Network Working Group A.K. Vijayabhaskar Internet-Draft Hewlett-Packard Expires: Dec 19, 2002 19 Jun 2002 Client Preferred Prefix option for DHCPv6 draft-ietf-dhc-dhcpv6-opt-cliprefprefix-00.txt Status of this Memo 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. This Internet-Draft will expire on July 10, 2002. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes the Client Preferred Prefix option by which the client can specify its preferred prefixes on which the addresses need to be allocated by the server. 1. Introduction Scenario 1: The client's link has multiple prefixes of different scopes and the administrator policy on the server insists that the addresses need to be allocated on site-local prefixes only. The client will not be able to communicate with a node that belongs to a different site, as the server allocates only site-local addresses in IAs. Scenario 2: The client's link has two prefixes: site-local and global. The administrator policy insists that addresses need to be allocated on both the prefixes. All the nodes on a link will not communicate with external sites and thus all of them do not require global Vijayabhaskar A K Expires December 19, 2002 [Page 1] Internet-Draft Client Preferred Prefix option for DHCPv6 Jun 2002 addresses. However, the server allocates addresses on both the prefixes and hence most of the global addresses are wasted. To overcome the problems described in Scenario 1 and 2, the client can specify its preferred prefixes to the server using Client Preferred Prefix option. 2. Requirements The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in RFC 2119 [1] 3. Terminology This document uses terminology specific to IPv6 and DHCPv6 as defined in section "Terminology" of the DHCP specification. 4. Client Preferred Prefix option Client Preferred Prefix option is used by the client to specify its preferred prefixes to the server. The format of the Client Preferred Prefix option is as shown below: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_CLIENT_PREF_PREFIX | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | prefix-len | | +-+-+-+-+-+-+-+-+-+ | | | | subnet prefix (n bytes) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | prefix-len | | +-+-+-+-+-+-+-+-+-+ | | | | subnet prefix (n bytes) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . client-pref-prefix-options . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code: OPTION_CLIENT_PREF_PREFIX (tbd) option-len: total length of the prefix-len and subnet prefix lists and its encapsulated options. prefix-len: prefix length of the subnet address. Vijayabhaskar A K Expires December 19, 2002 [Page 2] Internet-Draft Client Preferred Prefix option for DHCPv6 Jun 2002 subnet prefix: 'n' bytes of subnet prefix, where 'n' is minimum number of bytes required to refer 'prefix-len' bits of the prefix. client-pref-prefix-options: options associated with Client Preferred Prefix option. 5. Server Behavior If the server policy doesn't support client preferred prefix option, then it can either send reply with OptionUnsupported in the encapsulated error code option in client preferred prefix option or allocate addresses based on its original policy. The server behavior SHOULD be configurable by the administrator. If the server policy supports client preferred prefix option and if this option contains one or more prefixes which are not valid for the client's link, then, the server MUST send the reply with error code NotOnLink. If the server policy supports client preferred prefix option and all the prefixes in this option are valid for the client's link, then the server MUST allocate addresses only on the prefixes specified in client preferred prefix option encapsulated in the IAs. 6. Client Behavior If the client has received OptionUnsupported error, it can either choose the next server to send request, till the server list gets exhausted or it can start the configuration exchange as specified in Section 18.1.1 of [2] without the client preferred prefix option. If the server list has exhausted then, it MUST start the configuration exchange as specified in Section 18.1.1 of [2] without the client preferred prefix option. If the client has received the addresses with the prefixes that were not specified in client preferred prefix option, it can release the unwanted addresses. 7. Appearance of these options Client Preferred Prefix option MUST occur only in Request and Reply messages. This option MUST occur in Reply messages only if it encapsulates the Error code option. Client Preferred Prefix option MUST occur only as an encapsulated option in the IA or IA_TA option. Client Preferred Prefix option MUST only have Error code option as the encapsulated option. Vijayabhaskar A K Expires December 19, 2002 [Page 3] Internet-Draft Client Preferred Prefix option for DHCPv6 Jun 2002 8. Security Considerations Since, this option can occur only in IA or IA_TA option, all the IA-relevant security considerations are applicable to this option too. To avoid attacks through this option, the DHCP client SHOULD use authenticated DHCP (see section "Authentication of DHCP messages" in the DHCPv6 specification [2]). 9. IANA Considerations IANA is requested to assign an option code to this option from the option-code space defined in section "DHCPv6 Options" of the DHCPv6 specification [2]. References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R. Droms (ed.), "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-26 (work in progress), June 2002. Author's Addresses Vijayabhaskar A K Hewlett-Packard ESD-I 29, Cunningham Road Bangalore - 560052 India Phone: +91-80-2051424 E-Mail: vijayak@india.hp.com Vijayabhaskar A K Expires December 19, 2002 [Page 4] Internet-Draft Client Preferred Prefix option for DHCPv6 Jun 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. 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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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Thanks to Jim Bound for his thorough review of the document. Vijayabhaskar A K Expires December 19, 2002 [Page 5]