Network Working Group R. Johnson Internet-Draft J. Jumarasamy Expires:
December 31, 2005April 24, 2006 K. Kinnear M. Stapp Cisco Systems, Inc. June 29,October 21, 2005 DHCP Server-IDServer Identifier Override Suboption draft-ietf-dhc-server-override-02.txtdraft-ietf-dhc-server-override-03.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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 December 31, 2005.April 24, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This memo defines a new suboption of the DHCP relay information option which allows the DHCP relay to specify a new value for the Server-IDServer Identifier option, which is inserted by the DHCP Server. In some cases it is convenient forThis allows the DHCP relay to act as the actual DHCP server such that DHCP RENEWAL requestsRENEW DHCPREQUESTs will come to the relay instead of going to the server directly. This gives the relay the opportunity to include the Relay Agent option with appropriate suboptions even on RENEWALDHCP RENEW messages. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .3 2. Server-ID Override Suboption DefinitionConventions . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Server Identifier Override Suboption Definition . . . . . . 5 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 4.6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5.7 6. Intellectual Property Rights and Copyright . . . . . . . . . . 7 6.8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 89 Intellectual Property and Copyright Statements . . . . . . . . 910 1. Introduction There are many situations where the DHCP relay is involved and can insert a relay agent option with appropriate suboptions easily into DHCP DISCOVER messages. Once the lease has been granted, however, future DHCP RENEWAL messages are sent directly to the DHCP Server as specified in the Server-IDServer Identifier option. This means that the relay may not see the DHCP RENEWAL messages (depending upon network topology) and thus can not provide the same relay agent option information in the RENEWAL messages. This new DHCP relay agent suboption, Server-IDServer Identifier override, allows the relay to tell the DHCP server what value to place into the Server-IDServer Identifier option. Using this, the relay agent can force RENEWAL messages to come to it instead of the server. The relay may then insert the relay agent option with appropriate suboptions and relay the requestDHCPREQUEST to the actual server. In this fashion the DHCP server will be provided with the same relay agent information upon renewals (such as Circuit-ID, Remote-ID, Device Class, etc.) as was provided in the initial DISCOVER message. In effect, this makes a RENEWAL into a REBINDING. This new suboption could also be used by the DHCP relay in order to allow the relay to appear as the actual DHCP server to the client. This has the advantage that the relay can more easily keep up-to-date information about leases granted, etc. In short, this new suboption allows the DHCPv4 relay to function in the same fashion as the DHCPv6 relay currently does. 2. Server-IDConventions 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 RFC 2119 . 3. Server Identifier Override Suboption Definition The format of the suboption is: Code Len Overriding Server-IDServer Identifier address +-----+-----+-----+-----+-----+-----+ | TBD | n | a1 | a2 | a3 | a4 | +-----+-----+-----+-----+-----+-----+ Figure 1 The option length (n) is 4. The octets "a1" through "a4" specify the value which SHOULDMUST be inserted into the Server-IDServer Identifier option by the DHCP Server upon reply. DHCP Servers SHOULDwhich implement this Relay Suboption MUST use this value, if present, as the value to insert into the Server-IDServer Identifier option whenever responding to a DHCP Client. If a DHCP Server does not understand/implement this Relay Suboption, it will ignore the Suboption, and thus will insert it's own appropriate interface address as the Server Identifier address. In this case, the DHCP Relay will not receive RENEW DHCPREQUEST packets from the client. When servicingconfiguring a DHCP REQUESTRelay to use this Suboption, the administrator of the Relay should take into account whether or not the DHCP Server to which the packet will be relayed will correctly understand this Suboption. When servicing a DHCPREQUEST packet the DHCP Server would normally look at the Server-IDServer Identifier option for verification that the address specified there is one of the addresses associated with the DHCP Server, silently ignoring the REQUESTDHCPREQUEST if it does not match a configured DHCP Server interface address. If the REQUESTDHCPREQUEST packet contains a Server-IDServer Identifier Override Suboption, however, comparison should be made between this suboption and the Server-IDServer Identifier option. If both of the Server-IDServer Identifier Override Suboption and the Server-IDServer Identifier Option specify the same address, then the Server should accept the REQUESTDHCPREQUEST packet for processing, regardless of whether or not the Server-IDServer Identifier Option matchs a DHCP Server interface. 3.The DHCP Relay should fill in the giaddr field when relaying the packet just as it normally would do. 4. Security Considerations Message authentication in DHCP for intradomain use where the out-of- band exchange of a shared secret is feasible is defined in . Potential exposures to attack are discussed in section 7 of the DHCP protocol specification in . The DHCP Relay Agent option depends on a trusted relationship between the DHCP relay agent and the server, as described in section 5 of RFC 3046. While the introduction of fraudulent relay-agent options can be prevented by a perimeter defense that blocks these options unless the relay agent is trusted, a deeper defense using the authentication option for relay agent options  SHOULD be deployed as well. If a rogue DHCP relay were inserted between the client and the server, it could redirect clients to it using this suboption. This would allow such a system to later deny renew requestsRENEW DHCPREQUEST and thus force clients to discontinue use of their allocated address. This interception, however, would need to be done during the initial DISCOVER and OFFER phase, since the suboption value SHOULD be ignored by the server during RENEWAL state. Either DHCP Authentication  or DHCP Relay Agent option authentication  would address this case. 4.5. IANA Considerations IANA is requested to assign a suboption number for the Server Identifier Override Suboption from the DHCP Relay Agent Information Option  suboption number space. None. 5.6. Intellectual Property Rights and Copyright The IETF has been notified of intellectual property rights claimed in regard to some or all of the specification contained in this document. For more information consult the online list of claimed rights. Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights." This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. 6.7. References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, March 1997.  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  Droms, R., "Authentication for DHCP Messages", RFC 3118, June 2001.  Stapp, M., "The Authentication Suboption for the DHCP Relay Agent Option", RFC 4030, March 2005.  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, October 1998.  Patrick, M., "DHCP Relay Agent Information Option", RFC 3096,3046, November 2004. Authors' Addresses Richard A. Johnson Cisco Systems, Inc. 170 W. Tasman Dr. San Jose, CA 95134 US Phone: +1 408 526 4000 Email: email@example.com Jay Kumarasamy Cisco Systems, Inc. 170 W. Tasman Dr. San Jose, CA 95134 US Phone: +1 408 526 4000 Email: firstname.lastname@example.org Kim Kinnear Cisco Systems, Inc. 170 W. Tasman Dr. San Jose, CA 95134 US Phone: +1 408 526 4000 Email: email@example.com Mark Stapp Cisco Systems, Inc. 170 W. Tasman Dr. San Jose, CA 95134 US Phone: +1 408 526 4000 Email: firstname.lastname@example.org Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights 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; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at email@example.com. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society.