Internet Engineering Task Force H. Levkowetz Internet-Draft ipUnplugged Expires: August 23, 2002 February 22, 2002 DHCP Option for Mobile IP Foreign Agents 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 August 23, 2002. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document defines a new Dynamic Host Configuration Protocol (DHCP) option which is passed from the DHCP Server to the DHCP Client to announce the presence of one or more Mobile IP Foreign Agents. For each announced Foreign Agent, information is provided which is the same as that of the Mobile IP Agent Advertisement extension to ICMP Router Advertisements. Levkowetz Expires August 23, 2002 [Page 1] Internet-Draft DHCP Option for Foreign Agents February 2002 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements terminology . . . . . . . . . . . . . . . . . . . . 3 3. Foreign Agent Option Definition . . . . . . . . . . . . . . . . 3 4. Foreign Agent Option Usage . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 8 Levkowetz Expires August 23, 2002 [Page 2] Internet-Draft DHCP Option for Foreign Agents February 2002 1. Introduction There already exists a DHCP option to announce Mobile IP Home Agent addresses, described in RFC 2132 [5]. There is, however, no option available to announce Mobile IP Foreign Agents. Announcement of available Mobile IP Foreign Agents by means of DHCP provides possibilities for selective and individual assignment of Foreign Agents to Mobile Nodes. This in turn makes load-sharing and selective service offerings easier. This draft describes a DHCP option for announcing Foreign Agents to DHCP Clients. 2. Requirements terminology 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]. The Mobile IP related terminology used in this document is described in RFC 3220 [8]. 3. Foreign Agent Option Definition The Foreign Agent DHCP option contains the address of one or more foreign agents, together with all the information about the foreign agent which is normally found in a Mobile IP Agent Advertisement extension to ICMP Router Advertisements as described in RFC 3220 [8]. All fields are defined so as to correspond to fields of the same name in a Mobility Agent Advertisement Extension as described in RFC 3220 [8], and if in the future additional bits are allocated from the 'reserved' field for the Mobility Agent Advertisement Extension, they should be equally valid in a DHCP Foreign Agent option. This option may contain announcements of one or more Mobility Agents, in sequence. Each Mobility Agent announcement will require 8+4N bytes, where N is the number of care-of addresses in the individual mobility agent announcement. The number N may be different for each individual mobility agent announcement. The total lenght is 4 + the aggregated length of the mobility agent announcements, where 4 accounts for the Option code, Length and Reserved-0 fields. Levkowetz Expires August 23, 2002 [Page 3] Internet-Draft DHCP Option for Foreign Agents February 2002 The format of the option is as follows: 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 code | Length | Reserved-0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mobility Agent IP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Adv-Length | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Registration Lifetime |R|B|H|F|M|G|r|T| reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | zero or more care-of addresses | | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | zero or more additional mobility agent announcements | | ... | Option code DHCP_FA_OPTION (to be assigned by IANA) Length Length in bytes of this option, not including the Option code and Length bytes. Agent IP Address The address trough which the Mobile Node may reach the announced Foreign Agent in order to do a Mobile IP registration. Type 16. This is the same value as for the type field in a Mobility Agent Advertisement Extension as described in RFC 3220 [8]. If other Mobility Agent Advertisement Extensions are defined in the future, this field will make it possible to differentiate between them without using new DHCP option numbers. Reserved-0 Sent as zero; ignored on reception. Adv-Length (6 + 4*N), where 6 accounts for the number of bytes in the Sequence Number, Registration Lifetime, flags, and reserved fields, and N is the number of care-of addresses Levkowetz Expires August 23, 2002 [Page 4] Internet-Draft DHCP Option for Foreign Agents February 2002 advertised for the Foreign Agent. Sequence Number The count of Foreign Agent DHCP announcements made since the DHCP server was initialized (RFC 3220, Section 2.3.2 [8]). Registration Lifetime The longest lifetime (measured in seconds) that this agent is willing to accept in any Registration Request. A value of 0xffff indicates infinity. R Registration required. Registration with this foreign agent (or another foreign agent listed in this DHCP option) is required even when using a co-located care-of address. B Busy. The foreign agent will not accept registrations from additional mobile nodes. H Home agent. This agent offers service as a home agent on the link on which this mobility agent announcement is sent. F Foreign agent. This agent offers service as a foreign agent on the link on which this mobility agent announcement is sent. M Minimal encapsulation. This agent implements receiving tunneled datagrams that use minimal encapsulation [2]. G GRE encapsulation. This agent implements receiving tunneled datagrams that use GRE encapsulation [1]. r Sent as zero; ignored on reception. SHOULD NOT be allocated for any other uses. T Foreign agent supports reverse tunneling [7]. reserved Sent as zero; ignored on reception. Care-of Address(es) The foreign agent care-of address(es) provided by this Levkowetz Expires August 23, 2002 [Page 5] Internet-Draft DHCP Option for Foreign Agents February 2002 foreign agent. An DHCP Foreign Agent Announcement MUST include at least one care-of address if the 'F' bit is set. The number of care-of addresses present is determined by the Length field in the Extension. 4. Foreign Agent Option Usage The DHCP Foreign Agent option MAY be used by a DHCP server in DHCPOFFER and DHCPACK messages. It MAY be requested by a DHCP client in the Parameter Request List option, and if so, the DHCP server MAY respond with the Foreign Agent option present. 5. Security Considerations DHCP currently provides no authentication or security mechanisms. Potential exposures to attack are discussed is section 7 of the protocol specification RFC 2131 [4]. Likewise, according to RFC 3220 [8], no authentication is required for Agent Advertisement and Agent Solicitation messages. By providing Agent Advertisements by means of DHCP as an alternative to extended ICMP Router Advertisement messages it is possible to do so more selectively, and it does not offer any new threat to the internet. 6. IANA Considerations The value for the DHCP_FA_OPTION code must be assigned from the numbering space defined for public DHCP Options in RFC 2939 [6]. This must not conflict with any other numbers already allocated in this numbering space. 7. Acknowledgements References [1] Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 1701, October 1994. [2] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, October 1996. [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [4] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, Levkowetz Expires August 23, 2002 [Page 6] Internet-Draft DHCP Option for Foreign Agents February 2002 March 1997. [5] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997. [6] Droms, R., "Procedures and IANA Guidelines for Definition of New DHCP Options and Message Types", BCP 43, RFC 2939, September 2000. [7] Montenegro, G., "Reverse Tunneling for Mobile IP, revised", RFC 3024, January 2001. [8] Perkins, C., "IP Mobility Support for IPv4", RFC 3220, January 2002. Author's Address Henrik Levkowetz ipUnplugged AB Arenavagen 33 Stockholm S-121 28 SWEDEN Phone: +46 8 725 9513 EMail: henrik@levkowetz.com Levkowetz Expires August 23, 2002 [Page 7] Internet-Draft DHCP Option for Foreign Agents February 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. 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