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.
Contents
- Port numbers
- DHCP Unique Identifier
- RFC 6939 Client Link Layer Address Option
- Example
- IETF standards
- References
IPv6 hosts may automatically generate IP addresses internally using stateless address autoconfiguration, 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.
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.
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 three types. The meaning of the remaining DUID depend on the type.
Three types are identified in RFC 3315 and further fourth is added by RFC 6355:
- 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)
RFC 6939 - Client Link-Layer Address Option
Due to the fact that it is difficult to manage multiple identifiers in a dual-stack environment, and the fact that DUID's 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. This option on DHCPv6 relays is not yet widely supported but some Cisco and Brocade switches support this option.
Example
In this example, 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.
[fe80::aabb:ccff:fedd:eeff]:546 for [ff02::1:2]:547.[fe80::0011:22ff:fe33:5566]:547 for [fe80::aabb:ccff:fedd:eeff]:546.[fe80::aabb:ccff:fedd:eeff]:546 for [ff02::1:2]:547. (Client messages are sent to the multicast address, per section 13 of RFC 3315.)[fe80::0011:22ff:fe33:5566]:547 for [fe80::aabb:ccff:fedd:eeff]:546.