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Vijayabhaskar 2 Internet-Draft Hewlett-Packard 3 Expires: Dec 19, 2002 19 Jun 2002 5 Client Preferred Prefix option for DHCPv6 6 draft-ietf-dhc-dhcpv6-opt-cliprefprefix-00.txt 8 Status of this Memo 10 This document is an Internet-Draft and is in full conformance with 11 all provisions of Section 10 of RFC2026. 13 Internet-Drafts are working documents of the Internet Engineering 14 Task Force (IETF), its areas, and its working groups. Note that 15 other groups may also distribute working documents as Internet- 16 Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six months 19 and may be updated, replaced, or obsoleted by other documents at any 20 time. It is inappropriate to use Internet-Drafts as reference 21 material or to cite them other than as "work in progress." 23 The list of current Internet-Drafts can be accessed at 24 http://www.ietf.org/ietf/1id-abstracts.txt. 26 The list of Internet-Draft Shadow Directories can be accessed at 27 http://www.ietf.org/shadow.html. 29 This Internet-Draft will expire on July 10, 2002. 31 Copyright Notice 33 Copyright (C) The Internet Society (2002). All Rights Reserved. 35 Abstract 37 This document describes the Client Preferred Prefix option by which 38 the client can specify its preferred prefixes on which the addresses 39 need to be allocated by the server. 41 1. Introduction 43 Scenario 1: The client's link has multiple prefixes of different 44 scopes and the administrator policy on the server insists that the 45 addresses need to be allocated on site-local prefixes only. The 46 client will not be able to communicate with a node that belongs to a 47 different site, as the server allocates only site-local addresses in 48 IAs. 50 Scenario 2: The client's link has two prefixes: site-local and global. 51 The administrator policy insists that addresses need to be allocated 52 on both the prefixes. All the nodes on a link will not communicate 53 with external sites and thus all of them do not require global 54 addresses. However, the server allocates addresses on both the 55 prefixes and hence most of the global addresses are wasted. 57 To overcome the problems described in Scenario 1 and 2, the client 58 can specify its preferred prefixes to the server using Client 59 Preferred Prefix option. 61 2. Requirements 63 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, 64 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this 65 document, are to be interpreted as described in RFC 2119 [1] 67 3. Terminology 69 This document uses terminology specific to IPv6 and DHCPv6 as defined 70 in section "Terminology" of the DHCP specification. 72 4. Client Preferred Prefix option 74 Client Preferred Prefix option is used by the client to specify its 75 preferred prefixes to the server. 77 The format of the Client Preferred Prefix option is as shown below: 79 0 1 2 3 80 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 81 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 82 | OPTION_CLIENT_PREF_PREFIX | option-len | 83 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 84 | prefix-len | | 85 +-+-+-+-+-+-+-+-+-+ | 86 | | 87 | subnet prefix (n bytes) | 88 | | 89 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 90 | prefix-len | | 91 +-+-+-+-+-+-+-+-+-+ | 92 | | 93 | subnet prefix (n bytes) | 94 | | 95 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 96 | ... | 97 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 98 . . 99 . client-pref-prefix-options . 100 . . 101 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 103 option-code: OPTION_CLIENT_PREF_PREFIX (tbd) 105 option-len: total length of the prefix-len and subnet prefix lists 106 and its encapsulated options. 108 prefix-len: prefix length of the subnet address. 110 subnet prefix: 'n' bytes of subnet prefix, where 'n' is minimum 111 number of bytes required to refer 'prefix-len' bits 112 of the prefix. 114 client-pref-prefix-options: options associated with Client 115 Preferred Prefix option. 117 5. Server Behavior 119 If the server policy doesn't support client preferred prefix option, 120 then it can either send reply with OptionUnsupported in the 121 encapsulated error code option in client preferred prefix option or 122 allocate addresses based on its original policy. The server behavior 123 SHOULD be configurable by the administrator. 125 If the server policy supports client preferred prefix option and if 126 this option contains one or more prefixes which are not valid for the 127 client's link, then, the server MUST send the reply with error code 128 NotOnLink. 130 If the server policy supports client preferred prefix option and all 131 the prefixes in this option are valid for the client's link, then the 132 server MUST allocate addresses only on the prefixes specified in 133 client preferred prefix option encapsulated in the IAs. 135 6. Client Behavior 137 If the client has received OptionUnsupported error, it can either 138 choose the next server to send request, till the server list gets 139 exhausted or it can start the configuration exchange as specified in 140 Section 18.1.1 of [2] without the client preferred prefix option. 142 If the server list has exhausted then, it MUST start the configuration 143 exchange as specified in Section 18.1.1 of [2] without the client 144 preferred prefix option. 146 If the client has received the addresses with the prefixes that were 147 not specified in client preferred prefix option, it can release the 148 unwanted addresses. 150 7. Appearance of these options 152 Client Preferred Prefix option MUST occur only in Request and Reply 153 messages. This option MUST occur in Reply messages only if it 154 encapsulates the Error code option. 156 Client Preferred Prefix option MUST occur only as an encapsulated 157 option in the IA or IA_TA option. 159 Client Preferred Prefix option MUST only have Error code option as the 160 encapsulated option. 162 8. Security Considerations 164 Since, this option can occur only in IA or IA_TA option, all the 165 IA-relevant security considerations are applicable to this option too. 167 To avoid attacks through this option, the DHCP client SHOULD use 168 authenticated DHCP (see section "Authentication of DHCP messages" 169 in the DHCPv6 specification [2]). 171 9. IANA Considerations 173 IANA is requested to assign an option code to this option from the 174 option-code space defined in section "DHCPv6 Options" of the DHCPv6 175 specification [2]. 177 References 179 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 180 Levels", BCP 14, RFC 2119, March 1997. 182 [2] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R. 183 Droms (ed.), "Dynamic Host Configuration Protocol for IPv6 184 (DHCPv6)", draft-ietf-dhc-dhcpv6-26 (work in progress), June 185 2002. 187 Author's Addresses 189 Vijayabhaskar A K 190 Hewlett-Packard ESD-I 191 29, Cunningham Road 192 Bangalore - 560052 193 India 195 Phone: +91-80-2051424 196 E-Mail: vijayak@india.hp.com 198 Full Copyright Statement 200 Copyright (C) The Internet Society (2002). All Rights Reserved. 202 This document and translations of it may be copied and furnished to 203 others, and derivative works that comment on or otherwise explain it 204 or assist in its implementation may be prepared, copied, published 205 and distributed, in whole or in part, without restriction of any 206 kind, provided that the above copyright notice and this paragraph are 207 included on all such copies and derivative works. However, this 208 document itself may not be modified in any way, such as by removing 209 the copyright notice or references to the Internet Society or other 210 Internet organizations, except as needed for the purpose of 211 developing Internet standards in which case the procedures for 212 copyrights defined in the Internet Standards process must be 213 followed, or as required to translate it into languages other than 214 English. 216 The limited permissions granted above are perpetual and will not be 217 revoked by the Internet Society or its successors or assigns. 219 This document and the information contained herein is provided on an 220 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 221 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 222 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 223 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 224 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 226 Acknowledgement 228 Funding for the RFC Editor function is currently provided by the 229 Internet Society. Thanks to Jim Bound for his thorough review 230 of the document.