Dynamic Host Configuration (DHC)                                  G. Ren
Internet-Draft                                                     L. He
Intended status: Informational                                    Y. Liu
Expires: July 15, August 7, 2020                              Tsinghua University
                                                        January 12,
                                                        February 4, 2020

               DHCPv6 Extension Survey and Considerations


   The manageability, security, privacy protection, and traceability of
   networks can be supported by extending the DHCPv6 protocol according
   to requirements.  This document provides a survey of current
   extension practices and typical DHCP server software on extensions,
   defines a DHCPv6 general model, discusses some extension points, and
   presents extension cases.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Current Extension Practices . . . . . . . . . . . . . . . . .   3
     3.1.  Standardized and Non-standardized DHCPv6 Extension Cases    3
     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  . . . . . . . . . . . . . .   4
   4.  Extension Points  . . Discussion  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  DHCPv6 General Model  . . . . . . . . . . . . . . . . . .   5
     4.2.  Extension Discussion Points  . . . . . . . . . . . . . . . . . . . .   5
       4.2.1.  Messages  . . . . . . . . . . . . . . . . . . . . . .   5
       4.2.2.  Options . . . . . . . . . . . . . . . . . . . . . . .   6
       4.2.3.  Message Processing Functions  . . . . . . . . . . . .   6
       4.2.4.  Address Generation Mechanisms . . . . . . . . . . . .   7
   5.  Extension Cases . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Normative  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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)
   [RFC8415] is an important a critical network protocol that can be used to
   dynamically provide IPv6 addresses and other network configuration
   parameters to IPv6 nodes.  Actually,  DHCPv6 continues to be extended and
   improved through new options, protocols or protocols, and message processing

   Although DHCPv6 provides more and more comprehensive functionalities
   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
   comprehensive insight into where and how to conduct extensions in
   DHCPv6 effectively.  The extensions to DHCPv6 can be various
   according to multiple and varied requirements.  The goal of multi-requirement multi-
   requirement extensions for DHCPv6 is to use simple interfaces to
   define and support more extensions without changing the basic design
   of DHCPv6.  Therefore, a detailed analysis is required to clarify the
   problems, design principles, and extract and unify the design
   specifications to help better solve the multi-requirement extension

   In summary, multi-requirement extensions for DHCPv6 can be conducted
   to support the administrator's self-defined functionalities.  As
   DHCPv6 is an important essential and useful protocol related to IPv6 addresses
   generation, it can provide more extended and flexible functionalities features 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 considerable amount of
   time will be taken to understand the open source 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 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 latest version of
   open-source server software comes out [kea_dhcp_hook_developers_guide] .
   [kea_dhcp_hook_developers_guide].  Hence, the multi-requirement
   extensions for DHCPv6 to solve administrators' specific problems are very necessary
   essential and significant.

   This document provides a survey of current extension practices and
   typical DHCP server software on extensions and gives DHCPv6 extension
   considerations by defining a DHCPv6 general model, discussing the
   extension problems, and presenting extension cases.

2.  Terminology

   Familiarity with DHCPv6 and its terminology, as defined in [RFC8415],
   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.  Newly-defined  New-defined options carry specific
                       parameters in 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 and provide better services, 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],
   [FreeRADIUS_DHCP], WIDE DHCPv6 [WIDE_DHCPv6], and DHCP Broadband
   [DHCP_Broadband].  Commercial and open source 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 provides extension APIs and 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 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.  Extension Points Discussion

   This section elaborates multi-requirement extensions for DHCPv6.
   Section 4.1 describes the general model of DHCPv6, while Section 4.2
   analyzes the extension points and requirements.

4.1.  DHCPv6 General Model

   Figure 1 summarizes the DHCPv6 general model and its possible
   extensions: messages, options, message processing functions, and
   address generation mechanisms.

+-----------------+                   +----------------+
|  DHCPv6 client  |    DHCP messages  |  DHCPv6 relay  |
| +-------------+ |    with options   | +------------+ | External inputs
| |  Message    | |<----------------->| |  Message   | |<----------------
| | processing  | |                   | | relaying   | | e.g., RADIUS
| | functions   | |                   | | functions  | | option [RFC7037]
| +-------------+ |                   | +------------+ |
+-----------------+                   +----------------+
                                DHCP messages |
                                with options  |
+-----------------+               +----------------------------+
|                 |   Extended    |        DHCPv6 server       |
|                 |   messages    | +-----------+ +----------+ |
|External entities|<------------->| |  Address  | | Message  | |
|                 |  e.g., Active | | generation| |processing| |
|                 |  leasequery   | | mechanisms| |functions | |
|                 |  [RFC7653]    | +-----------+ +----------+ |
+-----------------+               +----------------------------+

        Figure 1: DHCPv6 general model and its possible extensions.

4.2.  Extension Discussion Points

4.2.1.  Messages

   On the one hand, new messages can be designed and added to the DHCPv6
   protocol to enrich its funtionalities. functionalities.  For example, [RFC5007]
   defines new leasequery messages to allow a requestor to retrive retrieve
   information on the bindings for a client from one or more servers.
   [RFC7653] defines active leasequery messages to keep the requestor up
   to date with DHCPv6 bindings.

   On the other hand, people are concerned about the security and
   privacy issues of the 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.  Other nodes can see the options transmitted in
   DHCPv6 messages between DHCPv6 clients and servers.  Extended
   messages can be designed to secure the exchanges between DHCPv6 entities.

4.2.2.  Options

   DHCPv6 allows defining options to transmit parameters between DHCPv6
   entities for common requirements, e.g., DNS [RFC3646] and SNTP
   [RFC4075].  Also, these parameters may come from external entities.
   For example, [RFC7037] defines RADIUS option to exchange
   authorization and identification information between the DHCPv6 relay
   agent and DHCPv6 server.

   In other cases, network operators may require DHCPv6 messages to
   transmit some self-defined options between clients and servers.
   Currently, the vendor-specific information option allows clients and
   servers to exchange vendor-specific information.  Therefore,
   administrative domains can define and use the sub-options of vendor-
   specific the
   vendor-specific information option to serve their private purposes.
   The content of the self-defined options may come from two sources:
   devices and users.  If the content of self-defined options comes from
   users, 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 to the clients'
   requests.  But this always depends on other protocols to allow DHCPv6
   relays to get the information first.

4.2.3.  Message Processing Functions

   Although current commercial or open-source DHCP server software
   provides comprehensive functionalities, they still cannot meet all
   customers' requirements of processing DHCP requests.  Therefore, they
   will provide offer 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.  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 considers this extension.

4.2.4.  Address Generation Mechanisms

   Currently, the DHCPv6 servers assign addresses, prefixes and other
   configuration options according to their configured policies.
   Generally, different networks may prefer different address generation
   mechanisms.  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 utilized
   in DHCPv6 protocol as well.  The many types of IPv6 address
   generation mechanisms available have brought about flexibility and
   diversity.  Therefore, corresponding interfaces could be open and
   defined to allow other address generation mechanisms to be

5.  Extension Cases

   Administrative domains may enforce local policies according to their
   requirements, e.g., authentication, accountability.  Several kinds of
   multi-requirement extensions are presented in this section, including
   configurations in current DHCP software, option definition and server
   modification, and message definition between DHCPv6 entities and
   third-party entities.

   Currently, many DHCPv6 servers provide administrative mechanisms,
   e.g., host reservation and client classification.  Host reservation
   is often used to assign certain parameters (e.g., IP addresses) to
   specific devices.  Client classification is often used to
   differentiate between different types of clients and treat them
   accordingly in certain cases.

   To meet specific requirements, more

   More complicated extensions of DHCPv6 are needed. needed to meet specific
   requirements.  For example, considering such a requirement that DHCP
   servers assign IP addresses generated by user identifiers to the
   clients in a network to hold users accountable, 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 vendor-specific information option.
   The second one 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 in CPNR [CPNR] and hook
   mechanisms in Kea DHCP [Kea_DHCP] can be used.

   Some extensions for DHCPv6 may need the support of third-party
   entities.  For example, [RFC7037] introduces RADIUS entities into the
   message exchanges between DHCPv6 entities for better service
   provision.  In fact, the  The authentication in [RFC7037] can be also be used to meet
   the accountability requirement mentioned above because it is
   important to authenticate users first before assigning IP addresses
   generated from user identifiers.  Usually, this kind of extension
   requires the definition of messages communicated between DHCP
   entities and third-party entities, e.g., active leasequery [RFC7653].

   IPv6 addresses are related to manageability, security, traceability,
   and accountability of networks.  As DHCPv6 assigns IPv6 addresses to
   IPv6 nodes, it is important that DHCPv6 provides interfaces to allow
   administrative domains to conduct extensions to meet their multi-

6.  Security Considerations

   Security issues related with DHCPv6 are described in Section 22 of

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.  References

9.1.  Normative References

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,

   [RFC8415]  Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
              RFC 8415, DOI 10.17487/RFC8415, November 2018,

9.2.  Informative References

   [CPNR]     Cisco, "Cisco Prime Network Registrar", 2018,

              Weird Solutions, "DHCP Broadband", 2018,

              Ren, G., He, L., and Y. Liu, "Multi-requirement Extensions
              for Dynamic Host Configuration Protocol for IPv6
              (DHCPv6)", March 2017.

              FreeRADIUS, "FreeRADIUS DHCP", 2017,

   [GAGMS]    Liu, Y., He, L., and G. Ren, "GAGMS: A Requirement-Driven
              General Address Generation and Management System",
              November 2017.

              Internet System Consortium, "ISC DHCP", 2018,

              Internet System Consortium, "Kea DHCP", 2018,

              Internet Systems Consortium, "Hook Developer's Guide",
              2018, <https://jenkins.isc.org/job/Kea_doc/doxygen/df/d46/

              Microsoft, "IPv6 interface identifiers", 2013, <https://ww

              Microsoft, "Microsoft DHCP", 2008,

              Nominum, "Nominum DHCP", 2012,

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,

   [RFC3646]  Droms, R., Ed., "DNS Configuration options for Dynamic
              Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              DOI 10.17487/RFC3646, December 2003,

   [RFC4075]  Kalusivalingam, V., "Simple Network Time Protocol (SNTP)
              Configuration Option for DHCPv6", RFC 4075,
              DOI 10.17487/RFC4075, May 2005,

   [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,

   [RFC5007]  Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng,
              "DHCPv6 Leasequery", RFC 5007, DOI 10.17487/RFC5007,
              September 2007, <https://www.rfc-editor.org/info/rfc5007>.

   [RFC7037]  Yeh, L. and M. Boucadair, "RADIUS Option for the DHCPv6
              Relay Agent", RFC 7037, DOI 10.17487/RFC7037, October
              2013, <https://www.rfc-editor.org/info/rfc7037>.

   [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, <https://www.rfc-editor.org/info/rfc7653>.

   [RFC7819]  Jiang, S., Krishnan, S., and T. Mrugalski, "Privacy
              Considerations for DHCP", RFC 7819, DOI 10.17487/RFC7819,
              April 2016, <https://www.rfc-editor.org/info/rfc7819>.

   [RFC7824]  Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy
              Considerations for DHCPv6", RFC 7824,
              DOI 10.17487/RFC7824, May 2016,

   [RFC8415]  Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
              RFC 8415, DOI 10.17487/RFC8415, November 2018,

              Nokia, "Nokia VitalQIP", 2017,

              KAME project, "WIDE DHCPv6", 2008,

Authors' Addresses

   Gang Ren
   Tsinghua University
   Beijing  100084

   Phone: +86-010 6260 3227
   Email: rengang@cernet.edu.cn

   Lin He
   Tsinghua University
   Beijing  100084

   Email: he-l14@mails.tsinghua.edu.cn

   Ying Liu
   Tsinghua University
   Beijing  100084

   Email: liuying@cernet.edu.cn