Dynamic Host Configuration (DHC) G. Ren
Internet-Draft L. He
Intended status: Informational Y. Liu
Expires: August 7, 2020 Tsinghua University
February 4, 2020
DHCPv6 Extension Survey and Considerations
draft-ietf-dhc-problem-statement-of-mredhcpv6-03
Abstract
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.
Status of This Memo
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This Internet-Draft will expire on August 7, 2020.
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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 Discussion . . . . . . . . . . . . . . . . . . . . 5
4.1. DHCPv6 General Model . . . . . . . . . . . . . . . . . . 5
4.2. Extension 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. 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 a critical network protocol that can be used to
dynamically provide IPv6 addresses and other network configuration
parameters to IPv6 nodes. DHCPv6 continues to be extended and
improved through new options, protocols, and message processing
mechanisms.
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
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-
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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
problems.
In summary, multi-requirement extensions for DHCPv6 can be conducted
to support the administrator's self-defined functionalities. As
DHCPv6 is an essential and useful protocol related to IPv6 addresses
generation, it can provide more extended and flexible 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 considerable 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 latest 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
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. New-defined options carry specific
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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],
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 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 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
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runs as the network operator requires. Additionally, Kea DHCP allows
the network operator to use logging in the hooks library.
4. Extension 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 |
|
V
+-----------------+ +----------------------------+
| | 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 Points
4.2.1. Messages
On the one hand, new messages can be designed and added to the DHCPv6
protocol to enrich its functionalities. For example, [RFC5007]
defines new leasequery messages to allow a requestor to retrieve
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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 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 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 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 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 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 preferred address
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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
configured.
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.
More complicated extensions of DHCPv6 are 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 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
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message exchanges between DHCPv6 entities for better service
provision. The authentication in [RFC7037] can 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-
requirements.
6. Security Considerations
Security issues related with DHCPv6 are described in Section 22 of
[RFC8415].
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,
<https://www.rfc-editor.org/info/rfc4862>.
[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,
<https://www.rfc-editor.org/info/rfc8415>.
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9.2. Informative References
[CPNR] Cisco, "Cisco Prime Network Registrar", 2018,
<https://www.cisco.com/c/en/us/products/cloud-systems-
management/prime-network-registrar/index.html>.
[DHCP_Broadband]
Weird Solutions, "DHCP Broadband", 2018,
<https://www.weird-solutions.com/carrier-solutions/dhcp-
broadband>.
[draft-ren-dhc-mredhcpv6]
Ren, G., He, L., and Y. Liu, "Multi-requirement Extensions
for Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", March 2017.
[FreeRADIUS_DHCP]
FreeRADIUS, "FreeRADIUS DHCP", 2017,
<https://wiki.freeradius.org/features/DHCP>.
[GAGMS] Liu, Y., He, L., and G. Ren, "GAGMS: A Requirement-Driven
General Address Generation and Management System",
November 2017.
[ISC_DHCP]
Internet System Consortium, "ISC DHCP", 2018,
<http://www.isc.org/downloads/dhcp/>.
[Kea_DHCP]
Internet System Consortium, "Kea DHCP", 2018,
<https://www.isc.org/kea/>.
[kea_dhcp_hook_developers_guide]
Internet Systems Consortium, "Hook Developer's Guide",
2018, <https://jenkins.isc.org/job/Kea_doc/doxygen/df/d46/
hooksdgDevelopersGuide.html>.
[Microsoft]
Microsoft, "IPv6 interface identifiers", 2013, <https://ww
w.microsoft.com/resources/documentation/windows/xp/all/
proddocs/en-us/sag_ip_v6_imp_addr7.mspx?mfr=true>.
[Microsoft_DHCP]
Microsoft, "Microsoft DHCP", 2008,
<https://technet.microsoft.com/en-us/library/
cc896553(v=ws.10).aspx>.
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[Nominum_DHCP]
Nominum, "Nominum DHCP", 2012,
<https://www.nominum.com/press_item/nominum-releases-new-
version-of-carrier-grade-dhcp-software-for-telecom-
providers/>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<https://www.rfc-editor.org/info/rfc2464>.
[RFC3646] Droms, R., Ed., "DNS Configuration options for Dynamic
Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
DOI 10.17487/RFC3646, December 2003,
<https://www.rfc-editor.org/info/rfc3646>.
[RFC4075] Kalusivalingam, V., "Simple Network Time Protocol (SNTP)
Configuration Option for DHCPv6", RFC 4075,
DOI 10.17487/RFC4075, May 2005,
<https://www.rfc-editor.org/info/rfc4075>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.
[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,
<https://www.rfc-editor.org/info/rfc7217>.
[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>.
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[RFC7824] Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy
Considerations for DHCPv6", RFC 7824,
DOI 10.17487/RFC7824, May 2016,
<https://www.rfc-editor.org/info/rfc7824>.
[VitalQIP]
Nokia, "Nokia VitalQIP", 2017,
<https://networks.nokia.com/products/vitalqip-ip-address-
management>.
[WIDE_DHCPv6]
KAME project, "WIDE DHCPv6", 2008,
<http://ipv6int.net/software/wide_dhcpv6.html>.
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
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