Network Working Group Y. Cui Internet-Draft P. Wu Intended status: Standards Track J. Wu Expires: June 2, 2012 Tsinghua University T. Lemon Nominum, Inc. November 30, 2011 DHCPv4 over IPv6 Transport draft-ietf-dhc-dhcpv4-over-ipv6-00 Abstract Recently, there are demands arising for IPv4 address allocation under IPv6 environment, especially in IPv6 transition scenarios. This document describes the mechanism to survive DHCPv4 over IPv6 network. DHCPv4 messages are transported in IPv6 packets when traversing the IPv6 network. DHCPv4 protocol behavior of the client and server is extended to support this IPv6 transport. For the relay case, a new suboption of the Relay Agent Information Option is defined to carry the remote IPv6 address of the clients. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on June 2, 2012. Copyright Notice Copyright (c) 2011 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 Cui, et al. Expires June 2, 2012 [Page 1] Internet-Draft DHCPv4 over IPv6 November 2011 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Protocol Summary . . . . . . . . . . . . . . . . . . . . . . . 4 5. Client Relay Agent IPv6 Address Sub-option . . . . . . . . . . 6 6. Client Relay Agent Behavior . . . . . . . . . . . . . . . . . . 6 7. IPv6-Transport Server Behavior . . . . . . . . . . . . . . . . 7 8. IPv6-Transport Relay Agent Behavior . . . . . . . . . . . . . . 7 9. Security Consideration . . . . . . . . . . . . . . . . . . . . 8 10. IANA consideration . . . . . . . . . . . . . . . . . . . . . . 8 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 11.1. Normative References . . . . . . . . . . . . . . . . . . . 8 11.2. Informative References . . . . . . . . . . . . . . . . . . 8 Cui, et al. Expires June 2, 2012 [Page 2] Internet-Draft DHCPv4 over IPv6 November 2011 1. Introduction DHCPv4 [RFC2131] was not designed with IPv6 consideration. In particular, DHCPv4 cannot work on the IPv6 network. However, with IPv4-IPv6 coexistence coming to reality, the demand of allocating IPv4 address under IPv6 environment naturally arises. To meet this demand, DHCPv4 should be extended to run over the IPv6 network. A typical scenario that probably requires this feature is IPv4-over- IPv6 hub and spoke tunnel [RFC4925]. In this scenario, IPv4-over- IPv6 tunnel is used to provide IPv4 connectivity to end users (hosts or end networks) across an IPv6 network. If the IPv4 addresses of the end users are provisioned by the concentrator side, then the provisioning process should be able to cross the IPv6 network, too. One such tunnel mechanism is demonstrated in [I-D.ietf-softwire-public-4over6]. DHCPv4 over IPv6 would be a generic solution for this scenario. Three main flavours of solutions may be considered: o Use DHCPv6 instead of DHCPv4, to provision IPv4-related connectivity. In DHCPv6, the provisioned IPv4 address can be embedded into IPv6 address, or carried within a new option. Along with that, dedicated options are needed to convey IPv4-related information, such as the IPv4 address of DNS server, NTP server, etc. Therefore it will put a certain amount of IPv6-unrelated information into DHCPv6 protocol. o Use DHCPv4 and tunnel DHCPv4-in-IPv4 packets over IPv6. Unlike the previous approach where DHCPv6 is used for both IPv4 and IPv6 connectivity, this approach consists in preserving the separation between IPv4 and IPv6 connectivity information. It allows to maintain the IPv4 service without major modification of IPv6- related provisioning resources, and sustains DHCPv4 to be the IPv4-related information carrier. However, this approach enforces an IPv4-in-IPv6 tunnel onto DHCP, and requires extra efforts to maintain tunnel endpoint information for encapsulation use. o Use DHCPv4 and extend it to work over IPv6 transport. This flavour uses IPv6 directly for DHCP packet transport instead of relying on IPv4-in-IPv6 tunnel, and it keeps the advantage of separation with IPv6 connectivity information. This document focuses on this flavour. The document will define the extensions of DHCPv4 protocol behavior, as well as a new suboption of the Relay Agent Information Option, to fully support DHCPv4 over IPv6. 2. Requirements Language Cui, et al. Expires June 2, 2012 [Page 3] Internet-Draft DHCPv4 over IPv6 November 2011 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]. 3. Terminology This document makes use of the following terms: o DHCPv4: IPv4 Dynamic Host Configuration Protocol [RFC2131]. o Client Relay Agent(CRA): a special DHCPv4 Relay Agent that sits on the same, IPv6-accessable host with the DHCPv4 client. CRA works as a "bridge" between DHCPv4 client and the IPv6 network, to convert between IPv4 transport and IPv6 transport. o IPv6-Transport Server(TSV): a DHCPv4 Server that support supports IPv6 transport. TSV can listen on IPv6 for incoming DHCPv4 messages, and send DHCPv4 messages in IPv6 packets. o IPv6-Transport Relay Agent(TRA): a DHCPv4 Relay Agent that supports IPv6 transport. TRA sits on a machine which has both IPv6 and IPv4 connectivity, and relays DHCP packets between CRA and normal DHCPv4 server. o Client Relay Agent IPv6 Address Sub-option(6ADDR suboption): a new suboption of DHCP Relay Agent Information Option [RFC3046] defined in this document. 6ADDR suboption is used by TRA to carry the IPv6 address of a CRA. 4. Protocol Summary The scenario for DHCPv4 over IPv6 transport is shown in Figure 1. DHCPv4 clients and DHCPv4 server/relay are separated by an IPv6 network in the middle. DHCP messages between a client and the server/relay cannot naturally be forwarded to each other because they are by default IPv4 UDP packets, either unicast or broadcast. To bridge this gap, both the client side and the server/relay side should enable DHCPv4 over IPv6 transport. To be more precise, they shoudl support delivering and receiving DHCP messages in IPv6 UDP packets and thereby traverse the IPv6 network. On the client side, a special relay agent called Client Relay Agent is placed on the same machine with the client. CRA is used to relay DHCP messages from the client to the server, and from the server to the client. CRA sends DHCPv4 messages to the server through unicast IPv6 UDP, and receives unicast IPv6 UDP packets with the DHCPv4 messages from the server. By using CRA, no extension is required on the DHCP client. Cui, et al. Expires June 2, 2012 [Page 4] Internet-Draft DHCPv4 over IPv6 November 2011 +-------------------------+ +------+ | |DHCPv4| | |Client| +-------+ +------+ |DHCPv4 | | IPv6 Network |Server/| +------+ |Relay | |DHCPv4| +-------+ |Client| | +------+ | +-------------------------+ Figure 1 Scenario of DHCPv4 over IPv6 Transport The IPv6-Transport DHCPv4 server can receive DHCP messages delivered in IPv6 UDP from CRA, and send out DHCP messages to CRA using IPv6 UDP(figure 2(a)). TSV should send DHCP messages to the IPv6 address from which it receives relevant DHCP messages earlier. When CRAs communicate with an IPv6-Transport Relay Agent rather than with a server directly, the situation will become a little more complicated. Besides the IPv6 communication with CRA, TRA also communicates with a regular DHCPv4 server through IPv4. Therefore, when TRA relays DHCP messages between a CRA and the DHCPv4 server, it receives DHCP message from the CRA in IPv6 and sends it to the server in IPv4, while receives DHCP message from the server in IPv4 and sends it to the CRA in IPv6. TRA has to use the DHCP Relay Agent Information Option(Option 82) to record the IPv6 address of a CRA, which will be used as forwarding destination when relaying DHCP a message from the server. Since Option 82 doesn't has an existing suboption that fits in the case, this document defines a new Client Relay Agent IPv6 Address Sub-option. +------+ +------+ |client| IPv6 network |TSV | |+CRA |----------------| | +------+ +------+ (a)client--server case +------+ +------+ +------+ |client| IPv6 network |TRA | IPv4 network |server| |+CRA |----------------| |--------------| | +------+ +------+ +------+ (b)client--relay--server case Cui, et al. Expires June 2, 2012 [Page 5] Internet-Draft DHCPv4 over IPv6 November 2011 Figure 2 Protocol Summary 5. Client Relay Agent IPv6 Address Sub-option This suboption MUST be added by a DHCPv4 TRA. It encodes the IPv6 address of the host from which a DHCPv4-in-IPv6 CRA-to-TRA packet was received. It is intended for the TRA to relay DHCPv4 replies back to the proper CRA. To be more specific, the TRA uses the IPv6 address encoded in this suboption as the destination IPv6 address when relaying a DHCPv4 reply to IPv6 network. The CRA IPv6 address MUST be unique in the IPv6 domain. The 6ADDR suboption has a fixed length of 18 octets. The SubOpt code is tbd by IANA, the length field should be 16, and the following 16 octets contain the CRA IPv6 address. DHCP servers MAY use this suboption to select parameters specific to particular hosts. Servers MAY parse this suboption and extract the semantic of IPv6 address. SubOpt Len Agent Remote ID +------+------+------+------+------+- -+------+ | tbd | 16 | a1 | a2 | a3 | ... | a16 | +------+------+------+------+------+- -+------+ Figure 3 Client Relay Agent IPv6 Address Sub-option format 6. Client Relay Agent Behavior A Client Relay Agent sits on the same machine with the DHCPv4 client. CRA is a special type of relay agent, which relays DHCPv4 messages between regular client and TSV/TRA. The communication between CRA and the client happens within the machine using IPv4, and the communication between CRA and TSV/TRA happens on the IPv6 network using IPv6. A CRA is configured with one or more IPv6 addresses of TSV/TRA. This configuration is provided before DHCPv4 process, for example through DHCPv6 option, or by some other mechanisms depending on the application scenarios. A CRA listens for DHCP packets on IPv4 UDP port 67. When it receives from IPv4 any DHCP packet with bootp op field = 1, it forwards the packet using the standard DHCP relay agent format, but over UDPv6, with source port 67 and destination port 67. Here the CRA MUST NOT Cui, et al. Expires June 2, 2012 [Page 6] Internet-Draft DHCPv4 over IPv6 November 2011 include an option 82 or modify the giaddr field of the DHCP packet. The CRA forwards the packet to each of the DHCP server or relay agent with which it is configured. The CRA MUST use a global IPv6 address if it has one. A CRA also listens for DHCP packets on IPv6 UDP port 68. When it receives from IPv6 any DHCP packet with bootp op field = 2, the CRA checks to see if the packet contains option 82, and if so, it drops the packet. Otherwise, it delivers the packet to the DHCP client using IPv4. 7. IPv6-Transport Server Behavior To support IPv6 transport, the behavior of DHCPv4 server should be extended. The IPv6-Transport Server can listen on IPv6 port 67 for DHCPv4 packets, and send DHCPv4 packets through IPv6. A TSV listens for DHCP packets on IPv6 UDP port 67. When it receives from IPv6 a DHCP packet, it MUST record the IPv6 source address of that packet and retain it as the return address of the packet. That is to say, when sometime later the TSV responds to this packet, it MUST send the reply packet to the IPv6 return address retained earlier. The rest of TSV DHCP process is the same with normal DHCPv4 server. A TSV can also listen on IPv4 UDP port 67 like a normal DHCPv4 server, and process normally when receives IPv4 DHCPv4 packet. This document places no new requirements on DHCPv4 servers that do not listen on UDPv6--in order to use an IPv4-only DHCPv4 server through an IPv6 connection, a TRA is required. 8. IPv6-Transport Relay Agent Behavior An IPv6-Transport Relay Agent sits between IPv6 network and IPv4 network, and relays DHCPv4 message between CRAs and IPv4-only DHCPv4 server. The communication between CRAs and the TRA uses IPv6, while the communication between TRA and server uses IPv4. A TRA listens on IPv6 UDP port 67 for DHCP packets with bootp op field = 1, as well as IPv4 UDP port 68 for DHCP packets with bootp op field = 2. When relaying a DHCP message from CRA to server, TRA MUST add an option 82 with a 6ADDR suboption. This suboption contains the IPv6 source address of the message (the CRA's IPv6 address) which is retained when the message is received in IPv6. The TRA MUST also store the IPv4 address of itself in the giaddr field of the DHCP message. The TRA MAY include a Link Selection Suboption [RFC3527] to indicate to the DHCP server which link to use when choosing an IP address. Cui, et al. Expires June 2, 2012 [Page 7] Internet-Draft DHCPv4 over IPv6 November 2011 When a TRA receives a DHCP message from the DHCP server, if the packet contains no 6ADDR suboption, the TRA discards the packet. Otherwise, it processes it as required by [RFC3046], and forwards it to the IPv6 address recorded in the 6ADDR suboption. 9. Security Consideration This specification raises no particular security issues to the DHCPv4 protocol model. 10. IANA consideration IANA is requested to assign one new suboption code from the registry of DHCP Agent Sub-Option Codes maintained in http://www.iana.org/assignments/bootp-dhcp-parameters. This suboption code will be assigned to the Client Relay Agent IPv6 Address Sub-option. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046, January 2001. [RFC3527] Kinnear, K., Stapp, M., Johnson, R., and J. Kumarasamy, "Link Selection sub-option for the Relay Agent Information Option for DHCPv4", RFC 3527, April 2003. [RFC4925] Li, X., Dawkins, S., Ward, D., and A. Durand, "Softwire Problem Statement", RFC 4925, July 2007. 11.2. Informative References [I-D.ietf-softwire-public-4over6] Cui, Y., Wu, J., Wu, P., Metz, C., Cui, et al. Expires June 2, 2012 [Page 8] Internet-Draft DHCPv4 over IPv6 November 2011 Vautrin, O., and Y. Lee, "Public IPv4 over Access IPv6 Network", dr aft-ietf-softwire-public-4over6-00 (work in progress), September 2011. Authors' Addresses Yong Cui Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 P.R.China Phone: +86-10-6260-3059 EMail: cuiyong@tsinghua.edu.cn Peng Wu Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 P.R.China Phone: +86-10-6278-5822 EMail: peng-wu@foxmail.com Jianping Wu Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 P.R.China Phone: +86-10-6278-5983 EMail: jianping@cernet.edu.cn Ted Lemon Nominum, Inc. 2000 Seaport Blvd Redwood City 94063 USA Phone: +1-650-381-6000 EMail: mellon@nominum.com Cui, et al. Expires June 2, 2012 [Page 9]