DHCPv6

The Dynamic Host Configuration Protocol version 6 (DHCPv6) is a network protocol for configuring Internet Protocol version 6 (IPv6) hosts with IP addresses, IP prefixes and other configuration data required to operate in an IPv6 network. It is the IPv6 equivalent of the Dynamic Host Configuration Protocol for IPv4.

Internet protocol suite
Application layer
Transport layer
Internet layer
Link layer
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IPv6 hosts may automatically generate IP addresses internally using stateless address autoconfiguration (SLAAC), or they may be assigned configuration data with DHCPv6.

IPv6 hosts that use stateless autoconfiguration may require information other than an IP address or route. DHCPv6 can be used to acquire this information, even though it is not being used to configure IP addresses. DHCPv6 is not necessary for configuring hosts with the addresses of Domain Name System (DNS) servers, because they can be configured using Neighbor Discovery Protocol, which is also the mechanism for stateless autoconfiguration.[1]

Many IPv6 routers, such as routers for residential networks, must be configured automatically with no operator intervention. Such routers require not only an IPv6 address for use in communicating with upstream routers, but also an IPv6 prefix for use in configuring devices on the downstream side of the router. DHCPv6 prefix delegation provides a mechanism for configuring such routers.

Operation

Port numbers

DHCPv6 uses UDP port number 546 for clients and port number 547 for servers.

DHCP unique identifier

The DHCP unique identifier (DUID) is used by a client to get an IP address from a DHCPv6 server. It has a 2-byte DUID type field, and a variable-length identifier field up to 128 bytes. Its actual length depends on its type. The server compares the DUID with its database and delivers configuration data (address, lease times, DNS servers, etc.) to the client. The first 16 bits of a DUID contain the DUID type, of which there are four types. The meaning of the remaining DUID depends on the type.

Four types are identified in RFC 8415:

  • Link-layer address plus time (DUID-LLT)
  • Vendor-assigned unique ID based on enterprise number (DUID-EN)
  • Link-layer address (DUID-LL)
  • UUID-based DUID (DUID-UUID)

Due to the fact that it is difficult to manage multiple identifiers in a dual-stack environment, and the fact that DUIDs are simply not optimal for some situations, RFC 6939 was released, giving a way to identify a host based on its MAC address. It defines a way for a DHCPv6 relay to pass that information to a DHCPv6 server.

Example

In this example, without rapid-commit present, the server's link-local address is fe80::0011:22ff:fe33:5566 and the client's link-local address is fe80::aabb:ccff:fedd:eeff.

  • Client sends a solicit from [fe80::aabb:ccff:fedd:eeff]:546 to [ff02::1:2]:547. (Client messages are sent to the multicast address, per section 14 of RFC 8415.)
  • Server replies with an advertise from [fe80::0011:22ff:fe33:5566]:547 to [fe80::aabb:ccff:fedd:eeff]:546.
  • Client replies with a request from [fe80::aabb:ccff:fedd:eeff]:546 to [ff02::1:2]:547.
  • Server finishes with a reply from [fe80::0011:22ff:fe33:5566]:547 to [fe80::aabb:ccff:fedd:eeff]:546.

IETF standards
  • RFC 3319, "Dynamic Host Configuration Protocol (DHCPv6) Options for Session Initiation Protocol (SIP) Servers"
  • RFC 3646, "DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6)"
  • RFC 4704, "The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN) Option"
  • RFC 5007, "DHCPv6 Leasequery"
  • RFC 6221, "Lightweight DHCPv6 Relay Agent" (LDRA) - Updates RFC 3315, Errata
  • RFC 6355, "Definition of the UUID-Based DHCPv6 Unique Identifier (DUID-UUID)"
  • RFC 6939, "Client Link-Layer Address Option in DHCPv6"
  • RFC 8415, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)" - Obsoletes RFC 3315, RFC 3633, RFC 3736, RFC 4242, RFC 7083, RFC 7283, RFC 7550.

See also

References
  1. RFC 4339, IPv6 Host Configuration of DNS Server Information Approaches, J. Jeong (February 2006)
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