Internet Area L.Huang Internet Draft China Mobile Intended status: Informational X.Cheng&L.Lin Expires: September 2, 2009 BUPT March 2, 2009 Extension of DHCP Relay Agent Information Option draft-huang-dhcp-su-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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 September 2, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Huang&Cheng&Lin Expires September 2, 2009 [Page 1] Internet-Draft DHCP Option Extension February 2009 Abstract This Internet draft describes an extension of DHCP Relay Agent Information option for the IP address assignment diversity and the server-to-client replies forwarding convenience. Table of Contents 1. Introduction................................................2 2. Extension of DHCP Relay Agent Information Option.............2 2.1. Purpose................................................3 2.2. Mechanism..............................................3 3. Security Considerations......................................5 4. IANA Considerations.........................................5 5. References..................................................5 Author's Addresses.............................................6 1. Introduction As defined in RFC 3046, Relay Agent Information option is inserted by the DHCP relay agent (or downstream network element) when forwarding client-originated DHCP packets to a DHCP server. Servers recognizing the Relay Agent Information option may use the information to implement IP address or other parameter assignment policies. The DHCP Server echoes the option back verbatim to the relay agent in server- to-client replies, and the relay agent strips the option before forwarding the reply to the client. How to implement more flexible IP address assignment policies with the Relay Agent Information option? This document define an extension of DHCP Relay Agent Information option for the IP address assignment diversity and the server-to-client replies forwarding convenience. 2. Extension of DHCP Relay Agent Information Option Huang&Cheng&Lin Expires September 2, 2009 [Page 2] Internet-Draft DHCP Option Extension February 2009 2.1. Purpose According to RFC 3046, Relay Agent Information Option is mainly responsible for: (1) More flexible IP address assignment policies; (2) More better server-to-client replies forwarding. Does Relay Agent Information option gain its ends? DHCP Server may implement IP address assignment policies with the circuit information carried in Relay Agent Information option. However, such information isn't legible enough. Inserted more earlier, the Relay Agent Information option is more specific. But the option can't precisely locate the client even it's inserted in the device closest to the client. Although Relay Agent Information option can be used to relay DHCP responses back to the proper circuit, this only works in the network element which inserts the option. As the result, the circuit information in Relay Agent Information option can't fully support the IP address assignment policies. What the DHCP server needs is to locate the client level by level with the whole path information form client to server. Its benefit is that IP address assignment policies of different granularities can be made. When transmitting the server-to-client replies, all network elements can make use of the Relay Agent Information option. 2.2. Mechanism The "Relay Agent Information" option is organized as a single DHCP option that contains one or more "sub-options" that convey information known by the relay agent. The initial sub-options are defined for a relay agent that is co-located in a public circuit access unit. The Agent Information field consists of a sequence of SubOpt/Length/Value tuples for each sub-option. Such definition in RFC 3046 has some drawbacks: (1) Relay Agent Information option can only be added by one device in the network, other network elements can only forward the message when finding Relay Agent Information option in it. (2) Sub-option is used to define a kind of information, which means sub-options of the same type value can't coexist in one Relay Agent Information option. Huang&Cheng&Lin Expires September 2, 2009 [Page 3] Internet-Draft DHCP Option Extension February 2009 Based on the demand of the new Relay Agent Information option, we extend this option as following: There is still unique Relay Agent Information option in a DHCP message, but this option can be modified by multiple network elements between DHCP client and DHCP server. For the sake of distinguishing the information added by different devices, we define a new sub- option whose type field is y and len field is 0, which are used to identify the end of modification of one device. When a network element receives a DHCP message, if it wants to add Relay Agent Information option, it must check whether Relay Agent Information is already existed in current message. If there is no Relay Agent Information option in the message, the network element adds this kind of option according to RFC 3046; otherwise, the network element adds a new option information after existed option in the sub-options form that are defined in RFC 3046 or other RFCs, such as sub- option1(circuit) and sub-option2(remote). Regardless of the two situations, devices must plus a sub-option(type x, len 0) that is defined above to indicate the end of the modification and increase corresponding number in length field of Relay Agent Information option. For example, if all network elements add sub-option1 and sub-option2, DHCP Relay Agent Information option may be following format: Relay Agent Information option: +-------+------+-----+ |Code(x)|Len(N)|Value| +-------+------+-----+ Value: +---+----+--------+---+----+--------+---+---+ | 1 | N1 | a1~aN1 | 2 | N2 | b1~bN2 | y | 0 | +---+----+--------+---+----+--------+---+---+ | 1 | N3 | c1~cN3 | 2 | N4 | d1~dN4 | y | 0 | +---+----+--------+---+----+--------+---+---+ / ... \ Huang&Cheng&Lin Expires September 2, 2009 [Page 4] Internet-Draft DHCP Option Extension February 2009 \ ... / +---+----+--------+---+----+--------+---+---+ | 1 | N51| y1~yN3 | 2 | N52| z1~zN52| y | 0 | +---+----+--------+---+----+--------+---+---+ DHCP server receiving the DHCP message can obtain layer Relay Agent Information option information and it can allocate different IP address according to the different strategy of allocating granularity constituted by option. Then, Relay Agent Information option is replicated in DHCP response to the DHCP client. Network elements (e.g.: DHCP relay agent or downstream network element) strip its own sub-options when receiving the DHCP response packets and then relay DHCP responses back to the proper circuit by reading the sub-options. 3. Security Considerations This document doesn't propose any new protocol. 4. IANA Considerations This document requires a new number for DHCP option code x and a new DHCP sub-option code y described in section 2.2. 5. References [RFC2131] R. Droms, Bucknell University, " Dynamic Host Configuration Protocol ", RFC 2131, March 1997. [RFC2132] S. Alexander, Silicon Graphics, Inc., and R. Droms, " DHCP Options and BOOTP Vendor Extensions ", RFC 2132, March 1997. Huang&Cheng&Lin Expires September 2, 2009 [Page 5] Internet-Draft DHCP Option Extension February 2009 [RFC3046] M. Patrick, Motorola BCS, " DHCP Relay Agent Information Option ", RFC 3046, January 2001. Author's Addresses Lu Huang China Mobile 53A,Xibianmennei Ave., Xuanwu District, Beijing 100053 China Email: huanglu@chinamobile.com Xu Cheng Beijing University of Posts and Telecommunications 10,Xitucheng Road., Haidian District, Beijing 100876 China Email: chengx@buptnet.edu.cn Lin Lin Beijing University of Posts and Telecommunications 10,Xitucheng Road., Haidian District, Beijing 100876 China Email: linl@buptnet.edu.cn Huang&Cheng&Lin Expires September 2, 2009 [Page 6]