Internet Engineering Task Force C. Perkins INTERNET DRAFT Sun Microsystems 13 March 1998 Extensions for the Dynamic Host Configuration Protocol for IPv6 draft-ietf-dhc-v6exts-09.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. 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.'' To view the entire list of current Internet-Drafts, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this memo is unlimited. Abstract The Dynamic Host Configuration Protocol for IPv6 [4] (DHCPv6) provides a framework for passing configuration information to hosts on a TCP/IP network. Configuration parameters and other control information are carried in typed data items that are stored in the "extensions" field of the DHCPv6 message. The data items themselves are also called "extensions." This document specifies the current set of DHCPv6 extensions. This document will be periodically updated as new extensions are defined. Each superseding document will include the entire current list of Perkins Expires 13 September 1998 [Page i] Internet Draft DHCPv6 Extensions 13 March 1998 valid extensions. The method for specifying new extensions is also included in this document. Perkins Expires 13 September 1998 [Page ii] Internet Draft DHCPv6 Extensions 13 March 1998 Contents Status of This Memo i Abstract i 1. Introduction 1 2. DHCPv6 Extension Field Format 2 2.1. Character Encoding and String Issues . . . . . . . . . . 2 2.2. Typed Scope Lists . . . . . . . . . . . . . . . . . . . . 3 3. IP Address Extension 4 3.1. Client Considerations for the IP Address extension . . . 7 3.1.1. Address Lifetimes . . . . . . . . . . . . . . . . 7 3.1.2. Use with the DHCP Request message . . . . . . . . 8 3.1.3. Receiving as part of the DHCP Reply message . . . 9 3.1.4. Use with the DHCP Release message . . . . . . . . 10 3.2. Server Considerations for the IP Address extension . . . 10 3.2.1. Use with the DHCP Advertise message . . . . . . . 10 3.2.2. Receiving a DHCP Request with the IP Address Extension . . . . . . . . . . . . . . . . 10 3.2.3. Use with the DHCP Reply message . . . . . . . . . 11 3.2.4. Use with the DHCP Reconfigure message . . . . . . 12 3.2.5. Receiving a DHCP Release with the IP Address Extension . . . . . . . . . . . . . . . . 12 3.3. DHCP Relay Considerations . . . . . . . . . . . . . . . . 12 4. General Extensions 12 4.1. Time Offset . . . . . . . . . . . . . . . . . . . . . . . 13 4.2. IEEE 1003.1 POSIX Timezone extension . . . . . . . . . . 13 4.2.1. IEEE 1003.1 POSIX Timezone specifier . . . . . . 13 4.2.2. An Example . . . . . . . . . . . . . . . . . . . 15 4.2.3. Timezone Extension Precedence . . . . . . . . . . 15 4.3. Domain Name Server Extension . . . . . . . . . . . . . . 15 4.4. Domain Name . . . . . . . . . . . . . . . . . . . . . . . 16 5. Application and Service Parameters 16 5.1. Directory Agent Extension . . . . . . . . . . . . . . . . 16 5.2. Service Scope Extension . . . . . . . . . . . . . . . . . 18 5.3. Network Time Protocol Servers Extension . . . . . . . . . 19 5.4. Network Information Service Domain Extension . . . . . . 19 5.5. Network Information Servers Extension . . . . . . . . . . 20 5.6. Network Information Service+ Domain Extension . . . . . . 20 5.7. Network Information Service+ Servers Extension . . . . . 20 Perkins Expires 13 September 1998 [Page iii] Internet Draft DHCPv6 Extensions 13 March 1998 6. TCP Parameters 21 6.1. TCP Keepalive Interval Extension . . . . . . . . . . . . 21 7. DHCPv6 Extensions 21 7.1. Maximum DHCPv6 Message Size Extension . . . . . . . . . . 21 7.2. Platform Specific Information . . . . . . . . . . . . . . 22 7.3. Platform Class Identifier . . . . . . . . . . . . . . . . 23 7.4. Class Identifier . . . . . . . . . . . . . . . . . . . . 24 7.5. Reconfigure Multicast Address . . . . . . . . . . . . . . 25 7.6. Renumber DHCPv6 Server Address . . . . . . . . . . . . . 25 7.7. DHCP Relay ICMP Error Message Format . . . . . . . . . . 25 7.7.1. ICMP Extension Client Considerations . . . . . . 26 7.7.2. ICMP Extension Relay Considerations . . . . . . . 26 7.8. Client-Server Authentication Extension . . . . . . . . . 26 7.9. Client Key Selection Extension . . . . . . . . . . . . . 27 8. End extension specification 28 9. Security Considerations 28 9.1. Replay Protection . . . . . . . . . . . . . . . . . . . . 29 9.2. Default Authentication Algorithm . . . . . . . . . . . . 29 10. Defining New Extensions 29 11. Acknowledgements 31 Chair's Address 33 Author's Address 33 Perkins Expires 13 September 1998 [Page iv] Internet Draft DHCPv6 Extensions 13 March 1998 1. Introduction This document specifies extensions for use with the Dynamic Host Configuration Protocol for IP version 6, DHVPv6. The full description of DHCPv6 message formats may be found in the DHCPv6 specification document [4]. In this document, several words are used to signify the requirements of the specification, in accordance with RFC 2119 [5]. These words (MUST, SHOULD, MAY, MUST NOT, etc) are often capitalized. This document defines the format of information in the last field of DHCPv6 messages ('extensions'). The extensions defined within this document specify a generalized use of this area for giving information useful to a wide class of machines, operating systems and configurations. Sites with a single DHCPv6 server that is shared among heterogeneous clients may choose to define other, site- specific formats for the use of the 'extensions' field. Section 2 of this memo describes the formats of DHCPv6 extensions. Information on registering new extensions is contained in section 10. The other sections organize the format descriptions of various extensions according to their general type, as follows: - IP Address extension - Miscellaneous host configuration - Service Location configuration - Miscellaneous network layer - TCP - Vendor Specific - DHCPv6 Future applications will make extensive use of an ever-increasing number and variety of network services. It is expected that client needs for creating connections with these future network services will be satisfied by the Service Location Protocol [24], and not DHCPv6. DHCP is expected to be used for the kinds of configuration that enable clients to become fully functional as self-contained network entities, but not the kinds of configuration that might be required by applications running above the network or transport layer protocol levels. Perkins Expires 13 September 1998 [Page 1] Internet Draft DHCPv6 Extensions 13 March 1998 2. DHCPv6 Extension Field Format Extensions may be fixed length or variable length. All extensions begin with a type field, which is two octets long and uniquely identifies the extension. Fixed length extensions without data consist of only the two octet type field. Only extension 65535 is fixed length. All other extensions are variable length with a two octet unsigned integer Length field following the type octets. The value of the Length field does not include the four octets specifying the type and length. The Length field is followed by "length" octets of data. In the case of some extensions the length field is a constant but MUST still be specified. In each case, unless otherwise specified, the length field specifies the length of the extension in octets. Any extensions defined subsequent to this document should contain a Length field even if the length is fixed or zero. There is no particular requirement for alignment of the data fields within existing DHCPv6 extensions. Unrecognized extensions SHOULD be skipped by ignoring the number of octets specified in the length field, and processing continued for subsequent extensions. Unless and until specified otherwise by use of extension type 64 (see section 7.1), DHCP entities MUST assume that that the maximum DHCP message size including extensions is 1500 octets. All multi-octet quantities are in network byte-order. Extension types 32768 to 65534 (decimal) are reserved for site-specific extensions. All of the extensions described in this document will also have their default values specified, if any. Whenever an extension is received as part of a DHCP message, any reserved fields of the message MUST be ignored, and processing continued as if the reserved fields were zero. 2.1. Character Encoding and String Issues Certain extensions (e.g., type 16 described in section 5.1) have fields which can use various character encodings. Values for character encoding can be found in the Internet Assigned Numbers Authority's (IANA) database http://www.isi.edu/in-notes/iana/assignments/character-sets and have the values referred by the MIBEnum value. Note that in some character sets, each character may require two or more octets of data for its representation. Perkins Expires 13 September 1998 [Page 2] Internet Draft DHCPv6 Extensions 13 March 1998 The encoding will determine the interpretation of all character data in the corresponding fields of particular extensions. There is no way to mix US-ASCII and UNICODE, for example. All responses MUST be in the character set of the request or use US-ASCII. If a request is sent to a DHCP server, which is unable to manipulate or store the character set of the incoming message, the request will fail. The server returns a status code of 24 in a DHCP Reply message in this case. Requests using US-ASCII (MIBEnum value == 3) will never fail for this reason, since all DHCP entities MUST be able to accept this character set. All DNS-related strings are presumed to be encoded in US-ASCII. 2.2. Typed Scope Lists In Service Location Protocol, multiple service types can be hosted on the same network node. However, DHCP typically configures computers based on their IP address. It is possible that different service types on the same computer would be administered from different scopes. Thus, extensions 16 and 17 have additional syntax to allow this more detailed style of service configuration. In particular, the list of scopes contained in the extensions is syntactically separated into lists pertaining to each service type. Grammatically, a typed-scope-list in a DHCPOFFER is structured as follows: typed-scope-list = one or more maybe-typed-scope-items, separated by commas maybe-typed-scope-item = typed-scope-item, or scope-list typed-scope-item = '(' service-type '=' scope-list ')' scope-list = one or more scope-items, comma-separated A typed-scope-list in a DHCPREQUEST is structured as follows: typed-scope-list = one or more maybe-typed-scope-items, separated by commas maybe-typed-scope-item = typed-scope-item, or maybe-empty-scope-list typed-scope-item = '(' service-type '=' maybe-empty-scope-list ')' maybe-empty-scope-list = zero or more scope-items, comma-separated A service type has the format defined in [10], and a scope-item has the format defined in [11] for "strval". Basically, a scope-item is a character string that has alphanumeric characters not including control characters or `(',`)',`,', \',`!',`<',`=',`>', or `~' Service schemes are special cases of schemes as defined for general URLs [3]. Perkins Expires 13 September 1998 [Page 3] Internet Draft DHCPv6 Extensions 13 March 1998 The typed-scope-list MAY contain both untyped-scope-lists and typed-scope-lists. Each scope-item in each untyped-scope-list applies to every service type on the node. As an example, the scope-list ``A,B,C'' denotes scopes A, B and C for all service types on the client. In a DHCPREQUEST, this scope string would indicate that the client wishes a directory agent which supports ANY of these three scopes. In a DHCPOFFER, the scope indicates that the directory agent supports ALL of the three scopes. Suppose instead that service types "netman" and "proxystuff" are residing on a DHCP client. Then, the typed-scope-list in a DHCPOFFER could be, (netman=mgmt),(proxystuff=math-dept,labs) Assuming the DHCP client with two service types "netman" and "proxystuff" did not make any scope restriction, a corresponding typed-scope-list in a DHCPREQUEST could be, (netman=),(proxystuff=) asking for scopes for those service types. 3. IP Address Extension The IP Address extension is the most essential of all the DHCPv6 extensions. It can be used by both client and server in various ways. Since the IP Address extension can be used more than once in the same DHCP message, all information relevant to a particular IPv6 allocation has to be collected together in the same extension. Some of the fields within the IP Address extension can specify how DNS may be updated [25]. To ask for an IP address in a DHCP Request message, a client includes an IP Address Extension. To renew or extend the lifetime of a particular IP address, the client puts that address in the client address field. To request the allocation of a new but unspecified IP address, the client omits the client address field. The IP address returned by the server in the latter case will be compatible with a routing prefix of the link to which the client is currently attached. An IP Address Extension can contain at most one IP address. To specify more than one IP address, multiple extensions are used. Perkins Expires 13 September 1998 [Page 4] Internet Draft DHCPv6 Extensions 13 March 1998 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | status |C|L|Q|A|P| reserved | pfx-size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (if present) | | client address (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (if present) preferred lifetime (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (if present) valid lifetime (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (if present) DNS name (variable length) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 1 Length (unsigned integer, variable) The length of the Extension in octets. status If the server is unable to honor the client's request, the reason is indicated in the status. C If the 'C' bit is set, the field containing the IP address for the client is present in the extension. L If the 'L' bit is set, the preferred and valid lifetimes are present in the extension. Q If the 'Q' bit is set, the fields included by the client are required, and must be made available by the server or else the extension must be rejected. A If the 'A' bit is set, the client requests that that the the server updates DNS with a new AAAA record, as specified by the client's FQDN. P If the 'P' bit is set, the client requests that that the the server updates DNS with a new PTR record, as specified by the client's FQDN. reserved MUST be zero. pfx-size If the client address is present (the 'C' bit is set), a nonzero pfx-size is the number of leftmost bits of the Perkins Expires 13 September 1998 [Page 5] Internet Draft DHCPv6 Extensions 13 March 1998 client's IPv6 address which make up the routing prefix. Otherwise, if the 'C' bit is not set, pfx-size MUST be zero. client address The IP address to be allocated by the server for use by the client (16 octets long). preferred lifetime The preferred lifetime of the IP address in seconds valid lifetime The valid lifetime of the IP address in seconds DNS name The DNS name (a string of ASCII octets) to be used by the client (variable length). The following values for the status field are defined within this document: 0 request granted, no errors 18 Security parameters failed for this client 20 Resource AAAA Record Parameter Problem 21 Resource PTR Record Parameter Problem 22 Unable to honor required extension parameters 23 DNS name string error 24 dynDNS Not Implemented 25 Authoritative DNS Server could not be found 33 The name server was unable to interpret the request due to a format error. 34 dynDNS Not Available at this time (SERVFAIL) 35 Some name that ought to exist, does not exist (NXDOMAIN) 36 The name server does not support the specified Opcode (NOTIMP) 37 The name server refuses to perform the specified operation for policy or security reasons (REFUSED) 38 Some name that ought not to exist, does exist (YXDOMAIN) 39 Some RRset that ought not to exist, does exist (YXRRSET) 40 Some RRset that ought to exist, does not exist (NXRRSET) 41 The server is not authoritative for the zone named in the Zone Section (NOTAUTH) 42 A name used in the Prerequisite or Update Section is not within the zone denoted by the Zone Section (NOTZONE) Perkins Expires 13 September 1998 [Page 6] Internet Draft DHCPv6 Extensions 13 March 1998 Status values 33 through 42 are described more fully within RFC 2136 [25]. Up-to-date values for the values of the status field are specified in the most recent "Assigned Numbers" [20]. To inform the client of the DYNDNS [25] error return codes (i.e., nonzero return codes) received by the DHCPv6 server the client MUST assume the status codes 32 through 42 are formed as follows: status code = 32 + DYNDNS Error Code The DNS name can be a host name, which does not contain the '.' ASCII character as a separator between DNS hierarchy components. Any name containing the '.' is treated as a Fully Qualified Domain Name (FQDN). The length of the DNS name may be determined by subtracting, from the Length, the length of those fixed length fields which are present. If the 'Q' bit is set, the values or actions requested by the C, L, A, and P bits are required, and MUST be provided, or the extension MUST be rejected with status code 22. If the 'Q' bit is set, and if the 'A' bit is set, the server MUST ensure that the DNS is updated with a new AAAA record, as specified by the client's FQDN, before responding with the corresponding DHCP Reply. Likewise, if the 'Q' bit is set, and if the 'P' bit is set, the server MUST ensure that the DNS is updated with a new PTR record, as specified by the client's FQDN, before responding with the corresponding DHCP Reply. A DHCP client can include an IP address in its IP Address extension and set the 'A' bit and/or 'P' bit to ask the DHCP Server to use that address for updating DNS. This can be done even with IP addresses obtained by Stateless Address Autoconfiguration [23]. If the client wishes to have its FQDN associated with one of several existing IP addresses which it has received from the DHCP Server, the client MUST supply that IP address in the IP address extension along with the FQDN. 3.1. Client Considerations for the IP Address extension 3.1.1. Address Lifetimes An IP address returned to a client has a preferred and valid lifetime. The valid lifetime represents the lease for addresses provided to the client, from the server. The client SHOULD make a new Request for any address that is about to expire, or request a new address or the same address before the lease actually expires. If the client does not make a new Request Perkins Expires 13 September 1998 [Page 7] Internet Draft DHCPv6 Extensions 13 March 1998 for an address, the server SHOULD assume the client does not want that address. The server MAY provide that address to another client requesting an address. The client MAY request values for the lifetimes, but the client MUST use the lifetimes provided by the server response. When the preferred lifetime of an IP address expires, the client's address becomes a deprecated address. See [9] for required handling of deprecated IP addresses. Before an address for a DHCPv6 client's interface becomes deprecated, the client SHOULD request a new address for that interface, or make a new DHCP Request for the existing address (which can result in the address receiving an updated preferred lifetime). When the client requests an IP address from the DHCPv6 server, the client MUST keep track of when the request was issued. When the client receives a successful reply from the DHCPv6 server, it MUST decrement the received Lifetimes by the amount of time between the transmission of the DHCP Request and the reception of the corresponding DHCP Reply. In this way, the client is best assured that its address lifetimes will not expire at the DHCP Server before they expire at the client. 3.1.2. Use with the DHCP Request message In a DHCP Request (for each address extension), a client MUST set the status code to zero. In a DHCP Request (for each address extension), a client MAY: - include an IP address and/or a DNS name (which may be a host name or a FQDN). - set the 'A' bit to request that the server update DNS with a new AAAA record, as specified by the client's FQDN; if the 'Q' bit is also set, this update MUST be completed before responding with the corresponding DHCP Reply. - set the 'P' bit to request that the server update DNS with a new PTR record, as specified by the client's FQDN; if the 'Q' bit is also set, this update MUST be completed before responding with the corresponding DHCP Reply. - indicate the minimum preferred (and/or valid) lifetime, by supplying a value for the field(s). Perkins Expires 13 September 1998 [Page 8] Internet Draft DHCPv6 Extensions 13 March 1998 - specify whether address, name and lifetimes (if present) are advisory -or- mandatory, by setting the 'Q' bit. If the Request is advisory, a server may send different parameters than requested in the DHCP Reply. Otherwise, if the Request is mandatory, the server MUST reject the Request if it cannot be fulfilled. A server can always supply a greater value for the lifetimes than that requested by the client, even if the 'Q' bit is set. If the client wishes to have a smaller lifetime than the server supplies, the client MAY use the DHCP Release mechanism to relinquish it. A client may include multiple IP Address extensions in a single DHCP Request. The server that receives the Request is not absolutely required to honor the client's Request. A DHCP client indicates that it cannot accept anything other than the configuration information (e.g., IP address) listed in the IP Address extension to the DHCP Request, by specifying the 'Q' (Required) bit. When a client requests an IP address, it MUST maintain a record for the server which allocates that address, so that the client can (if necessary) in the future - Extend the lifetime with the same server, or - Release the address, using DHCP Release. 3.1.3. Receiving as part of the DHCP Reply message When the client receives an IP address extension as part of a DHCP Reply which it accepts (see [4]), it first inspects the status to see whether the requested information has been granted. If the status is nonzero, the client should log the error, display the error condition for action by the user and/or the network administrator. Nonzero status almost always indicates that the client will be need to modify its request before it could be satisfied by the replying DHCP server, or alternatively that the replying DHCP server will need to be given updated configuration information for the client. Upon reception of a new IP address with a lifetime, the client MUST perform Duplicate Address Detection (DAD) [23]; however, if the address has already been allocated to the client and it is merely renewing the lifetime of the address, the client does not have to perform DAD each time. If the client receives an IP address with zero valid lifetime, the client MUST immediately discontinue using that IP address. Perkins Expires 13 September 1998 [Page 9] Internet Draft DHCPv6 Extensions 13 March 1998 3.1.4. Use with the DHCP Release message In DHCP Release (for each address extension): - the client may include an IP address and/or a DNS name (which may be a host name or a FQDN). - the server MUST update DNS to delete the AAAA record or records that the server originally used when updating DNS when the address was allocated to the client, and likewise for the PTR record (regardless of the setting of the 'A' or 'P' bits in the address extension). - If the client, on the other hand, took charge of the DNS updates, it MUST perform the corresponding deletions before issuing the DHCP Release. The client MUST provide a specific IP address in the extension. 3.2. Server Considerations for the IP Address extension 3.2.1. Use with the DHCP Advertise message In DHCP Advertise (for each address extension), the Server can indicate: - the client's FQDN or host name - the preferred lifetime - the valid lifetime - whether DNS will accept new names for the address (via the 'A' bit) If the server sets the 'A' bit, it is willing to perform DNS updates to AAAA records on behalf of the client. Likewise, if the server sets the 'P' bit, it is willing to perform DNS updates to PTR records on behalf of the client. 3.2.2. Receiving a DHCP Request with the IP Address Extension When a server receives a request for an IP address, it consults its allocation tables and determines an IP address appropriate for the requesting client and the link to which the client is attached. The link can be determined by the Agent address prefix in the DHCP Request message header, or, when there is no relay, by the link of Perkins Expires 13 September 1998 [Page 10] Internet Draft DHCPv6 Extensions 13 March 1998 the interface on which the request was received. This is true in the latter case because the client and the server have to be on the same link when there is no server address included in the message header. If the client has requested that the server perform DNS updates as part of the IP address allocation and configuration, the server MUST maintain this fact as part of the client's binding. Then, if the client eventually releases the IP address (see the DHCP Releas message in [4]), the server MUST perform the reverse service by updating DNS again as needed. 3.2.3. Use with the DHCP Reply message In a DHCP Reply message (for each address extension) the server MUST indicate in the IP address extension - the preferred lifetime - the valid lifetime - the status of the request If the Reply is a response to a DHCP Release, the lifetimes MUST both be zero. In a DHCP Reply message, for each address extension) the server MAY indicate - the DNS name - (by setting the 'A' bit) whether AAAA has been updated by the DNS - (by setting the 'P' bit) whether PTR has been updated by the DNS If the client requests updates, and sets the 'Q' bit, the server MUST NOT issue the DHCP Reply until after receiving positive indication that the DNS update has indeed been performed. If the 'Q' bit has been set, and the server cannot honor the IP address extension, it MUST return a DHCP reply with the status 22. Otherwise, the client can subsequently update DNS if needed (i.e., the server didn't do it). If the server receives a DHCP Request from one of its clients whose address it wishes to invalidate, it can cause the client to discontinue use of the old address by including valid and preferred lifetimes with a value of zero. Perkins Expires 13 September 1998 [Page 11] Internet Draft DHCPv6 Extensions 13 March 1998 To perform renumbering, the server will include two IP address extensions, one to reduce the the preferred lifetime and reduce the valid lifetime for the old address, and another to give the client its new address. On a practical note, if the DHCP administrator uses site-local addresses for IP address allocation to clients, there will be less need for renumbering whenever the site moves to a new site prefix or set of site prefixes. Of course, this only works when the site does not need global addresses. 3.2.4. Use with the DHCP Reconfigure message In DHCP Reconfigure (for each address extension) the server MAY indicate the DNS name. 3.2.5. Receiving a DHCP Release with the IP Address Extension When a DHCP client releases its IP address, by including an appropriate IP Address Extension with the DHCP Release message, the server determines whether or not it was originally responsible for updating the DNS AAAA record or PTR record for the client. If so, then the server must also perform the reverse service by updating DNS again to delete the client records. 3.3. DHCP Relay Considerations The DHCP Relay MUST NOT change any information in any DHCPv6 Extension fields. All Extension information flows between DHCPv6 Server and DHCPv6 Client without modification by any Relay. 4. General Extensions The following extensions are important for many DHCPv6 clients, and are not specific to any upper-level protocol. Perkins Expires 13 September 1998 [Page 12] Internet Draft DHCPv6 Extensions 13 March 1998 4.1. Time Offset 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time Offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type for the time offset extension is 2, and its Length is 4 octets. The time offset field specifies the offset of the client's clock in seconds from Coordinated Universal Time (UTC). The offset is expressed as a signed (two's complement) 32-bit integer. 4.2. IEEE 1003.1 POSIX Timezone extension DHCP includes an extension for the specification of the Universal Coordinated Time Offset (type 2, defined in section 4.1), which is defined as a two's complement 32-bit integer representing the offset in seconds from UTC. Unfortunately, the UTC offset extension does not provide enough information for an Internet client to determine such timezone-related details as the timezone names, daylight savings time start and end times in addition to the timezone UTC offsets. This extension (analogous to that proposed for DHCPv4 [6]) allows delivery of timezone information in the form of a IEEE 1003.1 POSIX Timezone specifier [13]. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IEEE 1003.1 POSIX Timezone string (variable length) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The extension type is 3. This IEEE 1003.1 POSIX Timezone is detailed next, in section 4.2.1. 4.2.1. IEEE 1003.1 POSIX Timezone specifier . The format of the IEEE 1003.1 POSIX timezone string is specified as StdOffset[Dst[Offset],[Start[/Time],End[/Time]]] Perkins Expires 13 September 1998 [Page 13] Internet Draft DHCPv6 Extensions 13 March 1998 where '[' and ']' enclose optional fields, '|' indicates choice of exactly one of the alternatives, ',' and '/' represent literal characters present in the string, and: Std three or more octets for the standard timezone (Std). Any characters (or case) except a leading colon, digits, comma, minus or plus sign are allowed. Offset Indicates the value one must add to local time to arrive at UTC, of the form: [+|-]hh[:mm[:ss]]. Offset following Std is required. Digits are always interpreted as decimal number. If preceded by a '-', the timezone is east of the Prime Meridian, otherwise it is west ('+' is optional) The permissible values for hh[:mm[:ss]] are as follows: hh 0 <= hh <= 23 mm 0 <= mm <= 60 ss 0 <= ss <= 60 Offset has no default value. Dst three or more octets for the daylight savings timezone. If Dst is missing, then daylight savings time does not apply in this locale. If no Offset follows Dst, then Dst is assumed to be one hour ahead of standard time. Any characters (or case) except a leading colon, digits, comma, minus or plus sign are allowed. Start Indicates the day of the year, in one of the formats indicated below, when to change to daylight savings time. The 'Time' field (which follows immediately after a '/' character, if present) indicates when the change is made, in local time. End Indicate the day of the year, in one of the formats indicated below, when to change back from daylight savings time. The 'Time' field (which follows immediately after a '/' character, if present) indicates when the change is made, in local time. Time Time has the same format as Offset, except that no leading '-' or '+' is permitted. The default is 02:00:00. The day of the year can be given in one of the following formats: Perkins Expires 13 September 1998 [Page 14] Internet Draft DHCPv6 Extensions 13 March 1998 Jn The julian day n, (1 <= n <= 365). Leap days are not counted. n zero-based julian day, (0 <= n <= 365). Leap days are counted so it is possible to refer to Feb 29. Mm.n.d The 'd'th day, (0 <= d <= 6) of week 'n' of month 'm' of the year (1 <= n <= 5, 1 <= m <= 12, where week 5 means last 'd' day in month 'm' which may occur in either the fourth or the fifth week. Week '1' is the first week in which the 'd' day occurs. 4.2.2. An Example For Eastern USA time zone, 1986, the Posix timezone string is as follows: EST5EDT4,116/02:00:00,298/02:00:00 4.2.3. Timezone Extension Precedence If a DHCP client receives both the Time Offset (type 2) and the POSIX Timezone (type 3) extension in a DHCP reply message, the client MUST discard the value of the Time Offset (type 2) extension and utilize the POSIX Timezone Extension. The DHCP client MAY notify the user that it is resolving the conflict by discarding the Time Offset (type 2) extension. If a DHCP client finds that the POSIX Timezone extension value is misformatted, it SHOULD notify the the user of the problem and MUST discard the entire extension value. 4.3. Domain Name Server Extension 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Domain Name System server addresses | | (16 octets each) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The domain name server extension specifies a list of Domain Name System [19] name servers available to the client. Servers SHOULD be listed in order of preference. Perkins Expires 13 September 1998 [Page 15] Internet Draft DHCPv6 Extensions 13 March 1998 The Type for the domain name server extension is 6. The minimum Length for this extension is 16 octets, and the Length MUST always be a multiple of 16. 4.4. Domain Name This extension specifies the default domain name that client should use when resolving hostnames via the Domain Name System. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Domain Name (variable length) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type for this extension is 10. Its minimum Length is 1. The domain name is a ASCII string, Length octets in size. If the Domain Name extension is not specified, and the IP Address extension received by a client contains a FQDN, then the client may take the part of the FQDN after the first '.' octet as the Domain Name. 5. Application and Service Parameters This section details some miscellaneous extensions used to configure miscellaneous applications and services. 5.1. Directory Agent Extension Entities using the Service Location Protocol [24] need to find out the address of Directory Agents in order to transact messages. They may need to discover the correct scope to be used in conjunction with the service attributes which are exchanged using the Service Location Protocol. The scope MAY be denoted in any standardized character set. This extension requests or specifies a Directory Agent (DA), along with zero or more scopes supported by that DA. Note that this extension MAY be included multiple times in the same DHCP Request or DHCP Reply. If so, then the extensions SHOULD be included in order of decreasing preference. Perkins Expires 13 September 1998 [Page 16] Internet Draft DHCPv6 Extensions 13 March 1998 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |D|F|M|S| reserved | DA length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Directory Agent (variable length) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (if present) Typed-Scope-List (variable length) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 16 Length (unsigned integer, variable) The length of the Extension in octets. D If the 'D' bit is set, the Directory Agent field and the DA Length fields are present. F If the 'F' bit is set, the Directory Agent is indicated by including its variable length host name or Fully Qualified Domain Name (FQDN) instead of its IP address. M If the 'M' bit is set, the Directory Agent address is the only one that may be used, and multicast methods for discovering Directory Agents MUST NOT be used. S If the 'S' bit is set, the scope is present. rsv reserved; ignored upon reception; MUST be sent as zero DA Length The length (in octets) of the Directory Agent field. Directory Agent The Fully Qualified Domain Name (FQDN), host name, or IP address of the Directory Agent. Typed Scope List The characters denoting the scope (see Section reftsl). In order to simplify administration of the configuration of Directory Agents for Service Location Protocol clients, the Directory Agent can be indicated by presenting its FQDN or host name instead of its IP address. This allows renumbering to proceed more smoothly [7]. When the FQDN or host name is used, the server sets the 'F' bit. The host name can be distinguished from the FQDN by the presence of a '.' character. In any case, the DA length field is set to be the length Perkins Expires 13 September 1998 [Page 17] Internet Draft DHCPv6 Extensions 13 March 1998 of the Directory Agent field. When the 'F' bit is not set, the DA Length MUST be 16. Note that more than one Directory Agent extension may be present in a DHCP message. Each such extension may have the same or different scope. The client may request any Directory Agent with a particular scope, by including the Directory Agent extension in a DHCP Request message with no Directory Agent address included (the 'D' bit set to zero), and the characters denoting the scope. The length of the Typed Scope List is only indicated implicitly by the overall length of the extension. This string is NOT null terminated. The format of the Typed Scope List field is described in section 2.2. Extension 16 MUST include one or more scopes if a DA address is returned. Using extension 16, it is not possible for different service types on the same node to be configured with different directory agents. In other words, all service types on the same node will be configured with the same directory agent. 5.2. Service Scope Extension This extension indicates a scope that should be used by a Service Agent (SA) [24], when responding to Service Request messages as specified by the Service Location Protocol. This extension MAY be included multiple times in the same DHCP Request or DHCP Reply. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Typed-Scope-List ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 17 Length (unsigned integer, variable) The length of the Extension in octets. Typed-Scope-List see Section 2.2. Perkins Expires 13 September 1998 [Page 18] Internet Draft DHCPv6 Extensions 13 March 1998 The Typed-Scope-List is described in Section 2.2. The DHCP client (i.e., user agent or service agent) which receives this extension will use the indicated scope for in all SLP requests and registrations. The scope string must be UTF8 character encoded. This string is not null terminated. DHCP clients MAY use extension 79 to request scopes for one or more particular service types. Note that more than one Service Scope extension may be present in a DHCP message. The length of the scope is only indicated implicitly by the overall length of the extension. 5.3. Network Time Protocol Servers Extension This extension specifies a list of IP addresses indicating NTP [17] servers available to the client. Servers SHOULD be listed in order of preference. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NTP server addresses | | (16 octets each) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The type for this extension is 18. Its minimum Length is 16, and the Length MUST be a multiple of 16. 5.4. Network Information Service Domain Extension This extension specifies the name of the client's NIS [16] domain. The domain is formatted as a character string consisting of characters from the US-ASCII character set. The type for this extension is 19. Its minimum Length is 1. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NIS Domain Name (variable length) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Perkins Expires 13 September 1998 [Page 19] Internet Draft DHCPv6 Extensions 13 March 1998 5.5. Network Information Servers Extension This extension specifies a list of IP addresses indicating NIS [16] servers available to the client. Servers SHOULD be listed in order of preference. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NIS server addresses | | (16 octets each) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The type for this extension is 20. Its minimum Length is 16, and the Length MUST be a multiple of 16. 5.6. Network Information Service+ Domain Extension This extension specifies the name of the client's NIS+ [16] domain. The domain is formatted as a character string consisting of characters from the US-ASCII character set. The type for this extension is 21. Its minimum Length is 1. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NIS+ Client Domain Name (variable length) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 5.7. Network Information Service+ Servers Extension This extension specifies a list of IP addresses indicating NIS+ [16] servers available to the client. Servers SHOULD be listed in order of preference. Perkins Expires 13 September 1998 [Page 20] Internet Draft DHCPv6 Extensions 13 March 1998 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NIS+ server addresses | | (16 octets each) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The code for this extension is 22. Its minimum Length is 16, and the Length MUST be a multiple of 16. 6. TCP Parameters This section lists the extensions that affect the operation of the TCP layer on a per-interface basis. 6.1. TCP Keepalive Interval Extension 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Keepalive Time Interval | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This extension specifies the interval (in seconds) that the client TCP should wait before sending a keepalive message on a TCP connection. The time is specified as a 32-bit unsigned integer. A value of zero indicates that the client should not generate keepalive messages on connections unless specifically requested by an application. The Type for this extension is 32, and its Length is 4. 7. DHCPv6 Extensions This section details the extensions that are specific to DHCPv6. 7.1. Maximum DHCPv6 Message Size Extension This extension specifies the maximum size in octets of any DHCPv6 message that the sender of the extension is willing to accept. The Perkins Expires 13 September 1998 [Page 21] Internet Draft DHCPv6 Extensions 13 March 1998 size is specified as an unsigned 16-bit integer. A client may use the maximum DHCPv6 message size extension in DHCP Request messages, but MUST NOT use the extension in other DHCP messages (see [4]). 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Max DHCPv6 Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type for this extension is 40, and its Length is 2. The minimum permissible value is 1500. 7.2. Platform Specific Information A platform is defined as the combination of hardware and operating system (OS). This extension is used by clients and servers to exchange client-platform-specific information. The information is an opaque collection of data, presumably interpreted by platform-specific code on the clients. The definition of this information is platform specific. Clients identify their platform through the use of the Platform Class identifier extension (see Section 7.3). Clients which do not receive platform specific information SHOULD make an attempt to operate without it, although they may do so (and announce that they are doing so) in a degraded mode. If a Platform vendor encodes more than one item of information in this extension, then the vendor MUST encode the extension using "Encapsulated platform-specific extensions" as described below. The Encapsulated platform-specific extensions field MUST be encoded as a sequence of type/length/value fields of identical syntax to the form defined for DHCPv6 extensions. Extension 65535 (END), if present, signifies the end of the encapsulated platform extensions, not the end of the platform extensions field. If no extension 65535 is present, then the end of the enclosing platform-specific information field is taken as the end of the encapsulated platform-specific extensions field. Perkins Expires 13 September 1998 [Page 22] Internet Draft DHCPv6 Extensions 13 March 1998 The Type for this extension is 48 and its minimum Length is 4. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Platform-specific extension information ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ When encapsulated platform-specific extensions are used, each one has the same format as just shown. In other words, all platform-specific extensions are encoded in Type-Length-Value (TLV) format. More than one platform-specific extension can, therefore, be included in the same DHCP "Platform Specific Information" extension. DHCP servers which support the configuration of Platform Specific Information extensions, and which have been configured with configuration information specific to some number of Platform Class Identifiers MUST select and return only those platform-specific extensions which match the Platform Class Identifier provided by the DHCP client. 7.3. Platform Class Identifier This extension is used by a DHCP client to identify the hardware type and operating system platform it is hosted on. The extension value itself is an opaque value to a DHCP server, and is only used by the DHCP server to "lookup" Platform Specific Extensions associated with clients of a certain platform class. Servers not equipped to interpret the platform class identifier specified by a client MUST ignore it (although it may be reported). Otherwise, servers SHOULD respond with the set of extensions corresponding to the platform class identifier specified by the client. Note that unlike the User Class Identifier, the Platform Class Identifier does not need to be echoed back to the DHCP client because there can be one and only one Platform Class Identifier for a 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Char Encoding | Platform Class Identifier ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Perkins Expires 13 September 1998 [Page 23] Internet Draft DHCPv6 Extensions 13 March 1998 The Type for this extension is 49. The platform class identifier is a string of characters in the character set specified by the Char Encoding field (see section 2.1), of length "Length"-2 octets. The platform class identifier represents the hardware and Operating system class of which the client is a member. In order to prevent collisions in the Platform Class Identifier namespace, we recommend that platform vendors prefix their Platform Class Identifiers with their Stock symbol or some other globally recognized authority. For example, Platform Class Identifiers for Sun Microsystems Inc platforms would be prefaced by "SUNW", the NASDAQ stock symbol for Sun. 7.4. Class Identifier This extension is used by a DHCP client to optionally identify the type or category of user or applications it represents. DHCP administrators may define specific class identifiers to convey information about a client's software configuration or about its user's preferences. For example, an identifier may specify that a particular DHCP client is a member of the class "accounting auditors", which have special service needs such as a particular database server. Alternatively, the identifier may encode the client's hardware configuration. Servers not equipped to interpret the class identifier specified by a client MUST ignore it (although it may be reported). Otherwise, servers SHOULD respond with the set of extensions corresponding to the class identifier specified by the client. Further, if the server responds with the set of extensions corresponding to the given class identifier, it MUST return this extension (with the given class identifier value) to 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Char Encoding | Class Identifier ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type for this extension is 64. The class identifier is a string of characters in the character set specified by the Char Encoding field (see section 2.1), of length "Length"-2 octets. The class identifier represents the class identifier of which the client is a member. Perkins Expires 13 September 1998 [Page 24] Internet Draft DHCPv6 Extensions 13 March 1998 7.5. Reconfigure Multicast Address A DHCPv6 server can instruct its clients to join a multicast group for the purposes of receiving DHCPv6 Reconfigure messages. This will allow a server to reconfigure all of its clients at once; such a feature will be useful when renumbering becomes necessary. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reconfigure Multicast Address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type of the Reconfigure Multicast Address is 66, and the Length is 16. 7.6. Renumber DHCPv6 Server Address A DHCPv6 server can instruct its clients to change their internal records to reflect the server's newly renumbered IP address, by using the "Renumber DHCPv6 Server Address" extension. This extension may be sent with the DHCP Reconfigure message, and thus can be multicast to all of the server's clients instead of being unicast to each one individually. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | New DHCPv6 Server Address | | (16 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type of the Renumber DHCPv6 Server Address is 67, and the Length is 16. 7.7. DHCP Relay ICMP Error Message Format A DHCP Relay ICMP Message extension is used to inform a client of an ICMP Error message the relay received after forwarding a client Solicit or Request message. Perkins Expires 13 September 1998 [Page 25] Internet Draft DHCPv6 Extensions 13 March 1998 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ICMP Error Message | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type of the DHCP Relay ICMP Message extension is 68, and the Length is the length of the ICMP error message received by the relay [8]. 7.7.1. ICMP Extension Client Considerations When a client sends a Solicit or Request message it can be forwarded by a relay. When the relay forwards messages for a client the network may return an ICMP error [8] message to the relay. If the relay can determine the client's link-local address within the UDP payload of the ICMP returned error message payload, the relay will send the client a DHCP Relay ICMP Error message as defined in section 7.7.2. The client MAY record these messages based on the ICMP type and reason codes provided in the ICMP Error payload [8], for future use or for system logging purposes. How the client uses this information is implementation dependent. 7.7.2. ICMP Extension Relay Considerations If the relay receives an ICMP error message after forwarding a client Solicit or Request message, it should look in the payload of the ICMP message [8], to see if it can determine the clients link-local address in the server Advertise or Reply message. If it can the relay should forward a DHCP Relay ICMP Error message received to the client as specified in section 7.7.1, by using the clients link-local address from the ICMP error message as the IP source address in the IP header sent to the client. If the relay cannot determine the clients link-local address in the ICMP error message the packet MUST be silently discarded. 7.8. Client-Server Authentication Extension Exactly one Client-Server Authentication Extension MAY be present in any DHCPv6 message transmitted between a client and server (or vice-versa). If present, it MUST be the last extension. Perkins Expires 13 September 1998 [Page 26] Internet Draft DHCPv6 Extensions 13 March 1998 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Security Parameters Index (SPI) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Replay Protection | | (8 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Authenticator (variable length) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 84 Length (unsigned integer, variable) 4 for the SPI, plus 8 for the replay protection, plus the number of octets in the Authenticator. SPI A Security Parameters index [2] identifying which security context among those available between the DHCPv6 client and server. Replay Protection A 64-bit timestamp (in Network Time Protocol [18](NTP) format) (see section 9.1). Authenticator (variable length) (See Section 9.2.) This authentication extension remedies the inability of IPsec to provide for non end-to-end authentication, since authentication is needed even when the client has no IPv6 address of large enough scope to reach the DHCP server. The extension can be originated by either the DHCPv6 Client or DHCPv6 server to authenticate the rest of the data in the DHCPv6 message. The default authentication algorithm is defined in section 9.2. Note that SPI values 0 through 255 are reserved and, if used, MUST conform to the security context defined by that value in the most recent Assigned Numbers RFC (e.g., [21]). 7.9. Client Key Selection Extension A DHCPv6 server may wish to indicate to a prospective client which SPI it must use to authenticate subsequent messages, using the Client-Server Authentication Extension. In such cases, the server Perkins Expires 13 September 1998 [Page 27] Internet Draft DHCPv6 Extensions 13 March 1998 includes the Client Key Selection Extension in its DHCP Advertise message. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Security Parameters Index (SPI) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 85 Length 4 SPI A Security Parameters index [2] identifying a security context between a pair of nodes among the contexts available in the security association defined between the DHCPv6 client and server. SPI values 0 through 255 are reserved and, if used, MUST conform to the security context defined by that value as defined in the most recent Assigned Numbers RFC (e.g., [12]). 8. End extension specification The end extension marks the end of valid information in the vendor field. The Type for the end extension is 65535, and its Length is 2 octets; there is no Length field for the end extension. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 65535 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 9. Security Considerations There is an urgent need to define some security protocol for use with DHCPv6, since otherwise malicious parties could create numerous denial-of-service style attacks based on depleting available server resources or providing corrupted or infected data to unsuspecting clients. The following sections discuss aspects of security relevant for users of the Client-Server Authentication extension 7.8. See also the Security Considerations in the companion specification [4]. Perkins Expires 13 September 1998 [Page 28] Internet Draft DHCPv6 Extensions 13 March 1998 9.1. Replay Protection A 64-bit timestamp, in Network Time Protocol [18](NTP) format, is used to protect against replay of previous authenticated messages by malicious agents. The NTP timestamp value used in the extension MUST be chosen, and verified, to be larger than values used by the originator in previous Client-Server Authentication extensions. On the other hand, the timestamp value MUST also be chosen (and verified) to be no greater than one year more than the last known value (if any) used by the originator. 9.2. Default Authentication Algorithm The default authentication algorithm is HMAC [15], using keyed-MD5 [22]. Given a secret key K, and "data" the information to be authenticated, HMAC_result is computed as follows: 1. opad := 0x36363636363636363636363636363636 (128 bits) 2. ipad := 0x5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C (128 bits) 3. zero_extended_key := K extended by zeroes to be 128 bits long 4. opadded_key := zero_extended_key XOR opad 5. ipadded_key := zero_extended_key XOR ipad 6. HMAC_result := MD5 (opadded_key , MD5 (ipadded_key, data)) The key K is the shared secret defined by the security association between the client and server and by the SPI value specified in the Authentication Extension. The "data" is the stream of octets in all previous fields in the DHCPv6 message and extensions. The authenticator is the 128-bit value HMAC_result. 10. Defining New Extensions Implementation specific use of undefined extensions (including those in the range 86-32767) may conflict with other implementations, and registration is required. The author of a new DHCP extension MUST follow these steps to obtain acceptance of the extension as a part of the DHCP Internet Standard: 1. The author devises the new extension. Perkins Expires 13 September 1998 [Page 29] Internet Draft DHCPv6 Extensions 13 March 1998 2. The author requests a number for the new extension from IANA by contacting: Internet Assigned Numbers Authority (IANA) USC/Information Sciences Institute 4676 Admiralty Way Marina del Rey, California 90292-6695 or by email as: iana@isi.edu 3. The author documents the new extension, using the newly obtained extension number, as an Internet Draft. 4. The author submits the Internet Draft for review through the IETF standards process as defined in "Internet Official Protocol Standards" [14]. The new extension will be submitted for eventual acceptance as an Internet Standard. 5. The new extension progresses through the IETF standards process; the new extension will be reviewed by the Dynamic Host Configuration Working Group (if that group still exists), or as an Internet Draft not submitted by an IETF working group. 6. If the new extension fails to gain acceptance as an Internet Standard, the assigned extension number will be returned to IANA for reassignment. This procedure for defining new extensions will ensure that: * allocation of new extension numbers is coordinated from a single authority, * new extensions are reviewed for technical correctness and appropriateness, and * documentation for new extensions is complete and published. Perkins Expires 13 September 1998 [Page 30] Internet Draft DHCPv6 Extensions 13 March 1998 11. Acknowledgements Thanks to Jim Bound for his frequent review, helpful suggestions, and design assistance. Ralph Droms has also made many, many suggestions which have been incorporated into this draft. The original form of this internet draft was copied directly from RFC1533 [1], written by Steve Alexander and Ralph Droms. Thanks to Mike Carney for his many helpful comments, as well as contributing the design of the Platform Specific Information and Platform Class Identifier. Thanks to Erik Guttman for his helpful suggestions for the Service Location extensions. Thanks to Matt Crawford and Erik Nordmark for their careful review as part of the Last Call process. Jim Bound also provided all the necessary design and text for the DHCP Relay ICMP Error Message Extension. References [1] S. Alexander and R. Droms. DHCP Options and BOOTP Vendor Extensions. RFC 1533, October 1993. [2] R. Atkinson. IP Authentication Header. RFC 1826, August 1995. [3] T. Berners-Lee, L. Masinter, and M. McCahill. Uniform Resource Locators (URL). RFC 1738, December 1994. [4] J. Bound and C. Perkins. Dynamic Host Configuration Protocol for IPv6. draft-ietf-dhc-dhcpv6-11.txt, May 1997. (work in progress). [5] S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. RFC 2119, March 1997. [6] M. W. Carney. DHCP Option for IEEE 1003.1 POSIX Timezone Specifications. draft-ietf-dhc-timezone-01.txt, January 1997. (work in progress). [7] B. Carpenter and Y. Rekhter. Renumbering needs work. RFC 1900, February 1996. [8] A. Conta and S. Deering. Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6). RFC 1885, December 1995. [9] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6) Specification. RFC 1883, December 1995. Perkins Expires 13 September 1998 [Page 31] Internet Draft DHCPv6 Extensions 13 March 1998 [10] E. Guttman, C. Perkins, and J. Kempf. Service Templates and service: Schemes. draft-ietf-svrloc-service-scheme-05.txt, November 1997. (work in progress). [11] E. Guttman, C. Perkins, J. Veizades, and M. Day. Service Location Protocol version 2. draft-ietf-svrloc-protocol-v2-04.txT, March 1998. (work in progress). [12] Stan Hanks, Tony Li, Dino Farinacci, and Paul Traina. Generic Routing Encapsulation (GRE). RFC 1701, October 1994. [13] IEEE. 1003.1 POSIX Timezone Specification, 1988. [14] Editor J. Postel. INTERNET OFFICIAL PROTOCOL STANDARDS. STD 1, July 1997. [15] H. Krawczyk, M. Bellare, and R. Cannetti. HMAC: Keyed-Hashing for Message Authentication. RFC 2104, February 1997. [16] Sun Microsystems. System and Network Administration, March 1992. [17] D. Mills. Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI. RFC 2030, October 1996. [18] David L. Mills. Network Time Protocol (Version 3): Specification, Implementation and Analysis. RFC 1305, March 1992. [19] P. Mockapetris. Domain Names - Concepts and Facilities. IETF STD 13, November 1987. [20] Joyce K. Reynolds and Jon Postel. Assigned Numbers. STD 2, October 1994. [21] Joyce K. Reynolds and Jon Postel. Assigned Numbers. RFC 1700, October 1994. [22] Ronald L. Rivest. The MD5 Message-Digest Algorithm. RFC 1321, April 1992. [23] S. Thomson and T. Narten. IPv6 Stateless Address Autoconfiguration. RFC 1971, August 1996. [24] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service Location Protocol. RFC 2165, July 1997. [25] P. Vixie, S. Thomson, Y. Rekhter, and J. Bound. Dynamic Updates in the Domain Name System (DNS). RFC 2136, April 1997. Perkins Expires 13 September 1998 [Page 32] Internet Draft DHCPv6 Extensions 13 March 1998 Chair's Addresses 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 EMail: droms@bucknell.edu Author's Address Questions about this memo can be directed to: Charles E. Perkins Technology Development Group Mail Stop MPK15-214 Room 2682 Sun Microsystems, Inc. 901 San Antonio Road Palo Alto, California 94303 USA Phone: +1-650-786-6464 Fax: +1-650-786-6445 email: charles.perkins@Sun.COM Perkins Expires 13 September 1998 [Page 33]