Dynamic Host Configuration (DHC) G. Ren Internet-Draft L. He Intended status: Informational Y. Liu Expires: September 11, 2019 Tsinghua University March 10, 2019 Problem Statement of Multi-requirement Extensions for Dynamic Host Configuration Protocol for IPv6 (DHCPv6) draft-ren-dhc-problem-statement-of-mredhcpv6-01 Abstract The manageability, security, privacy protection, and traceability of networks can be supported by extending DHCPv6 protocol. This document analyzes current extension practices and typical DHCP server software on extensions, defines a DHCP general model, discusses some extension points, and present extension cases. 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 September 11, 2019. Copyright Notice Copyright (c) 2019 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. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Ren, et al. Expires September 11, 2019 [Page 1] Internet-Draft problem statement of mredhcpv6 March 2019 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Current Extension Practices . . . . . . . . . . . . . . . . . 4 3.1. Standardized and Non-standardized DHCPv6 Extension Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Current DHCPv6 Server Software Cases . . . . . . . . . . . 4 3.2.1. Cisco Prime Network Registrar DHCP Server Extension APIs . . . . . . . . . . . . . . . . . . . . 4 3.2.2. Kea DHCP Hook Mechanisms . . . . . . . . . . . . . . . 5 4. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5 4.1. DHCP General Model . . . . . . . . . . . . . . . . . . . . 5 4.2. Extension Discussion . . . . . . . . . . . . . . . . . . . 6 4.2.1. DHCP Messages . . . . . . . . . . . . . . . . . . . . 6 4.2.2. Options . . . . . . . . . . . . . . . . . . . . . . . 6 4.2.3. Message Processing Functions . . . . . . . . . . . . . 7 4.2.4. Address Generation Mechanisms . . . . . . . . . . . . 7 4.2.5. Extension Principles . . . . . . . . . . . . . . . . . 7 5. Extensions Cases . . . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 9. Normative References . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Ren, et al. Expires September 11, 2019 [Page 2] Internet-Draft problem statement of mredhcpv6 March 2019 1. Introduction The IP address plays a significant role in the communication of the Internet. IP address generation is also closely related to the manageability, security, privacy protection, and traceability of networks. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [I-D.ietf-dhc-rfc3315bis] is an important network protocol that can be used to dynamically provide IPv6 addresses and other network configuration parameters to IPv6 hosts. Actually, DHCPv6 continues to be extended and improved through new options, protocols or message processing mechanisms. Although DHCPv6 provides more and more comprehensive functionality and DHCPv6 server software also provides extension interfaces to allow administrators to alter and customize the way how they handle and respond to DHCPv6 messages, there is still a lack of a general insight into where and how to conduct extensions in DHCPv6 effectively. Therefore, a detailed analysis is required to clarify the problems, design principles, and extract and unify the design specifications to help better solve the extension problems. In summary, multiple extensions on DHCPv6 can be conducted to support the administrator's self-defined functionalities. As DHCPv6 is an important and useful protocol related to IPv6 addresses generation, it can provide more extended and flexible functionalities to meet administrators' requirements. According to well-designed principles, extended interfaces can be defined to support more self-defined multi-requirement extensions without sacrificing the stability of DHCPv6. Some people would suggest administrators modify the open-source DHCP servers to solve their problems. However, a great amount of time will be taken to understand the open source DHCP server codes, not to say the consuming time debugging the bugs, failures or system crash caused by modifying the complicated modules. Another problem is that as the open source software evolves, the source codes of the server software may change (new functionalities or fixing bugs). Users may need to re-write their codes once the new version of open-source server software comes out [kea_dhcp_hook_developers_guide] . Hence, the multi-requirement extensions for DHCPv6 to solve administrators' specific problems are very necessary and significant. This document describes current extension practices and typical DHCP server software on extensions and provides a problem statement by defining a DHCP general model, discussing the extension problems, and presenting extension cases. Ren, et al. Expires September 11, 2019 [Page 3] Internet-Draft problem statement of mredhcpv6 March 2019 2. Terminology Familiarity with DHCPv6 and its terminology, as defined in [I-D.ietf-dhc-rfc3315bis], is assumed. 3. Current Extension Practices 3.1. Standardized and Non-standardized DHCPv6 Extension Cases Many documents attempt to extend DHCPv6. They can be classified into three categories. Extended options Most extensions for DHCPv6 are implemented in this way. New-defined options carry specific parameters in the DHCPv6 messages, which helps DHCPv6 clients or servers know the detailed situation with each other. Extended messages Some documents define new protocols that aim to achieve specific goals, e.g., active leasequery [RFC7653], GAGMS [GAGMS]. Extended entities Some documents introduce third-party entities into the communications of DHCPv6 to achieve specific goals, e.g., authentication [RFC7037]. 3.2. Current DHCPv6 Server Software Cases A lot of commercial and open source DHCP servers exist, including Cisco Prime Network Registrar [CPNR], Microsoft DHCP [Microsoft_DHCP], VitalQIP [VitalQIP], Nominum DHCP [Nominum_DHCP], ISC DHCP [ISC_DHCP], Kea DHCP [Kea_DHCP], FreeRADIUS DHCP [FreeRADIUS_DHCP], WIDE DHCPv6 [WIDE_DHCPv6], and DHCP Broadband [DHCP_Broadband]. Commercial and open source DHCPv6 software often considers the extensions of DHCPv6 servers because they cannot always meet the requirements that the administrators want. In this section, we introduce two typical DHCPv6 servers: Cisco Prime Network Registrar and Kea DHCP. 3.2.1. Cisco Prime Network Registrar DHCP Server Extension APIs Cisco Prime Network Registrar (CPNR) [CPNR] is an appliance which provides integrated Domain Name Server, DHCP, and IP Address Management services for IPv4 and IPv6. At the same time, CPNR DHCP server allows administrators to write extensions and functions to alter and customize how it handles and responds to DHCP requests. A network operator usually decides what packet process to modify, how Ren, et al. Expires September 11, 2019 [Page 4] Internet-Draft problem statement of mredhcpv6 March 2019 to modify, and which extension point to attach the extension. Then the network operator just writes the extension and adds the well- written extension to the extension point of the DHCP server. Finally, the network operator reloads the DHCP server and debugs whether the server runs as it expects. 3.2.2. Kea DHCP Hook Mechanisms Kea DHCP provides hook mechanisms, a well-designed interface for third-party code, to solve the problem that the DHCP server does not quite do what a network operator require. A network operator can use several well-defined framework functions to load and initialize a library and write specific callout functions to attach to the hook points. After building and configuring the hooks library, the server runs as the network operator requires. Additionally, Kea DHCP allows the network operator to use logging in the hooks library. 4. Problem Statement This section elaborates the problem statement of multi-requirement extensions for DHCPv6. Section 4.1 describes the general model of DHCP, while Section 4.2 analyzes the extension points and requirements, suggesting possible future work. 4.1. DHCP General Model Figure 1 summarizes the DHCP general model and its possible extensions: DHCP messages, options, message processing functions, and address generation mechanisms. Ren, et al. Expires September 11, 2019 [Page 5] Internet-Draft problem statement of mredhcpv6 March 2019 +-------------------+ +-------------------+ | DHCPv6 client | | DHCPv6 relay | | +---------------+ | DHCP messages with options| +---------------+ | | | Message | |<------------------------->| | Message | | | | processing | | | | processing | | | | functions | | | | functions | | | +---------------+ | | +---------------+ | +-------------------+ +-------------------+ ^ | DHCP messages with options | | V +-------------------+ | DHCPv6 server | +------------+ | +---------------+ | | Address | | | Message | | | generation |<-----------------------------+-| processing | | | mechanisms | | | functions | | +------------+ | +---------------+ | +-------------------+ Figure 1: DHCP general model and its possible extensions. 4.2. Extension Discussion 4.2.1. DHCP Messages In fact, new messages can be designed and added to DHCPv6 protocol, e.g., active leasequery. But currently, people are always concerned about the security and privacy issues of DHCP protocol. [RFC7819] and [RFC7824] describe the privacy issues associated with the use of DHCPv4 and DHCPv6, respectively. DHCPv6 does not provide the privacy protection on messages and options. That is to say, other nodes can see the options transmitted in the DHCPv6 messages between DHCPv6 clients and servers. 4.2.2. Options DHCPv6 allows defining options for common requirements, e.g., DNS and NTP. In other cases, network operators may require DHCP messages to transmit some self-defined options between clients and servers. Currently, vendor-specific information option allows clients and servers to exchange vendor-specific information. Therefore, administrative domains can define and use sub-options of vendor- specific option to serve their private purposes. However, the content of the self-defined options may come from two sources: hosts and users. If the content of self-defined options comes from the Ren, et al. Expires September 11, 2019 [Page 6] Internet-Draft problem statement of mredhcpv6 March 2019 user, two methods can be used to solve the problem. The first one is that the clients provide related interfaces to receive such information, which is currently merely supported. The second one is that DHCPv6 relays obtain such information and add it into the client's request. But this always depends on other protocols to get the information first. 4.2.3. Message Processing Functions Although current commercial or open-source DHCP server software provide comprehensive functionality, they still cannot meet all customers' requirements of processing DHCP requests. Therefore, improved commercial or open-source DHCP server software will provide interfaces that customers can use to write their specific extensions to affect the way how DHCP servers handle and respond to DHCP requests. For example, not all networks prefer to use DHCPv6 servers to assign the privacy-preserving random-form addresses generated by some fixed address generation mechanism to DHCPv6 clients. Several address generation mechanisms for SLAAC [RFC4862] (e.g., IEEE 64-bit EUI-64 [RFC2464], Constant, semantically opaque [Microsoft], Temporary [RFC4941], and Stable, semantically opaque [RFC7217]) proposed for different requirements can be also utilized in DHCPv6 protocol. The many types of IPv6 address generation mechanisms available have brought about flexibility and diversity. Thus, network operators may alter their DHCPv6 servers through the given extensions to use their own preferred address generation mechanisms to assign addresses to DHCPv6 clients. However, not all DHCP software consider this extension. 4.2.4. Address Generation Mechanisms Currently, DHCPv6 servers try to generate random addresses and assign them to clients. However, different networks may prefer different address generation mechanisms. Corresponding interfaces could be open and defined to allow other address generation mechanisms to be configured. 4.2.5. Extension Principles The principles used to conduct multi-requirement extensions for DHCPv6 are summarized as follows: 1) Do not change the current DHCP general model. 2) Use simpler interfaces to define and support more extensions. 3) TBD Ren, et al. Expires September 11, 2019 [Page 7] Internet-Draft problem statement of mredhcpv6 March 2019 5. Extensions Cases Some administrative domains or countries may have control of out-of- domain resources, and one method to loose the control is that the administrative domains or countries can account for their users using source addresses. Considering such a requirement that DHCP servers assign IP addresses generated by user identifiers to the clients in a network, two extensions should be fulfilled to meet this requirement. The first one is that clients send their user identifiers to servers. This can be achieved by defining and using sub-options of vendor specific information option. For example, the network uses 802.1X to authenticate users. The DHCPv6 relay which can access the user identifiers in the 802.1X authenticator inserts the corresponding user identifier into the client's request. Then DHCPv6 servers can extract user identifier from the request. The second is that servers use user identifiers to generate IP addresses. To achieve this goal, extension mechanisms provided by the server software such as extension points provided by CPNR [CPNR] and hook mechanisms in Kea DHCP [Kea_DHCP] can be used, in which DHCP servers extract user identifiers and generate IP addresses. 6. Security Considerations Security issues related with DHCPv6 are described in Section 22 of [I-D.ietf-dhc-rfc3315bis]. 7. IANA Considerations This document does not include an IANA request. 8. Acknowledgements The authors would like to thank Bernie Volz, Tomek Mrugalski, Sheng Jiang, and Jinmei Tatuya for their comments and suggestions that improved the [draft-ren-dhc-mredhcpv6]. Some ideas and thoughts of [draft-ren-dhc-mredhcpv6] are contained in this document. 9. Normative References [CPNR] Cisco, "Cisco Prime Network Registrar", 2018, . [DHCP_Broadband] Ren, et al. Expires September 11, 2019 [Page 8] Internet-Draft problem statement of mredhcpv6 March 2019 Weird Solutions, "DHCP Broadband", 2018, . [FreeRADIUS_DHCP] FreeRADIUS, "FreeRADIUS DHCP", 2017, . [GAGMS] Liu, Y., He, L., and G. Ren, "GAGMS: A Requirement-Driven General Address Generation and Management System", November 2017. [I-D.ietf-dhc-rfc3315bis] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., Richardson, M., Jiang, S., Lemon, T., and T. Winters, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6) bis", draft-ietf-dhc-rfc3315bis-13 (work in progress), April 2018. [ISC_DHCP] Internet System Consortium, "ISC DHCP", 2018, . [Kea_DHCP] Internet System Consortium, "Kea DHCP", 2018, . [Microsoft] Microsoft, "IPv6 interface identifiers", 2013, . [Microsoft_DHCP] Microsoft, "Microsoft DHCP", 2008, . [NIDTGA] Liu, Y., Ren, G., Wu J., Zhang s., He, L., and Y. Jia, "Building an IPv6 address generation and traceback system with NIDTGA in Address Driven Network", 2015, . [Nominum_DHCP] Nominum, "Nominum DHCP", 2012, . [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet Ren, et al. Expires September 11, 2019 [Page 9] Internet-Draft problem statement of mredhcpv6 March 2019 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, . [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/ RFC4862, September 2007, . [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, . [RFC7037] Yeh, L. and M. Boucadair, "RADIUS Option for the DHCPv6 Relay Agent", RFC 7037, DOI 10.17487/RFC7037, October 2013, . [RFC7217] Gont, F., "A Method for Generating Semantically Opaque Interface Identifiers with IPv6 Stateless Address Autoconfiguration (SLAAC)", RFC 7217, DOI 10.17487/ RFC7217, April 2014, . [RFC7653] Raghuvanshi, D., Kinnear, K., and D. Kukrety, "DHCPv6 Active Leasequery", RFC 7653, DOI 10.17487/RFC7653, October 2015, . [RFC7819] Jiang, S., Krishnan, S., and T. Mrugalski, "Privacy Considerations for DHCP", RFC 7819, DOI 10.17487/RFC7819, April 2016, . [RFC7824] Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy Considerations for DHCPv6", RFC 7824, DOI 10.17487/ RFC7824, May 2016, . [VitalQIP] Nokia, "Nokia VitalQIP", 2017, . [WIDE_DHCPv6] KAME project, "WIDE DHCPv6", 2008, . [draft-ren-dhc-mredhcpv6] Ren, G., He, L., and Y. Liu, "Multi-requirement Extensions for Dynamic Host Configuration Protocol for IPv6 Ren, et al. Expires September 11, 2019 [Page 10] Internet-Draft problem statement of mredhcpv6 March 2019 (DHCPv6)", March 2017. [kea_dhcp_hook_developers_guide] Internet Systems Consortium, "Hook Developer's Guide", 2018, . Authors' Addresses Gang Ren Tsinghua University Beijing, 100084 P.R.China Phone: +86-010 6260 3227 Email: rengang@cernet.edu.cn Lin He Tsinghua University Beijing, 100084 P.R.China Email: he-l14@mails.tsinghua.edu.cn Ying Liu Tsinghua University Beijing, 100084 P.R.China Email: liuying@cernet.edu.cn Ren, et al. Expires September 11, 2019 [Page 11]