--- 1/draft-ietf-dhc-subnet-option-01.txt 2006-02-04 23:05:59.000000000 +0100 +++ 2/draft-ietf-dhc-subnet-option-02.txt 2006-02-04 23:05:59.000000000 +0100 @@ -1,121 +1,127 @@ - Network Working Group G. Waters INTERNET-DRAFT Nortel Networks - March 1999 + June 1999 The Subnet Selection Option for DHCP - - Tuesday, March 23, 1999, 4:35 PM + 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. + To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. Abstract This memo defines a new DHCP option for selecting the subnet on which to allocate an address. This option would override a DHCP server's - normal methods of selecting which subnet on which to allocate an - address for a client. + normal methods of selecting the subnet on which to allocate an address + for a client. + Waters Expires: Jun 1999 + 6 months [Page 1] Table of Contents 1. Introduction......................................................2 2. Subnet Selection Option...........................................3 3. Intellectual Property.............................................4 4. Acknowledgements..................................................4 5. Security Considerations...........................................4 - 6. References........................................................4 + 6. References........................................................5 7. Editor's Addresses................................................5 8. Full Copyright Statement..........................................5 1. Introduction This memo was produced by the DHCP Working Group and defines a new - DHCP option that specifies the subnet on which a DHCP server should - use when selecting an address. This option takes precedence over - other methods that the DHCP server may use to determine the subnet on - which to select an address. Two existing methods of determining the - subnet on which to select an address are: + DHCP option that specifies the subnet that a DHCP server should use + when selecting an address. This option takes precedence over other + methods that the DHCP server may use to determine the subnet on which + to select an address. Two existing methods of determining the subnet + on which to select an address are: o To use the subnet address of the giaddr field in the DHCP packet, or if the giaddr field is zero; o To use the subnet address of the local interface on which the packet was received by the DHCP server. Methods other than the two described above may exist. - The subnet selection option is useful, but not limited to, the class - of devices that have a packet-handling plane (e.g.: switching, routing - functionality) and a control plane (e.g.: device management and - control functionality). The control plane is network connected and + The subnet selection option is useful for, but not limited to, the + class of devices that have a packet-handling plane (e.g.: switching, + routing functionality) and a control plane (e.g.: device management + and control functionality). The control plane is network connected and there is a DHCP server connected to that network. The packet-handling plane may or may not be network connected, however, in either case there is no network connected DHCP server available to this plane. The control plane is not network connected to the packet-handling plane, although the two planes may communicate using some method (e.g.: an internal data bus). - For the networks to which the packet-handling plane is connected, - there is a requirement to allocate addresses for devices connected to - those networks. + There is a requirement to allocate addresses for devices connected to + the networks to which the packet-handling plane is connected. Since there is no network connectivity between the DHCP server and the packet-handling plane, the control plane must allocate addresses using - the DHCP on behalf of the packet-handling plane. Because the control - plane is requesting the addresses, the DHCP server would normally have - the undesired result of allocating the address on the subnet on which - the control plane is connected. + the DHCP on behalf of the packet-handling plane. Since the control + plane is requesting the address, the DHCP server would normally + + Waters Expires: Jun 1999 + 6 months [Page 2] + allocate the address on the subnet on which the control plane is + connected, which would not be the desired result. If the option specified by this memo is included in the DHCPDISCOVER/DHCPREQUEST message then the server should allocate an address on the subnet or network segment that is specified by this - option. The option would specify an address of one of the packet- + option. The option would specify an address on one of the packet- handling plane's subnets. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Subnet Selection Option The subnet selection option is a DHCP option. The option contains a single IP address that is the address of a subnet. The value for the subnet address is determined by taking any IP address on the subnet and ANDing that address with the subnet mask (i.e.: the network and subnet bits are left alone and the remaining (address) bits are set to - zero). When this option is present, the DHCP server MUST use either - the: + zero). When this option is present, the DHCP server MUST use either: o The subnet specified in the option, or; + o A subnet on the same network segment as the subnet specified in the option; on which to allocate an address. The format of the option is: Code Len IP Address +-----+-----+-----+-----+-----+-----+ | TBD | 4 | A1 | A2 | A3 | A4 | @@ -116,36 +122,42 @@ The format of the option is: Code Len IP Address +-----+-----+-----+-----+-----+-----+ | TBD | 4 | A1 | A2 | A3 | A4 | +-----+-----+-----+-----+-----+-----+ In order to ensure backwards compatibility of clients that do support this option when communicating with DHCP servers that do not support - this option, the DHCP client SHOULD check that an allocated address in + this option, the DHCP client SHOULD check that an allocated address is on the requested subnet or network segment. The client SHOULD NOT respond to a DHCPOFFER or DHCPACK of an address that is not on the requested subnet or network segment. - This option does not require any change to other operations or - features of the DHCP server other than to select the subnet on which - to allocate an address. For example, the handling of DHCPDISCOVER for - an unknown subnet may continue to operate unchanged. + Servers supporting this option MUST return the option to any client + that sends it, regardless of whether or not the client requests it in + a parameter request list. Clients using this option must discard + DHCPOFFER or DHCPACK packets that do not contain this option. + + Waters Expires: Jun 1999 + 6 months [Page 3] + This option does not require changes to operations or features of the + DHCP server other than to select the subnet on which to allocate an + address. For example, the handling of DHCPDISCOVER for an unknown + subnet may continue to operate unchanged. When this option is present and the server supports this option, the server MUST NOT offer an address that is not on the requested subnet or network segment. - Existing methods for determining where to send a reply to a DHCP - client are not changed when this option is present in a request. + The IP address to which a DHCP server sends a reply to MUST be the + same as it would chose when this option is not present. 3. Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards- @@ -159,28 +171,30 @@ The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 4. Acknowledgements This document is the result of work undertaken the by DHCP working - group. Thanks to Tim Aston and Ralph Droms for reviewing this memo. + group. Thanks to Ted Lemon, Tim Aston and Ralph Droms for their + helpful comments in this work. 5. Security Considerations DHCP currently provides no authentication or security mechanisms. Potential exposures to attack are discussed is section 7 of the protocol specification [RFC2131]. + Waters Expires: Jun 1999 + 6 months [Page 4] 6. References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, March 1997. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC2132] Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997. @@ -215,10 +229,12 @@ 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. + + Waters Expires: Jun 1999 + 6 months [Page 5]