)](https://en.wikipedia.org/wiki/IPv6#Stateless_address_autoconfiguration_(SLAAC))