Internet Engineering Task Force J. Bound INTERNET DRAFT Compaq Computer Corp. DHC Working Group C. Perkins Obsoletes: draft-ietf-dhc-dhcpv6-13.txt Sun Microsystems Laboratories 25 February 1999 Dynamic Host Configuration Protocol for IPv6 (DHCPv6) draft-ietf-dhc-dhcpv6-14.txt Status of This Memo This document is a submission by the Dynamic Host Configuration Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the dhcp-v6@bucknell.edu mailing list. Distribution of this memo is unlimited. This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at: http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at: http://www.ietf.org/shadow.html. Abstract The Dynamic Host Configuration Protocol (DHCPv6) enables DHCP servers to pass configuration information, via extensions, to IPv6 nodes. It offers the capability of automatic allocation of reusable network addresses and additional configuration flexibility. This protocol is a stateful counterpart to the IPv6 Stateless Address Autoconfiguration protocol, and can be used separately or together with the latter to obtain configuration information. Bound, Perkins Expires 25 August 1999 [Page i]
Internet Draft DHCP Version 6 25 February 1999 Contents Status of This Memo i Abstract i 1. Introduction 1 2. Terminology and Definitions 2 2.1. IPv6 Terminology . . . . . . . . . . . . . . . . . . . . 2 2.2. DHCPv6 Terminology . . . . . . . . . . . . . . . . . . . 3 2.3. Specification Language . . . . . . . . . . . . . . . . . 4 2.4. Error Values . . . . . . . . . . . . . . . . . . . . . . 4 3. Protocol Design Model 4 3.1. Design Goals . . . . . . . . . . . . . . . . . . . . . . 4 3.2. DHCP Messages . . . . . . . . . . . . . . . . . . . . . . 5 3.3. Request/Response Processing Model . . . . . . . . . . . . 7 4. DHCP Message Formats and Field Definitions 8 4.1. DHCP Solicit Message Format . . . . . . . . . . . . . . . 8 4.2. DHCP Advertise Message Format . . . . . . . . . . . . . . 9 4.3. DHCP Request Message Format . . . . . . . . . . . . . . . 10 4.4. DHCP Reply Message Format . . . . . . . . . . . . . . . . 12 4.5. DHCP Release Message Format . . . . . . . . . . . . . . . 13 4.6. DHCP Reconfigure Message Format . . . . . . . . . . . . . 15 5. DHCP Client Considerations 16 5.1. Verifying Resource Allocations After Restarts . . . . . . 16 5.2. Sending DHCP Solicit Messages . . . . . . . . . . . . . . 16 5.3. Receiving DHCP Advertise Messages . . . . . . . . . . . . 17 5.4. Sending DHCP Request Messages . . . . . . . . . . . . . . 18 5.5. Receiving DHCP Reply Messages . . . . . . . . . . . . . . 20 5.6. Sending DHCP Release Messages . . . . . . . . . . . . . . 20 5.7. Receiving DHCP Reconfigure Messages . . . . . . . . . . . 21 5.8. Interaction with Stateless Address Autoconfiguration . . 22 6. DHCP Server Considerations 23 6.1. Receiving DHCP Solicit Messages . . . . . . . . . . . . . 23 6.2. Sending DHCP Advertise Messages . . . . . . . . . . . . . 24 6.3. DHCP Request and Reply Message Processing . . . . . . . . 24 6.3.1. Processing for Extensions to DHCP Request and Reply Messages . . . . . . . . . . . . . . . . . 25 6.3.2. Client Requests to Deallocate Unknown Resources . 26 6.4. Receiving DHCP Release Messages . . . . . . . . . . . . . 26 6.5. Sending DHCP Reconfigure Messages . . . . . . . . . . . . 27 Bound, Perkins Expires 25 August 1999 [Page ii]
Internet Draft DHCP Version 6 25 February 1999 6.6. Client-Resource timeouts . . . . . . . . . . . . . . . . 28 7. DHCP Relay Considerations 28 7.1. DHCP Solicit and DHCP Advertise Message Processing . . . 28 7.2. DHCP Request Message Processing . . . . . . . . . . . . . 29 7.3. DHCP Reply Message Processing . . . . . . . . . . . . . . 30 8. Retransmission and Configuration Variables 30 9. Security Considerations 33 10. Year 2000 considerations 33 11. IANA Considerations 34 12. Acknowledgements 34 A. Changes for this revision 34 B. Related Protocol Specifications 35 C. Comparison between DHCPv4 and DHCPv6 37 D. Full Copyright Statement 40 Chair's Address 43 Author's Address 43 Bound, Perkins Expires 25 August 1999 [Page iii]
Internet Draft DHCP Version 6 25 February 1999 1. Introduction The Dynamic Host Configuration Protocol (DHCPv6, or in this document usually DHCP) provides configuration parameters to Internet nodes. DHCP consists of a protocol for delivering node-specific configuration parameters from a DHCP server to a client, and extensions for allocation of network addresses and other related parameters to IPv6 [7] nodes. DHCP uses a client-server model, where designated DHCP servers automatically allocate network addresses and deliver configuration parameters to dynamically configurable clients. Throughout the remainder of this document, the term "server" refers to a node providing initialization parameters by way of the DHCP protocol, and the term "client" refers to a node requesting initialization parameters from a DHCP server. DHCPv6 uses Request and Reply messages to support a client/server processing model whereby both client and server are assured that requested configuration parameters have been received and accepted by the client. DHCP supports optional configuration parameters and processing for nodes through extensions described in its companion document ``Extensions for the Dynamic Host Configuration Protocol for IPv6'' [15]. The IPv6 Addressing Architecture [9] and IPv6 Stateless Address Autoconfiguration [20] specifications provide new features not available in IP version 4 (IPv4) [18], which are used to simplify and generalize the operation of DHCP clients. This document is intended to complement those specifications for clients attached to the kinds of Internet media for which those specifications apply. In particular, the specification in this document does not necessarily apply to nodes which do not enjoy a bidirectional link to the Internet. Section 2 provides definitions for terminology used throughout this document. Section 3 provides an overview of the protocol design model that guided the design choices in the specification; section 3.2 briefly describes the protocol messages and their semantics. Section 4 provides the message formats and field definitions used for each message. Sections 5, 6, and 7 specify how clients, servers, and relays respectively interact. The timeout and retransmission guidelines as well as configuration variables for DHCP protocol operations are discussed in Section 8. Appendix B summarizes related work in IPv6 that will provide helpful context; it is not part of this specification, but included for informational purposes. Appendix C discusses the differences between DHCPv4 and DHCPv6. Bound, Perkins Expires 25 August 1999 [Page 1]
Internet Draft DHCP Version 6 25 February 1999 2. Terminology and Definitions Relevant terminology from the IPv6 Protocol [7], IPv6 Addressing Architecture [9], and IPv6 Stateless Address Autoconfiguration [20] is given, followed by DHCPv6 terminology. 2.1. IPv6 Terminology address An IP layer identifier for an interface or a set of interfaces. unicast address An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address. multicast address An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces identified by that address. host Any node that is not a router. IP Internet Protocol Version 6 (IPv6). The terms IPv4 and IPv6 are used only in contexts where it is necessary to avoid ambiguity. interface A node's attachment to a link. link A communication facility or medium over which nodes can communicate at the link layer, i.e., the layer immediately below IP. Examples are Ethernet (simple or bridged); Token Ring; PPP links, X.25, Frame Relay, or ATM networks; and internet (or higher) layer "tunnels", such as tunnels over IPv4 or IPv6 itself. link-layer identifier a link-layer identifier for an interface. Examples include IEEE 802 addresses for Ethernet or Token Ring network interfaces, and E.164 addresses for ISDN links. link-local address An IP address having link-only scope, indicated by having the routing prefix (FE80::0000/64), that can be used to reach neighboring nodes attached to the same link. Every interface has a link-local address. Bound, Perkins Expires 25 August 1999 [Page 2]
Internet Draft DHCP Version 6 25 February 1999 message A unit of data carried in a packet, exchanged between DHCP agents and clients. neighbor A node attached to the same link. node A device that implements IP. packet An IP header plus payload. prefix A bit string that consists of some number of initial bits of an address. router A node that forwards IP packets not explicitly addressed to itself. 2.2. DHCPv6 Terminology agent address The address of a neighboring DHCP Agent on the same link as the DHCP client. binding A binding (or, client binding) containing the data which a DHCP server maintains for each of its clients (see Section 6). resource-server association An association between a resource and a DHCP server, maintained by the client which received that resource from that DHCP server. configuration parameter Any parameter that can be used by a node to configure its network subsystem and enable communication on a link or internetwork. DHCP client (or client) A node that initiates requests on a link to obtain configuration parameters. DHCP server (or server) A server is a node that responds to requests from clients, and may or may not be on the same link as as the client. DHCP relay (or relay) A node that acts as an intermediary to deliver DHCP messages between clients and servers, and is on the same link as a client. Bound, Perkins Expires 25 August 1999 [Page 3]
Internet Draft DHCP Version 6 25 February 1999 DHCP agent (or agent) Either a DHCP server on the same link as a client, or a DHCP relay. transaction-ID An unsigned integer to match responses with replies initiated either by a client or server. Clients MUST use integers from 1 to 1000, and servers use integers greater than 1000 for transaction-ID's. 2.3. Specification Language In this document, the words MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY are used to signify the requirements of the specification, in accordance with RFC 2119 [2]. 2.4. Error Values This specification document uses symbolic names for the errors known to DHCP clients and servers, as used for instance in the status field of the DHCP Reply message (see section 4.4). The symbolic names have the actual values listed below: Error Name ErrorID ================================ PoorlyFormed 18 Unavail 19 NoBinding 20 InvalidSource 21 NoServer 23 ICMPError 64 3. Protocol Design Model This section is provided for implementors to understand the DHCPv6 protocol design model from an architectural perspective. Goals and conceptual models are presented in this section. 3.1. Design Goals The following list gives general design goals for this DHCP specification. Bound, Perkins Expires 25 August 1999 [Page 4]
Internet Draft DHCP Version 6 25 February 1999 - DHCP should be a mechanism rather than a policy. DHCP must allow local system administrators control over configuration parameters where desired; e.g., local system administrators should be able to enforce local policies concerning allocation and access to local resources where desired. - DHCP must not require manual configuration of DHCP clients, except as dictated by security requirements. Each node should be able to obtain appropriate local configuration parameters without user intervention. - DHCP must not require a server on each link. To allow for scale and economy, DHCP must work across DHCP relays. - In some installations, clients on certain subnets can be served by more than one DHCP server, improving reliability and/or performance. Therefore, a DHCP client must be prepared to receive multiple (possibly different) responses to a DHCP Solicit message. - DHCP must coexist with statically configured, non-participating nodes and with existing network protocol implementations. - DHCPv6 must be compatible with IPv6 Stateless Address Autoconfiguration [20]. - A DHCPv6 Client implementation may be started in the absence of any IPv6 routers on the client's link. - DHCP architecture must support automated renumbering of IP addresses [3]. - DHCP servers should be able to support Dynamic Updates to DNS [22]. - DHCP servers must be able to support multiple IPv6 addresses for each client. On the other hand, a DHCP server to server protocol is NOT part of this specification. Furthermore, it is NOT a design goal of DHCP to specify how a server configuration parameter database is maintained or determined. Methods for configuring DHCP servers are outside the scope of this document. 3.2. DHCP Messages Each DHCP message contains a type, which defines its function within the protocol. Formats for the messages are found in section 4, with Bound, Perkins Expires 25 August 1999 [Page 5]
Internet Draft DHCP Version 6 25 February 1999 an initial description and discussion. Processing details for these DHCP messages are specified in Sections 5, 6, and 7. The message types are as follows: 01 DHCP Solicit The DHCP Solicit message is an IP multicast message sent by a client to one or more agents, or forwarded by a relay to one or more servers. 02 DHCP Advertise The DHCP Advertise is an IP unicast message sent by a DHCP Agent in response to a client's DHCP Solicit message. 03 DHCP Request The DHCP Request is an IP unicast message sent by a client to a server to request configuration parameters on a network. 04 DHCP Reply The DHCP Reply is an IP unicast message sent by a server in response to a client's DHCP Request, or by the relay that relayed that client's DHCP Request. Extensions [15] to the DHCP Reply describe the resources that the server has committed and allocated to this client, and may contain other information for use by this client. 05 DHCP Release The DHCP Release is an IP unicast message sent by a client to inform the server that the client is releasing resources. 06 DHCP Reconfigure The DHCP Reconfigure is an IP unicast or multicast message sent by a server to inform one or more clients that the server has new configuration information of importance to the client. Each client is expected to initiate a new DHCP Request in response to the Reconfiure message. DHCP message types not defined here (msg-types 0 and 7-255) are reserved and SHOULD be silently ignored. Bound, Perkins Expires 25 August 1999 [Page 6]
Internet Draft DHCP Version 6 25 February 1999 3.3. Request/Response Processing Model The request/response processing for DHCPv6 is transaction based and uses a set of best-effort messages to complete the transaction. To find a server, a client sends a DHCP Solicit from the interface which it wishes to configure. The client then awaits a DHCP Advertise message containing an IP address of a DHCP server. Transactions are started by a client with a DHCP Request, which may be issued after the client knows the server's address. The server then unicasts a DHCP Reply, possibly via a relay. At this point in the flow all data has been transmitted and is presumed to have been received. To provide a method of recovery if either the client or server does not receive its messages, the client retransmits each DHCP Request message until it elicits the corresponding DHCP Reply, or until it can be reasonably certain that the desired DHCP server is unavailable, or it determines that it does not want a response (i.e., it MAY abort the transaction). The timeout and retransmission guidelines and configuration variables are discussed in Section 8. DHCP uses UDP [17] to communicate between clients and servers. UDP is not reliable, but the DHCP retransmission scheme just described provides reliability between clients and servers. The following well-known multicast addresses are used by DHCP agents and clients: FF02:0:0:0:0:0:1:2 All DHCP Agents (servers and relays) MUST join the link-local All-DHCP-Agents multicast group at the address FF02:0:0:0:0:0:1:2. FF05:0:0:0:0:0:1:3 All DHCP servers MUST join the site-local All-DHCP-Servers multicast group at the address FF05:0:0:0:0:0:1:3. FF05:0:0:0:0:0:1:4 All DHCP relays MUST join the site-local All-DHCP-Relays multicast group at the address FF05:0:0:0:0:0:1:4. A DHCP server or agent MUST transmit all messages to DHCP clients on UDP port 546. A DHCP client MUST transmit all messages to a DHCP agent over UDP using port 547. A DHCP server MUST transmit all messages to DHCP relays over UDP on port 546. The source port for DHCP messages is arbitrary. For the proper operation of the DHCP protocol to operate within a network where one or more firewallsare used, DHCP transactions sent to the IP addresses of DHCP servers at UDP destination ports 546 and 547 will need to be permitted. Bound, Perkins Expires 25 August 1999 [Page 7]
Internet Draft DHCP Version 6 25 February 1999 4. DHCP Message Formats and Field Definitions All reserved fields in a message MUST be transmitted as zeroes and ignored by the receiver of the message. 4.1. DHCP Solicit Message Format A client transmits a DHCP Solicit message over the interface to be configured, to obtain one or more server addresses. Unless otherwise noted, the value of all fields are set by the client. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-type = 1 |C| reserved | prefix-size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | client's link-local address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | relay-address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | saved agent-address | | (if present, 16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ C If set, the client requests that all servers receiving the message deallocate the resources associated with the client. If set, the client SHOULD provide a saved agent-address to locate the clients binding by a server. prefix-size A nonzero prefix-size is the number of leftmost bits of the agent's IPv6 address which make up the routing prefix. The prefix-size field is set by the DHCP relay if the relay receives the solicitation and forwards it to one or more DHCP Servers. reserved 0 client's link-local address The IP link-local address of the client interface from which the client issued the DHCP Request message relay-address Set by the client to be zero. If received by a DHCP relay, set by the relay to the IP address of the Bound, Perkins Expires 25 August 1999 [Page 8]
Internet Draft DHCP Version 6 25 February 1999 interface on which the relay received the client's DHCP Solicit message saved agent-address If present, the IP address of an agent's interface retained by the client from a previous DHCP transaction. A client SHOULD send a DHCP Solicit message to the All-DHCP-Agents multicast group (see section 3.3), setting the relay-address to zero. Any relay receiving the solicitation MUST forward it to the All-DHCP-Servers multicast group. In that case, the relay MUST copy a non-link-local address of its interface from which the client's solicitation was received into the relay-address field. Servers receiving the solicitation then send their advertisements to the prospective client. 4.2. DHCP Advertise Message Format A DHCP agent sends a DHCP Advertise message to inform a prospective client about the IP address of a server to which a DHCP Request message may be sent. When the client and server are on different links, the server sends the advertisement back through the relay whence the solicitation came. The value of all fields in the DHCP Adverstise message are filled in by the DHCP Server and not changed by any DHCP Relay. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-type = 2 |S| reserved | preference | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | client's link-local address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | agent-address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | server-address | | (16 octets, if present) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | extensions (variable number and length) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ S If set, the server-address is present. reserved 0 Bound, Perkins Expires 25 August 1999 [Page 9]
Internet Draft DHCP Version 6 25 February 1999 preference An octet (unsigned) indicating a server's willingness to provide service to the client (see Section 5.3). client's link-local address The IP link-local address of the client interface from which the client issued the DHCP Request message agent-address The IP address of a DHCP Agent interface on the same link as the client. server-address If present, the IP address of the DHCP server extensions See [15]. Suppose that a server on the same link as a client issues the DHCP Advertise in response to a DHCP Solicit message sent to the All-DHCP-Agents multicast address. Then the agent-address will be an IP address of one of the server's interfaces on the same link as the client, and the `S' bit will be set to zero, indicating the absence of the server-address in the DHCP Advertise message. See section 5.3 for information about how clients handle the preference field. The server MUST copy the client's link-local address into the advertisement which is sent in response to a DHCP Solicit. Both server-address (if present) and agent-address of the DHCP Advertise message MUST have sufficient scope to be reachable by the client. Moreover, the agent-address of any DHCP Advertise message sent by a relay MUST NOT be a link-local address. In situations where there are no routers sending Router Advertisements, then a DHCP server MUST be configured on the same link as prospective clients. The DHCPv6 protocol design does not apply to situations where the client is unable to route messages to a server not on the same link. 4.3. DHCP Request Message Format In order to request configuration parameters from a server, a client sends a DHCP Request message, and MAY append extensions [15]. If the client does not know any server address, it MUST first obtain one by multicasting a DHCP Solicit message (see Section 4.1). Typically, when a client reboots, it does not have a valid IP address of sufficient scope for the server to communicate with the client. In such cases, the client MUST NOT send the message directly to the server because the server could not return any response to the client; the client MUST send the message to the local relay and insert the relay-address as the agent-address in the message header. Bound, Perkins Expires 25 August 1999 [Page 10]
Internet Draft DHCP Version 6 25 February 1999 Otherwise, the client MAY omit the server-address in the DHCP Request message; in this case, the client MUST clear the S-bit and send the message directly to the server, using the server's address as the IP destination address in the IP header. In either case, all fields in the DHCP Request message are entered by the client. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-type = 3 |C|S|R| rsvd | transaction-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | client's link-local address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | agent-address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | server-address | | (16 octets, if present) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | extensions (variable number and length) .... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ C If set, the client requests the server to remove all resources associated with the client binding, except those resources provided as extensions. S If set, the server-address is present R If set, the client has rebooted and requests that all of its previous transaction-IDs be expunged and made available for re-use. rsvd 0 transaction-ID A unsigned integer identifier used to identify this Request. client's link-local address The IP link-local address of the client interface from which the client issued the DHCP Request message agent-address The IP address of an agent's interface, copied from a DHCP Advertisement message. Bound, Perkins Expires 25 August 1999 [Page 11]
Internet Draft DHCP Version 6 25 February 1999 server-address If present, the IP address of the server which should receive the client's DHCP Request message. extensions See [15]. When the client sets the `C' bit and adds extensions, the server is expected to deallocate all other resources not listed in the extension. The resources explicitly requested in extensions to the Request message SHOULD be reallocated by the server to the client, assuming the client is still authorized to receive them. The transaction-ID is selected by the client to be greater than or equal to 1024, unless the DHCP Request is sent in response to a Reconfigure msg (see section 4.6). In that case, the transaction-ID is copied from the transaction-ID in the Reconfigure message. 4.4. DHCP Reply Message Format The server sends one DHCP Reply message in response to every DHCP Request or DHCP Release received. If the request comes with the `S' bit set, the client could not directly send the Request to the server and had to use a neighboring relay agent. In that case, the server sends back the DHCP Reply with the `L' bit set, and the DHCP Reply is addressed to the agent-address found in the DHCP Request message. ALl the fields in the DHCP Reply message are set by the DHCP server. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-type = 4 |L| status | transaction-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | client's link-local address | | (16 octets, if present) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | extensions (variable number and length) .... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ L If set, the client's link-local address is present Bound, Perkins Expires 25 August 1999 [Page 12]
Internet Draft DHCP Version 6 25 February 1999 status One of the following decimal values: 0 Success 16 Failure, reason unspecified 17 Authentication failed or nonexistent 18 Poorly formed Request or Release 19 Resources unavailable 20 Client record unavailable 21 Invalid client IP address in Release 23 Relay cannot find Server Address 64 Server unreachable (ICMP error) transaction-ID An unsigned integer identifier used to identify this Reply, and copied from the client's Request. client's link-local address If present, the IP address of the client interface which issued the corresponding DHCP Request message. extensions See [15]. If the `L' bit is set, the client's link-local address is present in the Reply message. Then the Reply is sent by the server to the relay's address which was specified as the agent-address in the DHCP Request message, and the relay uses the link-local address to deliver the Reply message to the client. The transaction-ID in the DHCP Reply is copied by the server from the client Request message. 4.5. DHCP Release Message Format The DHCP Release message is sent without the assistance of any DHCP relay. When a client sends a Release message, it is assumed to have a valid IP address with sufficient scope to allow access to the target server. If parameters are specified in the extensions, only those parameters are released. The values of all fields of the DHCP Release message are entered by the Client. The DHCP server acknowledges the Release message by sending a DHCP Reply (Sections 4.4, 6.3). Bound, Perkins Expires 25 August 1999 [Page 13]
Internet Draft DHCP Version 6 25 February 1999 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-type = 1 |D| reserved | transaction-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | client's link-local address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | agent-address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | client-address | | (16 octets, if present) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | extensions (variable number and length) .... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ msg-type 5 D If the `D' flag is set, the client instructs the server to send the DHCP Reply directly back to the client, instead of using the given agent-address and link-local address to relay the Reply message. reserved 0 transaction-ID A unsigned integer identifier used to identify this Release, and copied into the Reply. client's link-local address The IP link-local address of the client interface from which the the client issued the DHCP Release message agent-address The IP address of the agent interface for the IP address to be released. client-address The IP address of the client interface from which the the client issued the DHCP Release message. The client-address field is present whenever the `D' bit is set, even if it is equal to the link-local address. extensions See [15] It is an error (status code ``InvalidSource'' (see Section 2.4)) to include within the DHCP Release message both the `D' bit and an IP Bound, Perkins Expires 25 August 1999 [Page 14]
Internet Draft DHCP Version 6 25 February 1999 address extension which has the IP address used as the client-address field of the DHCP Release message header. 4.6. DHCP Reconfigure Message Format DHCP Reconfigure messages can only be sent to clients which have established an IP address which routes to the link at which they are reachable, hence the DHCP Reconfigure message is sent without the assistance of any DHCP relay. When a server sends a Reconfigure message, the receivers are assumed to have a valid IP address with sufficient scope to be accessible by the server. Only the parameters which are specified in the extensions to the Reconfigure message need be requested again by the client. A Reconfigure message can either be unicast or multicast by the server. The client will extract the extensions provided by the server and send a DHCP Request message to the server using those extensions (see section 5.7). 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-type = 6 |N| reserved | transaction-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | server-address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | extensions (variable number and length) .... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ N The `N' flag indicates that the client should not expect a DHCP Reply in response to the DHCP Request it sends as a result of the DHCP Reconfigure message. reserved 0 transaction-ID A unsigned integer identifier used to identify this Reconfigure, to by copied into the following DHCP Request message that will be transmitted by the client. server-address The IP address of the DHCP server issuing the DHCP Reconfigure message. extensions See [15] Bound, Perkins Expires 25 August 1999 [Page 15]
Internet Draft DHCP Version 6 25 February 1999 5. DHCP Client Considerations A node which is not a DHCP agent MUST silently discard any DHCP Solicit, DHCP Request, or DHCP Release message it receives. 5.1. Verifying Resource Allocations After Restarts A client MAY retain its configured parameters and resources across client system reboots and program restarts. Any client wishing to use this feature MUST also maintain state for the address of its DHCP agent address. When the client restarts, the client MUST also formulate a DHCP Request message to verify that its configured parameters and resources are still valid. This Request message MUST have the `C' bit set, to clean up stale client binding information at the server which may no longer be in use by the client; stale information is that which the client does not include in extensions to such request messages. If the server does not respond to the DHCP Request message after REQUEST_MSG_MIN_RETRANS (see section 8), the client may still use any resources whose lifetimes have not yet expired. In such cases, however, the client MUST begin to search for another server by multicasting a DHCP Solicit message with the `C' bit set (see section 5.2). The client SHOULD log a DHCP System Error. This also handles the case wherein a client restarts on a new network, where its IP address is no longer valid. In this situation, when the client receives a new IP address and the old IP address is no longer needed, the client MUST release its old IP address by issuing a DHCP Release message with the appropriate extension if it can communicate with its previous server. A mobile client (that is not stationary on a network) SHOULD keep its agent-address, and possibly the relevant server address, along with all resource-server associations [15] on non-volatile storage. This will allow the client to release resources with the DHCP Solicit or Release messages if it enters a different network location before releasing its resources. 5.2. Sending DHCP Solicit Messages A client MUST have the address of a server to send a Request message. The client SHOULD locate a DHCP server by multicasting a DHCP Solicit message to the All-DHCP-Agents link-local multicast address (see Section 3.3), setting the Hop Limit == 1. If there are no DHCP servers on the same link as the node, then a DHCP relay MUST be Bound, Perkins Expires 25 August 1999 [Page 16]
Internet Draft DHCP Version 6 25 February 1999 present if solicitations sent from a client's link-local address are to be handled. When sending a DHCP Solicit message, a client MUST set the Relay Address field to 16 octets of zeros, and zero the prefix-size field. If a client reboots and does not have a valid IP address, it SHOULD set the `C' bit in the DHCP Solicit message it sends when restarting. By setting the `C' bit in the solicitation, a client requests that all the DHCP servers that receive the solicitation should clean up their client records that match its link-local address. If a client sends a DHCP Solicit message after it reboots, the solicitation SHOULD be delayed after reception of the first Router Advertisement [14] message (see section 5.8), by at least some random amount of time between MIN_SOLICIT_DELAY and MAX_SOLICIT_DELAY (see section 8). This delay is intended to help stagger requests to DHCP servers (and avoid link-layer collisions) after a power outage causes many nodes to reboot all at once. Each subsequent DHCP Solicit message that is issued before receiving an advertisement MUST be delayed by twice the amount by which the previous DHCP Solicit message was delayed, plus a small random delay between MIN_SOLICIT_DELAY and MAX_SOLICIT_DELAY seconds. 5.3. Receiving DHCP Advertise Messages After a client has received a DHCP Advertise message, it has the address of a server for subsequent DHCP Request messages. If the `S' bit is zero, the DHCP Advertise message was transmitted by a server on the same link as the client, and the client uses the agent-address as the server's address; otherwise, the server's IP address is located in the server-address field. If the server-address is a multicast address, the advertisement MUST be silently discarded. A server MAY append extensions to its advertisements; this might allow the client to select the configuration that best meets its needs from among several prospective servers. Unless a DHCP Advertisement is received with a preference equal to 255 (see Section 4.2), the client MUST wait CLIENT_ADV_WAIT seconds after issuing the DHCP Solicit message in order to receive the Advertisement with the highest preference. After waiting for that period of time, a client MUST select the highest preference server as the target of its DHCP request. If a client receives an advertisement with a preference of 255, it does not have to wait for any more advertisements. Bound, Perkins Expires 25 August 1999 [Page 17]
Internet Draft DHCP Version 6 25 February 1999 If a client sends a DHCP Request to a highly preferred server but fails to receive a DHCP reply from that server after following the retransmission algorithm in section 8, the client MUST then try to send a DHCP Request to a less preferred server. A client is free to cache the result of any DHCP Advertisement it receives. This is purely a potential performance enhancement, because the results might change over time. A client may not get a DHCP Reply if it uses a cached server-address, and in that case SHOULD multicast another DHCP Solicit message. 5.4. Sending DHCP Request Messages A client obtains configuration information from a server by sending a DHCP Request message. The client MUST know the server's address before sending the Request message, and the client MUST have acquired a (possibly identical) DHCP agent address. If the client and server are on the same link, the agent-address used by the client MUST be the same as the DHCP server's address. A DHCP Request message MUST NOT be sent to any multicast address, since otherwise multiple DHCP servers would possibly allocate resources to the client in response to the same Request, and the client would have no way to know which servers had made the allocations, if any packets were lost due to collisions, etc. If the DHCP server is off-link, and the client has no valid IP address of sufficient scope, then the client MUST include the server-address and set the `S' bit in the DHCP Request message. In this case, the IP destination address in the IP header will be a DHCP relay address. Otherwise, if the client has a valid IP address of sufficient scope and knows the IP address of a candidate server, it MUST send the Request message directly to the server without requiring the services of the local DHCP relay. If a client wishes to instruct a server to deallocate all unknown previous resources, configuration information, and bindings associated with its agent-address and link-local address, it sets the `C' bit in the DHCP Request. A client MAY send in such a Request even when it is no longer attached to the link on which the relay-address is attached. The `C' bit allows better reclamation of available resources when a client lost records for its resource-server associations and might not otherwise be able to release the associated resources. When a client reboots and loses its previous state, the server should no longer keep track of the the XID-TIMEOUT binding cache of Bound, Perkins Expires 25 August 1999 [Page 18]
Internet Draft DHCP Version 6 25 February 1999 transaction IDs (see section 6) associated with that previous state. In order to inform the server that the client no longer wishes any association to be maintained between used transaction-IDs and previous transactions, the client SHOULD set the `R' bit in its DHCP Request. In any case, after choosing a transaction-ID which is numerically greater than its last recorded transaction-ID, and filling in the appropriate fields of the DHCP Request message, the client MAY append various DHCP Extensions to the message. These extensions denote specific requests by the client; for example, a client may request a particular IP address, or request that the server send an update containing the client's new IP address to a Domain Name Server. When all desired extensions have been applied, the client sends the DHCP Request to the appropriate agent. For each pending DHCP Request message, a client MUST maintain the following information: - The transaction-ID of the request message, - The server-address, - The agent-address (which can be the same as the server-address), - The time at which the next retransmission will be attempted, and - All extensions appended to the request message. If a client does not receive a DHCP Reply message (Section 5.5) with the same transaction-ID as a pending DHCP Request message within REPLY_MSG_TIMEOUT (see section 8) seconds, or if the received DHCP Reply message contains a DHCP Authentication extension which fails to provide the correct authentication information, the client MUST retransmit the Request with the same transaction-ID and continue to retransmit according to the rules in Section 8. If (after following those rules) the client has not received a Reply message, it SHOULD start over again by multicasting a new DHCP Solicit message to find a different server. If the client receives an ICMP error message in response to such a DHCP Request, it likewise SHOULD start over again by multicasting a new DHCP Solicit message, to find a different server. If the client transmits a DHCP Request in response to a DHCP Reconfigure message, further processing is as specified in Section 5.7. The client can continue to operate with its existing configuration information and resources until it receives the corresponding DHCP Reply from the server. The same retransmission rules apply as for any other DHCP Request message from the client. When the `N' bit is set, a DHCP Request sent in response to a DHCP Reconfigure message will not elicit a DHCP Reply message from the server. Bound, Perkins Expires 25 August 1999 [Page 19]
Internet Draft DHCP Version 6 25 February 1999 5.5. Receiving DHCP Reply Messages When a client receives a DHCP Reply message, it MUST check whether the transaction-ID in the Reply message matches the transaction-ID of a pending DHCP Request message. If no match is found, the Reply message MUST be silently discarded. If the Reply message is acceptable, the client processes each Extension [15], extracting the relevant configuration information and parameters for its network operation. The client can determine when all extensions in the Reply have been processed by using the UDP Length field of the Reply. Some extensions in the Reply may have status codes, which indicate to the client the reason for failure when the server was unable to honor the request. If the server is unable to honor the request in an extension included by the client, that extension may simply be omitted from the Reply. The server MAY also provide the client with configuration parameters the client did not specifically request. Some configuration information extracted from the extensions to the DHCP Reply message MUST remain associated with the server that sent the message. The particular extensions that require this extra measure of association with the server are indicated in the DHCP Extensions document [15]. These "resource-server" associations are used when sending DHCP Release messages. 5.6. Sending DHCP Release Messages If a client wishes to ask the server to release all information and resources relevant to the client, the client SHOULD send a DHCP Release message without any extensions; this is preferable to sending a DHCP Request message with the `C' bit set and no extensions. If a client wishes to retain some of its network configuration parameters, but determines that others are no longer needed, it SHOULD enable the server to release allocated resources which are no longer in use by sending a DHCP Release message to the server, and including extensions to identify the unneeded items. The client consults its list of resource-server associations in order to determine which server should receive the desired Release message. The Release MUST be transmitted to the server that provided the configuration parameters. Suppose a client wishes to release resources which were granted to it at another IP address. Further, suppose that the client has an IP address that will still be valid after the server performs the operations requested in the extensions to the DHCP Release message, and which has sufficient scope to be reachable from the server. In that case, and only then, the client MUST set the `D' bit in the DHCP Bound, Perkins Expires 25 August 1999 [Page 20]
Internet Draft DHCP Version 6 25 February 1999 Release message (see section 4.5). This instructs the server to send the DHCP Reply directly back to the client at the latter valid IP address, instead of performing the default processing of sending the DHCP Reply back through the agent-address included in the DHCP Release. 5.7. Receiving DHCP Reconfigure Messages Each client implementation MUST support listening at UDP port 546 to receive possible DHCP Reconfigure messages; in cases where the client knows that no Reconfigure message will ever be issued, the client MAY be configured to avoid executing this supported feature. Any DHCP Reconfigure message received with a transaction-ID greater than or equal to 1024 MUST be silently discarded. In some cases, the IP address at which the client listens will be a multicast address sent to the client by the server in an extension to an earlier DHCP Reply message. If the client does not listen for DHCP Reconfigure messages, it is possible that the client will not receive notification that its server has deallocated the client's IP address and/or other resources allocated to the client. See discussion in 6.5. The client MAY receive a prefix update for one or more of their addresses and then MUST use that prefix for those addresses. If a client receives a DHCP Reconfigure message, it is a request for the client to send a new DHCP Request to the server which sent the Reconfigure message. Unless the `N' bit is set, the client MUST await a DHCP Reply with a matching transaction-ID, retransmitting (as specified in section 8) until the Reply is received. The server sending the Reconfigure message MAY be different than the server which sent a DHCP Reply message containing the original configuration information. Reconfigure messages MAY be retransmitted by the server with the same transaction-ID. When a client receives a retransmitted unicast Reconfigure message within XID_TIMEOUT of the last received Reconfigure message with the same transaction-ID, the client MUST reformulate exactly the same DHCP Request message and retransmit the request message to the server again. In this way, the server can make use of the retransmission algorithm to ensure that a client has received the Reconfigure message. When a client receives a retransmitted multicast Reconfigure message within XID_TIMEOUT of the last received Reconfigure message with the same transaction-ID, the client MUST not resend the the Request Bound, Perkins Expires 25 August 1999 [Page 21]
Internet Draft DHCP Version 6 25 February 1999 message if RECONF_MULTICAST_REQUEST_WAIT (see section 8) has not expired. If RECONF_MULTICAST_REQUEST_WAIT has expired then the client MUST reformulate exactly the same DHCP Request message and retransmit the Request message to the server again, and then reset RECONF_MULTICAST_REQUEST_WAIT to its default value or the value that was provided from a retransmission extension [15] provided by the server. In this way, the server can make use of the retransmission algorithm to ensure that all affected clients have received the multicast Reconfigure message. For each Extension which is present in the Reconfigure message, the client MUST append a matching Extension to its Request message, which it formulates to send to the server specified in the server-address field of the message. The client also copies a transaction-ID from the Reconfigure message into the Request message. Processing for the Request is the same as specified in Section 5.4, except: - the client retransmits as stated above in this section - the client never needs a Relay to send the Request to the DHCP Server - the client MUST NOT set the `S' or `R' bits - if the `N' Bit is set, the client will not get a Reply from the server - if the client receives an ICMP error message it should abort the Reconfigure transaction and log an error message. The client MUST NOT transmit a DHCP Solicit message in order to rediscover the IP address of the DHCP Server. Resources held by the client which are not identified by Extensions in the server's Reconfigure message are not affected. A server may ask its client to join a multicast group for the purpose of receiving DHCP Reconfigure messages. When a Reconfigure message is delivered to the client by way of the selected multicast address, the client MUST delay its further response for a random amount of time uniformly distributed within the interval between RECONF_MMSG_MIN_RESP and RECONF_MMSG_MAX_RESP seconds (see section 8). This will minimize the likelihood that the server will be flooded with DHCP Request messages. 5.8. Interaction with Stateless Address Autoconfiguration Please refer to the Stateless Address Autoconfiguration Protocol specification [20] for details regarding the actions taken by clients Bound, Perkins Expires 25 August 1999 [Page 22]
Internet Draft DHCP Version 6 25 February 1999 upon receiving Router Advertisements with changing values for the `M' and `O' bits. 6. DHCP Server Considerations A node which is not a client or relay MUST ignore any DHCP Advertise, DHCP Reply, or DHCP Reconfigure message it receives. A server maintains a collection of client records, called ``bindings''. Each binding is uniquely identifiable by the ordered pair <link-local address, agent-address>, since the link-local address is guaranteed to be unique [20] on the link identified by the agent-address and prefix. An implementation MUST support bindings consisting of at least a client's link-local address, agent-address, preferred lifetime and valid lifetime [20] for each client address. A server MAY, at the discretion of the network administrator, be configured so that client bindings are identified by the client's link-local address, without need to use the additional information supplied by the agent-address. A client binding may be used to store any other information, resources, and configuration data which will be associated with the client. A server MUST retain its clients' bindings across server reboots, and, whenever possible, a client should be assigned the same configuration parameters despite server system reboots and DHCP server program restarts. A server MUST support fixed or permanent allocation of configuration parameters to specific clients. In addition to the client binding a server must maintain an XID_TIMEOUT binding cache to determine if a previous transaction-ID is being retransmitted by a client. An implementation of an XID_TIMEOUT binding cache MUST support at least a tuple consisting of the client's link-local address, agent-address prefix, IPv6 address, and XID_TIMEOUT value when the cache entry can be deleted (see Section 8). 6.1. Receiving DHCP Solicit Messages If the DHCP Solicit message was received at the All-DHCP-Servers multicast address, the server MUST check to make sure that the relay-address is present, and is not a link-local address. If the relay-address is not present, or if it is a link-local address, the server MUST silently discard the packet. Note that if the client sends a DHCP Solicit message from a link-local address, the multicast destination will be the All-DHCP-Agents address, not the All-DHCP-Servers address. Bound, Perkins Expires 25 August 1999 [Page 23]
Internet Draft DHCP Version 6 25 February 1999 When the `C' bit is set in the solicitation, the server deallocates all resources that match the link-local address and saved agent-address in the solicitation message, if a binding for the client can be found. If a client binding cannot be found the server SHOULD continue to process the Solicit message. As an optimization, a server processing a Solicit message from relays MAY check the prefix of the IP source address in the IP header to determine whether the server has received the Solicit from multiple relays on the same link. The prefix-size field in the solicitation enables the server to ascertain when two relay addresses belong to the same link. 6.2. Sending DHCP Advertise Messages Upon receiving and verifying the correctness of a DHCP Solicit message, a server constructs a DHCP Advertise message and transmits it on the same link as the solicitation was received from. When the solicitation is received at the All-DHCP-Servers multicast address, the server SHOULD delay the transmission of its advertisement for a random amount of time between SERVER_MIN_ADV_DELAY and SERVER_MAX_ADV_DELAY (see section 8). If the relay-address is nonzero, the server MUST copy it into the agent-address field of the advertisement message, and send the advertisement to the relay-address. Otherwise, the server MUST send the advertisement to the client's link-local address. An IP address of the interface on which the server received the Solicit message MUST appear in the server-address field of the corresponding advertisement, and the 'S' bit MUST be set. The server MAY append extensions to the Advertisement, in order to offer the soliciting node the best possible information about the available services and resources. 6.3. DHCP Request and Reply Message Processing DHCP server MUST check to ensure that the client's link-local address field of the Request message contains a link-local address. If not, the message MUST be silently discarded. If the `S' bit is set, the server MUST check that the server-address matches one of its own IP addresses. If the server-address does not match, the Request message MUST be silently discarded. If the received agent-address and link-local address do not correspond to any binding known to the server, then the server SHOULD create a new binding for the previously unknown client, Bound, Perkins Expires 25 August 1999 [Page 24]
Internet Draft DHCP Version 6 25 February 1999 and send a DHCP Reply with any resources allocated to the new binding. Otherwise, if the server cannot create a new binding, it SHOULD return a DHCP Reply with a status of ``NoBinding'' (see Section 2.4). If the client is updating its resources but the database is temporarily unavailable, the server SHOULD return a DHCP Reply with a status of ``Unavail'' (see Section 2.4). While processing the Request, the server MUST first determine whether or not the Request is a retransmission of an earlier DHCP Request from the same client. This is done by comparing the transaction-ID to all those transaction-IDs in the XID_TIMEOUT binding cache received from the same client during the previous XID_TIMEOUT seconds. If the transaction-ID is the same as one received during that time, the server MUST take the same action (e.g., retransmit the same DHCP Reply to the client) as it did after processing the previous DHCP Request with the same transaction-ID. Otherwise, if the server has no record of a message from the client with the same transaction-ID, the server identifies and allocates all the relevant information, resources, and configuration data that is associated with the client. Then it sends that information to its client by constructing a DHCP Reply message and including the client's information in DHCP Extensions to the Reply message. The DHCP Reply message uses the same transaction-ID as found in the received DHCP Request message. Note that the reply message MAY contain information not specifically requested by the client. If the DHCP Request message has the `S' bit set in the message header, the server MUST send the corresponding DHCP Reply message to the agent-address found in the Request (see section 7.2). Otherwise, the server SHOULD send the corresponding DHCP Reply message to the IP source address in the IP header received from the client Request message. 6.3.1. Processing for Extensions to DHCP Request and Reply Messages The DHCP Request may contain extensions [15], which are interpreted (by default) as advisory information from the client about its configuration preferences. For instance, if the IP Address Extension is present, the server SHOULD attempt to allocate or extend the lifetime of the address indicated by the extension. Some extensions may be marked by the client as required. The server may accept some extensions for successful processing and allocation, while still rejecting others, or it may reject various extensions for different reasons, and set the status appropriately for those extensions which return status to the client. The server Bound, Perkins Expires 25 August 1999 [Page 25]
Internet Draft DHCP Version 6 25 February 1999 sends a single DHCP Reply message in response to each DHCP Request, with the same transaction-ID as the Request. Whenever it is able to, the server includes an extension in the Reply message for every extension sent by the client in the Request message. If the client requests some extensions that cannot be supplied by the server, the server can simply fail to provide them, not including them in the Reply. Other extensions can be rejected by including them in the Reply with an appropriate status indicating failure. The server can include extensions in the reply that were not requested by the client. 6.3.2. Client Requests to Deallocate Unknown Resources When a client DHCP Request is received that has the `C' bit set, the server should check to find out whether the extensions listed in the Request message match those which it has associated with the client's binding. Any resources which are not indicated by the client are presumed to be unknown by the client, and thus possible candidates for reallocation to satisfy requests from other clients. The server MUST deallocate all resources associated with the client upon reception of a DHCP Request with the `C' bit set, except for those which the server is willing to reallocate in response to the client's request. It may be more efficient to avoid deallocating any resources until after the list of extensions to the request has been inspected. 6.4. Receiving DHCP Release Messages If the server receives a DHCP Release Message, it MUST verify that the link-local address field of the message contains an address which could be a valid link-local address (see Section 2.1). If not, the message MUST be silently discarded. In response to a DHCP Release Message with a valid client's link-local address and agent-address, the server formulates a DHCP Reply message that will be sent back to the releasing client. When the `D' flag is set, the server MUST send the DHCP Reply back to the client using the client-address field of the Release message. Otherwise, if the `D' bit is not set, the server MUST send its DHCP Reply message (with the `L' bit set) to the agent-address in the Release message, so that the relay agent can subsequently forward the Reply back to the releasing client at the client's link-local address indicated in the Reply message. If the received agent-address and link-local address do not correspond to any binding known to the server, then the server SHOULD Bound, Perkins Expires 25 August 1999 [Page 26]
Internet Draft DHCP Version 6 25 February 1999 return a DHCP Reply, indicating the error by setting the status code to ``NoBinding'' (see Section 2.4). Otherwise, if the agent-address and link-local address indicate a binding known to the server, then the server continues processing the Release message. If there are any extensions, the server releases the particular configuration items specified in the extensions. If there are no extensions, the server releases all configuration information in the client's binding. After performing the operations indicated in the DHCP Release message and its extensions, the server formulates a DHCP Reply message, copying the transaction-ID from the DHCP Release message. For each Extension in the DHCP Release message successfully processed by the server, a matching Extension is appended to the DHCP Reply message. For extensions in the DHCP Release message which cannot be successfully processed by the server, a DHCP Reply message containing extensions with the appropriate status MUST be returned by the server. If the Release message contains no extensions, the server does not include any extensions in the corresponding DHCP Reply message to the client. 6.5. Sending DHCP Reconfigure Messages If a server needs to change the configuration associated with any of its clients, it constructs a DHCP Reconfigure message (possibly including relevant extensions) and sends it to each such client. The Reconfigure MAY be sent to a multicast address chosen by the server, which was previously sent to each such client in an extension to a previous DHCP Reply message. It may happen that a client does not send a DHCP Request message after the DHCP Reconfigure message has been issued and retransmitted RECONF_MSG_MIN_RETRANS times, according to the algorithm specified in Section 8. This can happen when the client is not listening for the Reconfigure message, possibly because the client is a mobile node disconnected from the network, or because the client node has sustained a power outage or operating system crash. In such cases, the server SHOULD reserve any resources issued to the client until the client responds at some future time, until the resource allocation times out (see section 6.6), or until administrative intervention causes the resources to be manually returned to use. The server SHOULD also log a DHCP System Error. If the server gets another DHCP Request from a client, with a transaction-ID which does not match that of the recently transmitted reconfigure message, the server SHOULD send a DHCP Reply to Bound, Perkins Expires 25 August 1999 [Page 27]
Internet Draft DHCP Version 6 25 February 1999 the client, and wait for RECONF_MSG_RETRANS_INTERVAL, before retransmitting the DHCP Reconfigure again. 6.6. Client-Resource timeouts Some resources (for instance, a client's IP address) may only be allocated to a client for a particular length of time (for instance, the valid lifetime of an IP address). If the client does not renew the resource allocation for such a resource, the server MAY make the resource available for allocation to another client. However, under administrative control, the server MAY reserve any resources issued to the client until the client responds at some future time. 7. DHCP Relay Considerations The DHCP protocol is constructed so that a relay does not have to maintain any state in order to mediate DHCP client/server interactions. The DHCP relay enables clients and servers to carry out DHCP protocol transactions. DHCP Solicit messages are issued by the relay when initiated by prospective clients. By default, the relay locates servers by use of multicasting solicitations to the All-DHCP-Servers multicast group, but relays SHOULD allow this behavior to be configurable. The relay MUST be able to determine which of its interfaces received the client's solicitation message. 7.1. DHCP Solicit and DHCP Advertise Message Processing Upon receiving a DHCP Solicit message from a prospective client, a relay, by default, forwards the message to servers at a site according to the following procedure: - copying the prospective client's solicitation message fields into the appropriate fields of the outgoing solicitation, - copying a non-link-local address of its interface from which the solicitation was received from the client into the relay-address field, and - setting the prefix-size field appropriately, - by default, setting the hop-count field in the IP header of the solicitation to the value DEFAULT_SOLICIT_HOPCOUNT (see section 8). Bound, Perkins Expires 25 August 1999 [Page 28]
Internet Draft DHCP Version 6 25 February 1999 - setting the IP source address to be a site-local or global-scope address belonging to the relay's interface on which the client's original solicitation was received, - finally, sending the resulting message to one or more servers. By default, the relay sends solicitations to the All-DHCP-Servers multicast address, FF05:0:0:0:0:0:1:3. However, the relay MAY be configured with an alternate server address, or the FQDN of a server. Methods for automatically updating such alternately configured server addresses are not specified in this document. When the relay receives a DHCP advertisement, it relays the advertisement to the client at the client's link-local address by way of the interface indicated in the agent's address field. 7.2. DHCP Request Message Processing When a relay receives a DHCP Request message, it SHOULD check that the IP source address in the IP header is a link-local address, that the link-local address matches the link-local address field in the Request message header, and that the agent-address field of the message matches an IP address associated with the interface from which the DHCP Request message was received. If any of these checks fail, the relay MUST silently discard the Request message. The relay MUST check whether the `S' bit is set in the message header. If not, the packet is discarded, and the relay SHOULD return a DHCP Reply message to the address contained in the client's link-local address field of the Request message, with status ``PoorlyFormed'' (see Section 2.4). If the received request message is acceptable, the relay then transmits the DHCP Request message to the address of the server found in the server-address field of the received DHCP Request message. All of the fields of DHCP Request message transmitted by the relay are copied over unchanged from the DHCP Request received from the client. Only the fields in the IP header will differ from the packet received from the client. All relays MUST send DHCP Request messages using the source IP address from the interface where the DHCP request was received. If the Relay receives an ICMP error, the Relay SHOULD return a DHCP Reply message to the client address (which can be found in the payload of the ICMP message [5]), with status ``ICMPError'' (see Section 2.4), along with the DHCP Relay ICMP Error extension [15]. Bound, Perkins Expires 25 August 1999 [Page 29]
Internet Draft DHCP Version 6 25 February 1999 7.3. DHCP Reply Message Processing When the relay receives a DHCP Reply, it MUST check that the message has the `L' bit set. It MUST check that the client's link-local address field contains a link-local address. If either check fails, the packet MUST be silently discarded. If both checks are satisfied, the relay MUST send a DHCP Reply message to the link-local address listed in the received Reply message. Only the fields in the IP header will differ from the packet received from the server, not the payload. 8. Retransmission and Configuration Variables When a client does not receive a DHCP Reply in response to a pending DHCP Request, the client MUST retransmit the identical DHCP Request, with the same transaction-ID, to the same server again until it can be reasonably sure that the server is unavailable and an alternative can be chosen. The DHCP server assumes that the client has received the configuration information included with the extensions to the DHCP Reply message, and it is up to the client to continue to try for a reasonable amount of time to complete the transaction. All the actions specified for DHCP Request in this section hold also for DHCP Release messages sent by the client. Similarly, when a client sends a DHCP Request message in response to a Reconfigure message from the server, the client assumes that the DHCP server has received the Request. The server MUST retransmit the identical DHCP Reconfigure to the client a reasonable number of times to try to elicit the Request message from the client. If no corresponding DHCP Request is received by the server after REQUEST_MSG_MIN_RETRANS retransmissions, the server MAY erase or deallocate information as needed from the client's binding, but see section 6.5. Retransmissions occur using the following configuration variables for a DHCP implementation. These configuration variables MUST be configurable by a client or server: CLIENT_ADV_WAIT The minimum amount of time a client waits to receive DHCP Advertisements after transmitting a DHCP Solicit to the All-DHCP Agents multicast address (see section 5.3). Default: 2 seconds Bound, Perkins Expires 25 August 1999 [Page 30]
Internet Draft DHCP Version 6 25 February 1999 DEFAULT_SOLICIT_HOPCOUNT The default hop-count used in the IP header by DHCP relays when sending DHCP Solicit messages on behalf of a client. Default: 4 SERVER_MIN_ADV_DELAY The minimum amount of time a server waits to transmit a DHCP Advertisement after receiving a DHCP Solicit at the All-DHCP-Servers or All-DHCP-Agents multicast address. Default: 100 milliseconds SERVER_MAX_ADV_DELAY The maximum amount of time a server waits to transmit a DHCP Advertisement after receiving a DHCP Solicit at the All-DHCP Agents multicast address. Default: 1 second REPLY_MSG_TIMEOUT The time in seconds that a client waits to receive a server's DHCP Reply before retransmitting a DHCP Request. The client MUST multiply REPLY_MSG_TIMEOUT by a factor of 2 in an exponential manner for each time it retransmits until REQUEST_MSG_MIN_RETRANS (below) is attained. A client MAY be configured to attempt 2 retransmissions before beginning the exponential backoff retransmission in the previous sentence. Default: 2 seconds. REQUEST_MSG_MIN_RETRANS The minimum number of DHCP Request transmissions that a client should retransmit, before aborting the request. Default: 10 retransmissions. RECONF_MSG_MIN_RETRANS The minimum number of DHCP Reconfigure messages that a server should retransmit, before assuming the the client is unavailable. Default: 10 retransmissions. Bound, Perkins Expires 25 August 1999 [Page 31]
Internet Draft DHCP Version 6 25 February 1999 RECONF_MSG_RETRANS_INTERVAL The least time in seconds that a server waits for a client's DHCP Request before each retransmission of the DHCP Reconfigure. Default: 12 seconds. RECONF_MMSG_MIN_RESP The minimum amount of time before a client can respond to a DHCP Reconfigure message sent to a multicast address. Default: 2 seconds. RECONF_MMSG_MAX_RESP The maximum amount of time before a client MUST respond to a DHCP Reconfigure message sent to a multicast address. Default: 10 seconds. RECONF_MULTICAST_REQUEST_WAIT The time a client should wait before retransmitting a Request message in reponse to a retransmitted multicast Reconfigure message. Default: 120 seconds MIN_SOLICIT_DELAY The minimum amount of time a prospective client is required to wait, after determining from a Router Advertisement message that the client should perform stateful address configuration, before sending a DHCP Solicit to a server. Default: 1 second MAX_SOLICIT_DELAY The maximum amount of time a prospective client is required to wait, after determining from a Router Advertisement message that the client should perform stateful address configuration, before sending a DHCP Solicit to a server. Default: 5 seconds Bound, Perkins Expires 25 August 1999 [Page 32]
Internet Draft DHCP Version 6 25 February 1999 XID_TIMEOUT The amount of time a DHCP server has to keep track of client transaction-IDs in order to make sure that client retransmissions using the same transaction-ID are idempotent. Default: 600 seconds 9. Security Considerations Clients and servers often have to authenticate the messages they exchange. For instance, a server may wish to be certain that a DHCP Request originated from the client identified by the <link-local address, agent-address> fields included within the Request message header. Conversely, it is quite often essential for a client to be certain that the configuration parameters and addresses it has received were sent to it by an authoritative server. Similarly, a server should only accept a DHCP Release message which seems to be from one of its clients, if it has some assurance that the client actually did transmit the Release message. Again, a client might wish to only accept DHCP Reconfigure messages that are certain to have originated from a server with authority to issue them. The IPv6 Authentication Header can provide security for DHCPv6 messages when both endpoints have a suitable IP address. However, a client often has only a link-local address, and such an address is not sufficient for a server which is off-link. In those circumstances the DHCP relay is involved, so that the DHCP message MUST have the relay's address in the IP destination address field, even though the client aims to deliver the message to the server. The DHCP Client-Server Authentication Extension [15] is intended to be used in these circumstances. Note that, if a client receives a DHCP message which fails authentication, it should continue to wait for another message which might be correctly authenticated just as if the failed message had never arrived; however, receiving such failed messages SHOULD be logged. 10. Year 2000 considerations Since all times are relative to the current time of the transaction, there is no problem within the DHCPv6 protocol related to any hardcoded dates or two-digit representation of the current year. Bound, Perkins Expires 25 August 1999 [Page 33]
Internet Draft DHCP Version 6 25 February 1999 11. IANA Considerations This document defines message types 1-7 to be received by UDP at port numbers 546 and 547. Additional message types may be defined in the future. Section 3.3 specifies the use of several multicast groups, with multicast addresses FF02:0:0:0:0:0:1:2, FF05:0:0:0:0:0:1:3, and FF05:0:0:0:0:0:1:4. This document also defines several status codes that are to be returned with the DHCP Reply message (see section 4.4). The nonzero values for these status codes which are currently specified are shown in section 2.4. There is a DHCPv6 extension [15] which allows clients and servers to exchange values for some of the timing and retransmission parameters defines in section 8. Adding new parameters in the future would require extending the values by which the parameters are indicated in the DHCP extension. Since there needs to be a list kept, the default values for each parameter should also be stored as part of the list. All of these protocol elements may be specified to assume new values at some point in the future. New values should be approved by the process of IETF Consensus [12]. 12. Acknowledgements Thanks to the DHC Working Group for their time and input into the specification. Ralph Droms and Thomas Narten have had a major role in shaping the continued improvement of the protocol by their careful reviews. Many thanks to Matt Crawford, Erik Nordmark, Gerald Maguire, and Mike Carney for their studied review as part of the Last Call process. Thanks also for the consistent input, ideas, and review by (in alphabetical order) Brian Carpenter, Jack McCann, Yakov Rekhter, Matt Thomas, Sue Thomson, and Phil Wells. Thanks to Steve Deering and Bob Hinden, who have consistently taken the time to discuss the more complex parts of the IPv6 specifications. A. Changes for this revision - Fixed grammatical and clarity problems. - Added saved agent-address field to the solicit message and altered and enhanced references to the C bit use. Bound, Perkins Expires 25 August 1999 [Page 34]
Internet Draft DHCP Version 6 25 February 1999 - Removed all references of agent-address prefix as it is implied by the agent-address and can be used as such by implementors. - Verified all binding dependencies use the link-local address and agent-address. - Added clients in what cases SHOULD retain specific addresses when the client is not stationary. - Updated DHCP terminology section and re-ordered. - Put RFC 2119 terms in lower case, in section 3.1. - Changed definition of transaction-ID and specified ranges for client and server use. - Added and fixed text to clarify use of Reconfigure message for clients in all relevant sections. - Added words in spec to differentiate format section from processing section. - Added retransmission algorithm for Reconfigure multicast messages and new configuration parameter. - Differentiated processing for requests by clients when received from Reconfigure message. - Added more words when binding cache is used for XID timeout. - Added exponential backoff to client retransmissions. - Updated the references section. B. Related Protocol Specifications Related work in IPv6 that would best serve an implementor to study is the IPv6 Specification [7], the IPv6 Addressing Architecture [9], IPv6 Stateless Address Autoconfiguration [20], IPv6 Neighbor Discovery Processing [14], and Dynamic Updates to DNS [22]. These specifications enable DHCP to build upon the IPv6 work to provide both robust stateful autoconfiguration and autoregistration of DNS Host Names. The IPv6 Specification provides the base architecture and design of IPv6. A key point for DHCP implementors to understand is that IPv6 requires that every link in the internet have an MTU of 1500 octets or greater (in IPv4 the requirement is 68 octets). This means that Bound, Perkins Expires 25 August 1999 [Page 35]
Internet Draft DHCP Version 6 25 February 1999 a UDP packet of 536 octets will always pass through an internet (less 40 octets for the IPv6 header), as long as there are no IP options prior to the UDP header in the packet. But, IPv6 does not support fragmentation at routers, so that fragmentation takes place end-to-end between hosts. If a DHCP implementation needs to send a packet greater than 1500 octets it can either fragment the UDP packet into fragments of 1500 octets or less, or use Path MTU Discovery [11] to determine the size of the packet that will traverse a network path. It is implementation dependent how this is accomplished in DHCP. Path MTU Discovery for IPv6 is supported for both UDP and TCP and can cause end-to-end fragmentation when the PMTU changes for a destination. The IPv6 Addressing Architecture specification [9] defines the address scope that can be used in an IPv6 implementation, and the various configuration architecture guidelines for network designers of the IPv6 address space. Two advantages of IPv6 are that support for multicast is required, and nodes can create link-local addresses during initialization. This means that a client can immediately use its link-local address and a well-known multicast address to begin communications to discover neighbors on the link. For instance, a client can send a DHCP Solicit and locate a server or relay. IPv6 Stateless Address Autoconfiguration [20] (Addrconf) specifies procedures by which a node may autoconfigure addresses based on router advertisements [14], and the use of a valid lifetime to support renumbering of addresses on the Internet. In addition the protocol interaction by which a node begins stateless or stateful autoconfiguration is specified. DHCP is one vehicle to perform stateful autoconfiguration. Compatibility with Addrconf is a design requirement of DHCP (see Section 3.1). IPv6 Neighbor Discovery [14] is the node discovery protocol in IPv6 which replaces and enhances functions of ARP [16]. To understand IPv6 and Addrconf it is strongly recommended that implementors understand IPv6 Neighbor Discovery. Dynamic Updates to DNS [22] is a specification that supports the dynamic update of DNS records for both IPv4 and IPv6. DHCP can use the dynamic updates to DNS to integrate addresses and name space to not only support autoconfiguration, but also autoregistration in IPv6. The security model to be used with DHCPv6 should conform as closely as possible to the authentication model outlined in [10]. Bound, Perkins Expires 25 August 1999 [Page 36]
Internet Draft DHCP Version 6 25 February 1999 C. Comparison between DHCPv4 and DHCPv6 This appendix is provided for readers who will find it useful to see a model and architecture comparison between DHCPv4 [8, 1] and DHCPv6. There are three key reasons for the differences: o IPv6 inherently supports a new model and architecture for communications and autoconfiguration of addresses. o DHCPv6 benefits from the new IPv6 features. o New features were added to support the expected evolution and the existence of more complicated Internet network service requirements. IPv6 Architecture/Model Changes: o The link-local address permits a node to have an address immediately when the node boots, which means all clients have a source IP address at all times to locate a server or relay agent on the local link. o The need for BOOTP compatibility and broadcast flags is removed. o Multicast and address scoping in IPv6 permit the design of discovery packets that would inherently define their range by the multicast address for the function required. o Stateful autoconfiguration has to coexist and integrate with stateless autoconfiguration supporting Duplicate Address Detection and the two IPv6 lifetimes, to facilitate the dynamic renumbering of addresses and the management of those addresses. o Multiple addresses per interface are inherently supported in IPv6. o Many DHCPv4 options are unnecessary now because the configuration parameters are either obtained through IPv6 Neighbor Discovery or the Service Location protocol [21]. DHCPv6 Architecture/Model Changes: o The message type is the first byte in the packet. o IPv6 Address allocations are now handled in a message extension as opposed to the message header. o Client/Server bindings are now mandatory and take advantage of the client's link-local address to always permit communications Bound, Perkins Expires 25 August 1999 [Page 37]
Internet Draft DHCP Version 6 25 February 1999 either directly from an on-link server, or from a remote server through an on-link relay-agent. o Servers are discovered by a client solicit, followed by a server or relay-agent advertisement. o The client will know if the server is on-link or off-link. o The on-link relay-agent locates remote server addresses from system configuration or by the use of a site wide multicast packet. o ACKs and NAKs are not used. o The server assumes the client receives its responses unless it receives a retransmission of the same client request. This permits recovery in the case where the network has faulted. o Clients can issue multiple, unrelated DHCP Request messages to the same or different servers. o The function of DHCPINFORM is inherent in the new packet design; a client can request configuration parameters other than IPv6 addresses in the optional extension headers. o Clients MUST listen to their UDP port for the new Reconfigure message from servers. o New extensions have been defined. With the changes just enumerated, we can support new user features, including o Configuration of Dynamic Updates to DNS o Address deprecation, for dynamic renumbering. o Relays can be preconfigured with server addresses, or use of multicast. o Authentication o Clients can ask for multiple IP addresses. o Addresses allocated with too-long lifetimes can be reclaimed using the Reconfigure message. o Integration between stateless and stateful address autoconfiguration. Bound, Perkins Expires 25 August 1999 [Page 38]
Internet Draft DHCP Version 6 25 February 1999 o Enabling relay-agents to locate remote servers for a link. D. Full Copyright Statement Copyright (C) The Internet Society (1998). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. References [1] S. Alexander and R. Droms. DHCP Options and BOOTP Vendor Extensions. RFC 2132, March 1997. [2] S. Bradner. Key Words for Use in RFCs to Indicate Requirement Levels. RFC 2119, March 1997. [3] S. Bradner and A. Mankin. The Recommendation for the IP Next Generation Protocol. RFC 1752, January 1995. [4] A. Conta and S. Deering. Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6). RFC 1885, December 1995. [5] A. Conta and S. Deering. RFC 2463: Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Bound, Perkins Expires 25 August 1999 [Page 39]
Internet Draft DHCP Version 6 25 February 1999 Specification, December 1998. Obsoletes RFC1885 [4]. Status: DRAFT STANDARD. [6] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6) Specification. RFC 1883, December 1995. [7] S. Deering and R. Hinden. RFC 2460: Internet Protocol, Version 6 (IPv6) specification, December 1998. Obsoletes RFC1883 [6]. Status: DRAFT STANDARD. [8] R. Droms. Dynamic Host Configuration Protocol. RFC 2131, March 1997. [9] R. Hinden and S. Deering. IP Version 6 Addressing Architecture. RFC 2373, July 1998. [10] S. Kent and R. Atkinson. RFC 2402: IP authentication header, November 1998. Status: PROPOSED STANDARD. [11] J. McCann, S. Deering, and J. Mogul. Path MTU Discovery for IP version 6. RFC 1981, August 1996. [12] T. Narten and H. Alvestrand. RFC 2434: Guidelines for writing an IANA considerations section in RFCs, October 1998. Status: BEST CURRENT PRACTICE. [13] T. Narten, E. Nordmark, and W. Simpson. Neighbor Discovery for IP version 6 (IPv6). RFC 1970, August 1996. [14] T. Narten, E. Nordmark, and W. Simpson. RFC 2461: Neighbor discovery for IP Version 6 (IPv6), December 1998. Obsoletes RFC1970 [13]. Status: DRAFT STANDARD. [15] C. Perkins. Extensions for the Dynamic Host Configuration Protocol for IPv6. draft-ietf-dhc-dhcpv6ext-11.txt, February 1999. (work in progress). [16] David C. Plummer. An Ethernet Address Resolution Protocol: Or Converting Network Protocol Addresses to 48.bit Ethernet Addresses for Transmission on Ethernet Hardware. RFC 826, November 1982. [17] J. B. Postel. User Datagram Protocol. RFC 768, August 1980. [18] J. B. Postel, Editor. Internet Protocol. RFC 791, September 1981. [19] S. Thomson and T. Narten. IPv6 Stateless Address Autoconfiguration. RFC 1971, August 1996. Bound, Perkins Expires 25 August 1999 [Page 40]
Internet Draft DHCP Version 6 25 February 1999 [20] S. Thomson and T. Narten. RFC 2462: IPv6 stateless address autoconfiguration, December 1998. Obsoletes RFC1971 [19]. Status: DRAFT STANDARD. [21] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service Location Protocol. RFC 2165, July 1997. [22] P. Vixie, S. Thomson, Y. Rekhter, and J. Bound. Dynamic Updates in the Domain Name System (DNS). RFC 2136, April 1997. Chair's Address The working group can be contacted via the current chair: Ralph Droms Computer Science Department 323 Dana Engineering Bucknell University Lewisburg, PA 17837 Phone: (717) 524-1145 E-mail: droms@bucknell.edu Author's Address Questions about this memo can be directed to: Jim Bound Charles E. Perkins Compaq Computer Corporation Sun Microsystems Laboratories 110 Spitbrook Road, ZKO3-3/U14 15 Network Circle Nashua, NH 03062 Menlo Park, CA 94025 USA USA Phone: +1-603-884-0400 Phone: +1 650 786-6464 EMail: bound@zk3.dec.com EMail: cperkins@eng.sun.com Fax: +1 650 786-6445 Bound, Perkins Expires 25 August 1999 [Page 41]
