How does it work

Next, let's see how DHCPv6-PD works:

1. Role of ISP (Internet Service Provider)

In a typical DHCPv6-PD environment, the ISP plays an important role. The ISP has a large block of IPv6 addresses assigned through its address provider (RIR – Regional Internet Registry). This block is known as the ISP Allocation block.

2. Assignment to the client router

The customer router (also known as CPE – Customer Premises Equipment) connects to the ISP's network and has an external interface that obtains an IPv6 address via DHCPv6 from the ISP's infrastructure.

3. Prefix request

Once the client router has obtained its IPv6 address, it sends a prefix request (PD) to the ISP's DHCPv6 server. In this request, the client router requests a portion of the ISP's allocation block for its own network.

4. Prefix assignment

The ISP's DHCPv6 server, upon receiving the prefix request, evaluates its allocation block and assigns a prefix (sub-block) of it to the client router. This prefix will be used by the client router to assign IPv6 addresses to its own interfaces and internal subnets.

5. Client router configuration

Using the prefix assigned by the ISP's DHCPv6 server, the client router divides this prefix into smaller subnets based on the needs of its own internal network. Then, it configures its internal interfaces and subnets with the corresponding IPv6 addresses.

6. Internal address distribution

Once the client router has divided the received prefix into internal subnets, it can use SLAAC or DHCPv6 to assign IPv6 addresses to devices on its internal networks.

7. Renewal and update

Prefixes assigned via DHCPv6-PD can have a certain time to live (TTL – Time to Live) after which they must be renewed or updated. The customer's router must keep an eye on renewals and updates to ensure that the IPv6 addresses on its internal network remain valid and up-to-date as assigned by the ISP.

In short, DHCPv6-PD is an extension of the DHCPv6 protocol that allows routers to obtain blocks of IPv6 addresses (prefixes) from the ISP for their own network and, from there, partition and assign addresses to their internal subnets.

This is especially useful in Internet service provider environments and in networks that require an IPv6 addressing hierarchy to subdivide a block of addresses into smaller subnets.