DHCPv6 (Dynamic Host Configuration Protocol version 6)

Last updated on Mar 24, 2023

DHCPv6, or Dynamic Host Configuration Protocol version 6, is a protocol used to automatically configure Internet Protocol version 6 (IPv6) hosts with IP addresses, network configuration information, and other parameters required for communication on an IPv6 network. In this article, we will explore DHCPv6 in detail, including its purpose, operation, and configuration.

Introduction to IPv6

Before we dive into DHCPv6, let's first review some basics of IPv6. IPv6 is the successor to IPv4, the original Internet Protocol that has been in use since the early days of the internet. One of the main drivers for the development of IPv6 was the exhaustion of IPv4 addresses, which are limited to just over four billion unique addresses. IPv6, on the other hand, uses a 128-bit address space, allowing for a virtually unlimited number of unique addresses.

In addition to the expanded address space, IPv6 includes a number of other improvements over IPv4, such as improved support for quality of service (QoS), simpler header format, and better security features.

Despite these improvements, IPv6 adoption has been slow. One of the reasons for this is that IPv6 requires a completely different infrastructure than IPv4, which has been in place for decades. As a result, transitioning to IPv6 can be a complex and costly process.

Purpose of DHCPv6

In an IPv6 network, hosts require certain configuration information to communicate with other devices. This includes an IP address, subnet mask, default gateway, DNS server addresses, and other parameters. In an IPv4 network, this configuration information is typically provided by a DHCP server.

Similarly, in an IPv6 network, DHCPv6 is used to provide configuration information to hosts. This includes IPv6 addresses, IPv6 prefixes, default routers, DNS server addresses, and other parameters.

DHCPv6 can be used in a variety of network configurations, including enterprise networks, service provider networks, and home networks. It can also be used in conjunction with other IPv6 configuration methods, such as Stateless Address Autoconfiguration (SLAAC), which we'll discuss in more detail later.

Operation of DHCPv6

DHCPv6 operates in a client-server model, where hosts act as clients and request configuration information from a DHCPv6 server. The DHCPv6 server is responsible for providing the requested information to the client.

When a host first joins an IPv6 network, it typically does not have any configuration information. The host sends out a DHCPv6 request message to locate a DHCPv6 server on the network. The request message is sent to the multicast address "ff02::1:2", which is the all-DHCPv6-servers multicast address.

When the DHCPv6 server receives the request message, it responds with a DHCPv6 advertisement message. This message includes the configuration information requested by the client, such as an IPv6 address, prefix, default router, DNS server address, and other options.

The client then sends a DHCPv6 request message to the server, confirming that it accepts the configuration information provided. The server responds with a DHCPv6 reply message, indicating that the client is now configured with the requested information.

DHCPv6 messages are encapsulated in IPv6 packets, using a source and destination address that is specific to the client and server. The messages also include transaction identifiers (TIDs) to ensure that the messages are properly matched between the client and server.

DHCPv6 Options

DHCPv6 options are used to provide additional configuration information to hosts. Options are included in DHCPv6 messages as variable-length fields, and are identified by a unique code. Some of the most common DHCPv6 options include:

IPv6 Address: This option is used to provide an IPv6 address to the client.
IPv6 Prefix: This option is used to provide an IPv6 prefix to the client, which can be used for Stateless Address Autoconfiguration (SLAAC).
Default Router: This option is used to provide the IPv6 address of the default router on the network.
DNS Server: This option is used to provide the IPv6 address of one or more DNS servers on the network.
Domain Name: This option is used to provide the domain name that is appended to unqualified domain names by the client.
Timezone: This option is used to provide the timezone offset for the client.
Vendor-Specific Information: This option is used to provide vendor-specific configuration information to the client.

DHCPv6 vs. SLAAC

In addition to DHCPv6, hosts can also obtain IPv6 addresses and other configuration information using Stateless Address Autoconfiguration (SLAAC). SLAAC is a method for hosts to automatically configure their own IPv6 addresses and default routers, without the need for a central DHCPv6 server.

In SLAAC, hosts use a combination of the IPv6 prefix provided by the router and their own unique identifier to generate a globally unique IPv6 address. The host also receives the IPv6 address of the default router on the network using Router Advertisement (RA) messages.

SLAAC can be used in conjunction with DHCPv6, or as a standalone configuration method. The decision to use DHCPv6, SLAAC, or a combination of both depends on the specific requirements of the network.

DHCPv6 Configuration

To configure a DHCPv6 server, several steps are required. First, the DHCPv6 server software must be installed on a server on the network. There are a variety of DHCPv6 server software options available, both open source and commercial.

Once the DHCPv6 server software is installed, the server must be configured with the appropriate network settings, such as the IPv6 address range to be used for DHCPv6 clients, the IPv6 prefix to be distributed to clients, and the DNS server addresses to be provided to clients.

DHCPv6 options can also be configured on the server, such as the domain name, timezone, and vendor-specific information.

Finally, DHCPv6 clients must be configured to request configuration information from the DHCPv6 server. This is typically done by configuring the network interface settings on the client to request an IPv6 address using DHCPv6.

Conclusion

DHCPv6 is a protocol used to automatically configure IPv6 hosts with IP addresses, network configuration information, and other parameters required for communication on an IPv6 network. DHCPv6 operates in a client-server model, where hosts request configuration information from a DHCPv6 server. DHCPv6 options are used to provide additional configuration information to hosts. DHCPv6 can be used in conjunction with Stateless Address Autoconfiguration (SLAAC), or as a standalone configuration method. To configure a DHCPv6 server, several steps are required, including installing the DHCPv6 server software, configuring the server settings, and configuring the DHCPv6 clients to request configuration information from the server.