Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6
obsoleted by
- rfc-8415 — Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Extracted elements (18)
A node may include a Client Identifier option in the Information-request message to identify itself, because the server administrator may want to customize the server's response to each node based on node identity. However, this is not required.
RFC 3315 does not define mechanisms to control when a host uses Information-request messages to obtain updated configuration parameters; the DHC WG was tasked with developing such mechanisms to be published as Standards-track RFCs.
Stateless DHCP is used by nodes that have already obtained IPv6 addresses through other mechanisms (such as stateless address autoconfiguration) and need only configuration information like DNS server addresses. The server is called 'stateless' because it need not maintain any dynamic state for individual clients.
In networks with both stateless address autoconfiguration clients using DHCP only for DNS and clients using DHCP for stateful address assignment, stateless-only DHCP servers may receive stateful messages due to relay agent configuration. Stateless servers must silently discard these non-Information-Request messages.
The operation of relay agents is identical for stateless and stateful DHCP service. A network element can simultaneously provide stateless DHCP service to hosts needing only configuration and relay stateful address-assignment messages to another DHCP server.
A DHCP server that is only able to provide stateless configuration information through an Information-request/Reply message exchange MUST discard any other DHCP messages it receives, specifically any messages other than Information-Request or Relay-forward.
A stateless-only DHCP server must not participate in any stateful address configuration message exchanges. If other DHCP servers are configured to provide stateful address assignment, one of those servers will provide address assignment.
Optional options for stateless DHCP include: Preference (server preference level), Elapsed time (time since client began configuration), User Class, Vendor Class, Vendor-specific Information, Client Identifier, and Authentication. Clients are not required to send the Client Identifier; servers echo it back if included.
Relay-forward is sent by a DHCP relay agent to carry the client message to a server (RFC 3315 section 15.13). Relay-reply is sent by a DHCP server to carry a response message back to the relay agent (RFC 3315 section 15.14).
The DNS Recursive Name Servers option specifies the DNS recursive name servers the client uses for name resolution (RFC 3646). The DNS search list option specifies domain names to be searched during name resolution. Both are primary configuration options for stateless DHCP.
The Information-request message is the primary client-to-server message in stateless DHCP. The client includes an Option Request option specifying the configuration options it wishes to receive, such as DNS recursive name server addresses.
The Interface-ID option is sent by the DHCP relay agent and returned by the server to identify the interface to be used when forwarding a message to the client (RFC 3315 section 22.18). It is required for relay agents in stateless DHCP service.
The Option Request option specifies the configuration information the client is requesting from the server (RFC 3315 section 22.7). This option is required for both clients and servers implementing stateless DHCP service.
The Reply message is sent by a DHCP server to a client containing the requested configuration parameters (RFC 3315 sections 18.2.6 and 18.2.8). It carries configuration data such as DNS recursive name servers and SIP servers.
The SIP Servers option specifies the SIP servers the client uses to obtain a list of domain names or IPv6 addresses that can be mapped to one or more SIP outbound proxy servers (RFC 3319). This is a standard configuration option for stateless DHCP.
The Status Code option is used to indicate completion status or other status information (RFC 3315 section 22.13). The Server Identifier option is used to identify the server responding to a client request (RFC 3315 section 22.3). Both are required for stateless DHCP service.
Authenticated DHCP, as described in sections 21 and 22.11 of the DHCP specification (RFC 3315), can be used to avoid attacks mounted through the stateless DHCP service. The Authentication option (RFC 3315 section 21) is available as an optional element for stateless DHCP implementations.
Stateless DHCP service introduces no additional security considerations beyond those discussed in sections 21, 22.11, and 23 of RFC 3315. Configuration information provided through stateless DHCP may be used to mount spoofing, man-in-the-middle, denial-of-service, and other attacks.